Family: Toxocaridae. Genus: Toxocara. Toxocara cams (Werner, 1782) Johnston, 1916. Toxocara cati (Schrank, 1788) Brumpt, 1927. Family: Anisakidae.
Authors
Katarzyna Bartosik, Chair and Department o f Biology and Parasitology, Medical University o f Lublin Alicja Buczek, Chair and Department o f Biology and Parasitology, Medical University o f Lublin D anuta Cielecka, Department o f General Biology and Parasitology, Medical University o f Warsaw Agnieszka Cisowska, Department o f General Biology and Medical Parasitology, Medical University o f Wroclaw Barbara Grytner-Zięcina, Department o f General Biology and Parasitology, Medical University o f Warsaw Bożena Kiziewicz, Department o f General Biology, Medical University o f Białystok Przemysław Kosieliński, Department o f General Biology, Medical University o f Białystok W anda Kuźna-Grygiel, Chair and Division o f Biology and Medical Parasitology, Pomeranian Medical University, Szczecin Przemysław M yjak, Department o f Tropical Parasitology, Institute o f Maritime and Tropical Medicine, Medical University o f Gdańsk, Gdynia Tomasz Olszewski, Chair and Department o f Biology and Parasitology, Medical University o f Lublin Krzysztof Olszewski, Chair and Department o f Biology and Parasitology, Medical University o f Lublin Wojciech Piasecki, Division of Fish Diseases, Agricultural University o f Szczecin Zb igniew Pokora, Department o f General and Molecular Biology and Genetics, Medical University o f Silesia, Katowice Krzysztof Solarz, Department o f Parasitology, Medical University o f Silesia, Sosnowiec Joanna Stańczak, Departm ent o f Tropical Parasitology, Institute o f Maritime and Tropical Medicine, Medical University o f Gdańsk, Gdynia M onika Turkowicz, Department o f General Biology and Parasitology, Medical University o f Warsaw Dorota Wojnicz, Department o f General Biology and Medical Parasitology, Medical University o f Wroclaw
PARASITOLOGY FOR MEDICAL STUDENTS
E d ite d by A lic ja B uczek
$
k o lib e r
LUBLIN 2oo6
COVER DESIGN: S e b a s t i a n b u c z e k buuucz 3 hotmail. com ENGLISH PROOF - READING: MAREK SĘKOWSKI Published by Fundacja na Rzecz Zwalczania Kleszczy i Profilaktyki w Chorobach Odkleszczowych w Lublinie
Copyright © 2006 Fundacja na Rzecz Zwalczania Kleszczy i Profilaktyki w Chorobach Odkleszczowych
All rights reserved. No part o f this w o rk m ay be reproduced w ith o u t th e prior w ritte n permission o f th e publisher.
ISBN 83-60497-30-3 Printed in Poland at KOLIBER, Lublin
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p a r a s it e diseases constitute one o f the most serious health problems in the whole world. They are connected w ith wide distribution o f parasites in different regions, various ways o f their transmission to hosts, avoiding by parasites host immune response, parasites adaptations to th e ir m icrohabitats, and still little knowledge about laboratory and clinical diagnosis o f parasitic diseases. Therefore, more than ever, there is the necessity o f greater understanding o f the interactions between parasites and the ir hosts, pathogenesis and clini cal manifestations o f parasite diseases, influence o f human behavior on the distribution o f parasites as w ell as morphology and biology o f parasites. his book is meant to be a practical handbook for students o f medical university, pre medical students, and students in international health and other branches o f public health. It includes crucial inform ation used in medical parasitology and a number o f exercises for better understanding o f parasitological problems. During our course o f parasitology, special emphasis is placed on the geographic distribution o f human parasites, morphology and life cycle o f parasites, clinical features and pathogenesis o f parasitic diseases and the most reliable technique fo r diagnosing parasites. he authors hope th a t the content o f this text w ill stim ulate all students to learn prac tical parasitology and to read supplementary books. We welcome any suggestions or com ments fo r a possible im provem ent o f the next edition o f the parasitology book.
Lublin, July 2006
Contents
1.
PARASITISM
9
1.1.
Parasites and their environment • Alicja Buczek, Tomasz Olszewski
9
1.1.1. The term parasitism
9
1.1.2.
Parasites - definitions and criteria o f classification
1.1.3.
Hosts - definitions and criteria o f classification
12
1.1.4.
The m acrohabitat and m icrohabitat o f parasites
13
1.1.5.
Sources o f parasite infestation
18
1.1.6.
Routes o f parasite invasion
1.1.7. Transmission o f parasites
9
22 25
1.2.
Parasites and hosts interactions • Alicja Buczek,Krzysztof Olszewski
29
1.2.1.
Parasitosis
29
1.2.1.1.
Signs and symptoms o f human parasitoses
31
1.2.2.
Mechanisms o f host injury by parasites
34
1.2.2.1. Physical injury
34
1.2.2.2. Loss o f nourishm ent
34
1.2.2.3.
Toxic activity
35
12.2.4.
Transmission and maintenance o f pathogens
35
12.3.
Immunological response in parasitic infections
36
13.
D istribution and epidemiology o f parasitoses
39
13.1.
World distribution o f parasitoses
39
13.2.
Factors influencing parasitosis distribution
39
2. PROTOZOA
43
2.1 3rotozoa o f medical importance • Przemysław Myjak, Zbigniew Pokora
43
3. THE PLATYHELMINTHES
123
3.L
The Trematodes • Agnieszka Cisowska, Dorota Wojnicz
123
3.LL
Intestinal flukes
126
3 12 .
The liver flukes
11.3
The blood flukes
140
132
3 14
The lung flukes
144
32
~ne Cestodes • Barbara Grytner-Zięcina, Danuta Cielecka,Monika Turkowicz
152
4. THE NEMATODES
183
4.1. Intestinal nematodes • Zbigniew Pokora, Wojciech Piasecki, Wanda Kuźna-Grygiel
186
4.2. The tissue nematodes 4.3. The filarial nematodes •
203
Bożena Kiziewicz, Przemysław Kosieliński
5. THE ARTHROPODS
213
225
5.1.
Insects o f medical importance • Joanna Stańczak
225
5.2.
Mites (Acari) o f medical importance • Krzysztof Solarz
257
5.3. Ticks o f medical importance • Alicja Buczek
6. DIAGNOSTICS OF PARASITIC DISEASES Stool analysis • Alicja Buczek, Katarzyna Bartosik
289
309
6.1.
309
6.1.1. General principles o f stool analysis
309
6.1.2. Procedure o f collecting a stool specimen and the prelim inary observations
310
6.1.3. Preservatives
313
6.1.4. Methods o f specimen staining
313
6.1.5. Examining fresh stool specimens
314
6.1.6. Concentration methods
315
6.2.
Blood analysis
317
6.3.
Analysing body fluids and tissues
318
6.3.1. Analysing saliva, secretions o f the respiratory tract and lung tissue
318
6.3.2. Urine analysis
320
6.3.3. Fluids obtained from punctures and tissue biopsy
320
6.3.4. Analysis o f duodenal contents
322
6.4.
Culture methods
323
6.5
Immunological methods
324
6.6.
Polymerase chain reaction
325
4. THE NEMATODES
183
4.1. Intestinal nematodes • Zbigniew Pokora, Wojciech Piasecki, Wanda Kuźna-Grygiel
186
4.2. The tissue nematodes 4.3. The filarial nematodes •
203
Bożena Kiziewicz, Przemysław Kosieliński
5. THE ARTHROPODS
213
225
5.1.
Insects o f medical importance • Joanna Stańczak
225
5.2.
Mites (Acari) o f medical importance • Krzysztof Solarz
257
5.3.
Ticks o f medical importance • Alicja Buczek
289
6. DIAGNOSTICS OF PARASITIC DISEASES Stool analysis • Alicja Buczek, Katarzyna Bartosik
309
6.1.
309
6.1.1. General principles o f stool analysis
309
6.1.2. Procedure o f collecting a stool specimen and the prelim inary observations
310
6.1.3. Preservatives
313
6.1.4. Methods o f specimen staining
313
6.1.5. Examining fresh stool specimens
314
6.1.6. Concentration methods
315
6.2.
Blood analysis
317
6.3.
Analysing body fluids and tissues
318
6.3.1. Analysing saliva, secretions o f the respiratory tract and lung tissue
318
6.3.2. Urine analysis
320
6.3.3. Fluids obtained from punctures and tissue biopsy
320
6.3.4. Analysis o f duodenal contents
322
6.4.
Culture methods
323
6.5
Immunological methods
324
6.6.
Polymerase chain reaction
325
4. THE NEMATODES
The n e m a to d e s are u nse g m e n te d w o rm s, u su a lly c y lin d ric a l and e lo n g a te in shape. They are e co lo g ica lly d iv e rs ifie d , because o n ly a sm a ll fra c tio n o f th e species are p arasite s o f anim als. The m a jo rity o f n e m a to d e s are fre e -liv in g . The b o d y w a ll o f n e m a to d e s co nsists o f th re e m a jo r layers: cu ticle , h y p o d e rm is and m u scu la tu re . The c u ticle is a n o n -n u cle a te d la m in a r s tru c tu re secreted by th e u n d e rly in g h yp o d e rm is. It is u su a lly s m o o th b u t m ay be s tria te d , bossed, or o rn a m e n te d w ith spines. The b asically th re e -la y e r c u ticle is n o t an in e rt se cre tio n b u t a m e ta b o lic a lly a ctive s tru c tu re . U sually a ro u n d th e m o u th , and a t tim e s in th e cervical, anal, and ca udal regions, th e re are sessile or p e d u n c u la te d p ap illa e , w h ich are p ro b a b ly sensory in fu n c tio n . U nder th e c u ticle is th e h y p o d e rm is, w h ich , in m a tu re n em ato de s, appears as a s y n c y tiu m o f in te rm in g le d n uclei and fib re s . B elow is th e layer o f lo n g itu d in a l s o m a tic m uscles (no a n ta g o n is tic circ u la r m uscle layer is p re se n t in n em ato de s). A risin g fro m th e h y p o d e rm is and p ro je c tin g in to th e bod y c a v ity are fo u r lo n g itu d in a l cords, s itu a te d dorsally, v e n tra lly , and la te ra lly. The la te ra l cords co n ta in th e lo n g itu d in a l canals o f e x c re to ry system . The d o rsa l and v e n tra l cords co n ta in th e nerve tru n k s . The b o d y ca vity, fille d w ith p se u d o co e lo m ic flu id , c o n ta in s th e d ig e stive system , th e e x cre to ry system , and th e re p ro d u c tiv e system . N e m a tod e s have a co m p le te , fu n c tio n a l d ig e stive system (g u t tra c t). It consists o f th e o ra l ca vity, oesophagus, m id g u t and th e h in d g u t w ith anus. The fo o d o f p a ra s itic n em ato de s co nsists o f h o st tissues, h o t blood o r m ucus and h ost in te s tin a l c o n te n ts. N e m a tod e s do n o t have c irc u la to ry system , b u t b o d y flu id s th a t co n ta in h a e m o g lo b in b a th e th e va rio u s organs. The re q u ire m e n t fo r oxygen va ries g re a tly a m o n g w o rm s, b u t even th o se u su a lly conside re d to be c o m p le te ly a n a e ro b ic m ay re q u ire m in u te a m o u n ts o f fre e oxygen. N e m a tod e s are d io e cio u s a n im a ls (the sexes are se pa ra te). P arasitic fo rm s d e m o n s tra te sexual d im o rp h is m , w ith th e fe m a le s b e in g m uch la rg er th a n th e m ales. O th e r e x te rn a l d iffe re n ce s b e tw e e n th e sexes in clu d e th e s tru c tu re o f th e p o s te rio r p a rt o f th e b o d y and th e lo ca tio n o f g e n ita l pores. The m ale o rgans are com posed o f a sin g le te s tis and e ja c u la to ry d u ct w h ic h opens in to th e cloaca. The fe m a le organs are com posed o f tw o u te ri* tw o ovaries, tw o o vid u cts, and one va gina . Som e fre e -liv in g and also som e p a ra s itic fo rm s have o n ly one u te ru s and ovary. On th e o th e r hand, th e u te ri m ay be
183
su b d iv id e d , so th a t fo rm s w ith up to 16 u te ri are kn o w n . The vu lva m ay be fo u n d in v a rio u s p o sitio n s, even q u ite close to th e a n te rio r e x tre m ity (as in p in w o rm , E n te ro b iu s , sp.) and th e u te ri m ay run in o p p o s ite d ire c tio n s (a m p h id e lp h ic ) or b o th run backw ards (o p is th o d e lp h ic ). The o va ry is p ro x im a lly a solid, cy lin d ric a l org an c o n ta in in g a n u m b e r o f cells, w h ich d iv id e to fo rm th e ova. They pass th ro u g h an o v id u c t to th e s e m in a lje c e p ta c le , a sm a ll d ila te d p a rt o f th e org an in w h ic h s p e rm a to zo a are stored and fe rtiliz a tio n ta ke s place. This is fo llo w e d by th e u te ru s, in w h ic h th e egg-shells are fo rm e d a n d /o r th e e m b ryo m ay develop. The u te ri are u su a lly conn e cte d to th e va gina by m u scu lar o veje cto rs. The v u lva is u su a lly s itu a te d on th e v e n tra l surface. Some n e m a to d e s are o vip a ro u s, o th e rs are v iv ip a ro u s (o vo vivip a ro u s). The eggs va ry g re a tly in shape and size, a fa c t w h ic h is o f g re a t im p o rta n c e in m a k in g a sp ecific d ia gn o sis by faeces e x a m in a tio n . The o rig in a l egg cell d ivid e s in to tw o , th e n fo u r and so on, and th e e m b ryo passes th ro u g h a m o ru la stage and la te r th ro u g h a ‘ta d p o le ’ stage, in w h ich th e a n te rio r end is broad and th e e m b ryo is b e n t d o u b le . E ve n tu a lly th e larva is fu lly fo rm e d and ready to hatch. N o rm a lly fo u r m o u lts (ecdyses), in w h ich th e w h o le c u tic le is shed and replaced by a new one, ta ke place b efo re th e a d u lt stage is reached, b u t in som e cases a m o u lt m ay be o m itte d . The s e q u e n tia l larval stages are: firs t-s ta g e larva (LI), se cond-stage larva (L2), th ird -s ta g e larva (L3), and fo u rth -s ta g e larva (L4). The larval w o rm becom es in fe c tiv e fo r th e fin a l h o st as a ru le a fte r th e second m o u lt (as L3). The in fe c tiv e stage m ay, in ce rta in species, be reached in th e egg-shell. In species w h ich use an in te rm e d ia te host, th e in fe c tiv e larva develops in sid e th is host. In fe c tio n o f th e h ost in w h ic h th e a d u lt n e m a to d e s occur m ay be e ffe cte d by: 1) an a ctive, n o n -p a ra s itic th ird larva w h ic h e nte rs th e h o st th ro u g h its skin (S tr o n g y lo id e s ), 2) a passive in fe c tiv e egg c o n ta in in g a second o r th ird in fe c tiv e larva (A s c a ris ), 3) an in te rm e d ia te h o st in w h ic h th e in fe c tiv e larva develops. In the se in stan ce s th e in te rm e d ia te h o st is e ith e r eaten by th e d e fin itiv e h o st (M e ta s tr o n g y lu s ) or it conveys th e in fe c tiv e larva to th e d e fin itiv e h ost and th e in fe c tiv e larva th e n p e n e tra te s th ro u g h th e skin o f th e d e fin itiv e h o st (F ilarioidea). The th ird and fo u rth ecdyses ta ke place in th e fin a l host, a fte r w h ic h th e w o rm s are in th e a d u lt stage and g ro w to m a tu rity . R e spiration o f a d u lt n e m a to d e s m ay be basically s im ila r to th a t o f a d u lt cestodes, b u t w ith g re a te r use o f th e n o rm a l c itric acid cycle.
Classification of the most important species of nematodes of medical importance PHYLUM: NEMATODA CLASS: SECERNENTEA O rder: A scarid ida Fam ily: A scarid ida e
184
G enus: A s c a ris
Ascaris lumbricoides Linnaeus, 1758 Fam ily: O xyurid ae G enus: E n te ro b iu s
Enterobius vermicularis (Linnaeus, 1758) Leach, 1853 Fam ily: T o xocaridae Genus: Toxocara
Toxocara cams (Werner, 1782) Johnston, 1916 Toxocara cati (Schrank, 1788) Brumpt, 1927 Fam ily: A nisa kid a e G enus: A n is a k ls
Anisakis simplex Rudolphi, 1809 O rder: R h a b d itid a Fam ily: S tro n g y lo id id a e G enus: S tr o n g y lo id e s
Strongyloides stercoralis (Bavay, 1876) Stiles et Hassal, 1902 O rder: S tro n g ylid a Fam ily: A n c y lo s to m id a e G enus: A n c y lo s to m a
Ancylostoma duodenale (Dubini, 1843) Creplin, 1845 Fam ily: U n cin a riid a e Genus: N e c a to r
Necator americanus (Stiles, 1903) Stiles, 1906 O rder: C a m a lla n ida Fam ily: D ra cu ncu lida e Genus: D ra c u n c u lu s
Dracunculus medinensis (Linnaeus, 1758) Gatlandant, 1773 CLASS: ADENOPHOREA O rder: T rich o ce p h a lid a Fam ily: T ric h in e llid a e Genus: T ric h in e lla
Trichinella spiralis (Owen, 1835) Raillet, 1895 Fam ily: C a p illa riid a e
Capillaria philippinensis Chitwood, Valesquez et Salazar, 1968 Fam ily: T rich u rid a e
Trichuris trichiura (Linnaeus, 1771) Stiles, 1901
185
4.1. Intestinal nematodes
Ascaris lumbricoides Linnaeus, 1758 g ia n t h u m a n r o u n d w o r m
Geographic Distribution. C o s m o p o lita n , b u t th e p a ra s ite is m o s t p r e v a le " in w a rm , m o is t re g io n s o f th e w o rld .
Morphology. F e m a le s a re d is tin c tly la rg e r th a n m a le s, m e a s u rin g . 2 0 -3 5 cm b y 3 - 6 m m , a n d h a v in g a s tr a ig h t ta il. T h e v u lv a is s itu a te d m id - v e n tr a lly n e r th e ju n c tio n o f th e a n te r io r - a n d m id d le th ir d s o f th e b o d y . T h e v u lv a e x te n d s a s in g le
v a g in a , th e
la tte r b ra n c h in g
in to
tw o
~ :c
s e ts o f g e n ita l tu b u le s , eac~
c o n s is tin g o f u te ru s , s e m in a l re c e p ta c le , o v id u c t, a n d o v a ry . T h ese tu b u le s a '= c o ile d th r o u g h th e m id d le a n d p o s te rio r th ir d s o f th e b o d y . M a le s a re 15-31 c r lo n g by 2 - 4 m m , a n d t h e ir ta il is c u rv e d v e n tra lly . T h e ir g e n ita lia c o n s is t o f a io - g s in g le tu b u le m a d e u p o f te s tis , vas d e fe re n s , a n d e ja c u la to ry d u c t, w h ic h
s
to r tu o u s ly c o ile d in th e p o s te rio r h a lf o f th e w o rm and o p e n s in to th e cloaca w h ic h is s u b te rm in a l. A p a ir o f e q u a l a nd s u b e q u a l c o p u la to ry s p ic u le s is s itu a te :: in a p o c k e t d o rs a l to th e g e n ita l tu b u le . T h e re is n o g u b e rn a c u lu m . F e rtile eggs are b ile -s ta in e d , w ith a th ic k , tra n s p a re n t s h e ll, c o n s is tin g o f a re la tiv e ly n o n -p e rm e a b le
in n e rm o s t lip o id a l v ite llin e
fo u n d in u n fe rtiliz e d eggs), a th ic k c h itin o u s m id d le
m e m b ra n e
(w h ic h
is n o :
la ye r, a n d an o u te rm o s t
c o a rs e ly m a m m illa te d a lb u m in o id la ye r. T h ey m e a s u re 5 5 -7 5 p m by 3 5 -5 0 p m . I's o m e in s ta n c e s , th e o u te r, m a m m illa te d la y e r is a b s e n t. Such eggs are re fe rre d to as d e c o rtic a te d . The o v u m c o n ta in s a m ass o f co arse le c ith in g ra n u le s w h e n th e e gg is d is c h a rg e d in th e fae ce s. In fe rtile eggs are d is tin c tly m o re e lo n g a te , 8 5 -9 5 p m by 4 3 -4 7 p m , have th in sh ells, w ith th e m a m m illa te d e x te rn a l la ye r v a ry in g fro m
g ro ssly
irre g u la r
m a m m illa tio n s
to
a
re la tiv e ly
s m o o th
la ye r
a lm o s t
c o m p le te ly la c k in g m a m m illa tio n s . Such eggs, p ro d u c e d by u n m a te d fe m a le s , are fre q u e n tly seen in th e faeces.
Biology and life cycles. A d u lt w o rm s u s u a lly live in th e sm a ll in te s tin e lu m e n , fe e d in g on p re -d ig e s te d h o s t fo o d , chym e , o r h o s t c e llu la r d e b ris. They do n o t have a tta c h m e n t o rg an s and th e re fo re th e y a ssum e s-sh a pe c o n fig u ra tio n , p e rp e tu a lly m o v in g “ u p s tre a m " a g a in s t th e p e rista lsis. A fte r m a tin g , th e fe m a le b e g in s to p ro d u ce fe rtiliz e d u n e m b ry o n a te d eggs w h ic h pass o u t fro m th e h o s t w ith faeces. An average fe m a le p ro du ce s som e 200 0 0 0 eggs per day. G e n ita l tu b u le s o f a sin g le fe m a le m ay c o n ta in up to 27 m illio n eggs! In th e e x te rn a l e n v iro n m e n t, th e eggs re q u ire a p e rio d o f in c u b a tio n (2 -4 w eeks) b e fo re th e y are in fe c tiv e . In th e d e v e lo p m e n t o f A s c a ris lu m b r ic o id e s , as in o th e r n e m a to d e s,
186
th e re are fo u r larval stages fo llo w e d by a d u lt, w ith a m o u lt b e tw e e n th e successive stages. Tw o firs t m o u lts o ccu r in th e egg, so th e in fe c tiv e stage is a L3 la rva 41. W hen in fe c tiv e eggs are s w a llo w e d , th e se larvae h atch in th e sto m a ch and th e u p p e r s m a ll in te s tin e . They a ctive ly m ig ra te in to th e in te s tin a l w a ll, th e n th ro u g h th e p o rta l c irc u la tio n to th e liver, th e rig h t heart, and in to th e p u lm o n a ry vessels, th e n to th e in te ra lv e o la r tissu e s o f th e lungs. A fte r g ro w th and e sse n tia l d e v e lo p m e n t in th e lungs, th e larvae m ig ra te o r are carried in th e m ucus flo w th ro u g h th e re s p ira to ry passages to th e th r o a t w h e re th e y are sw a llo w e d . In th e s m a ll in te s tin e th e y g ro w , m o u lt tw ice , and m a tu re .
Disease. A scariasis (a s c a rio s is ). Pathogenesis. The p a th o g e n ic e ffe cts o f ascariosis are due to th e fo llo w in g m e ch an ism s: im m u n e re a ction s o f th e h ost, m e ch an ica l e ffe c ts o f th e a d u lt w o rm s , and th e e ffe cts o f a d u lt w o rm s on th e h o s t’s n u tritio n . Pathology. A t th e stage o f la rva l m ig ra tio n , th e fir s t passage o f larvae th ro u g h th e live r and lungs pro voke s no re m a rka b le p a th o lo g ic changes or s y m p to m s unless th e n u m b e r o f larvae is im m ense. H ow ever, s u b se q u e n t m ig ra tio n s due to re -in fe c tio n m ay cause in te n s e tis s u e re a ctio n in b o th live r and lungs even w h e n n u m b e r o f larvae in vo lve d is re la tiv e ly sm all. In lungs th is p a th o lo g ic process is kn o w n as A s c a ris p n e u m o n itis 42, being th e re s u lt o f th e p a th o lo g ic process co up le d w ith an a lle rg ic re a ction . In te s tin a l a scariosis is associated w ith s ig n ific a n t n u tritio n a l im p a irm e n t, w h ic h is m ore o r less p ro p o rtio n a l to th e w o rm burde n . A d u lt w o rm s do n o t a tta c h to th e in te s tin a l w a ll b u t m a in ta in th e ir p o s itio n by c o n s ta n t m o ve m e n t. They o cca sio n a lly fo rce th e ir w a y in to e x tra in te s tin a l sites, o r if p re se n t in large n u m b e rs fo rm ta n g le d masses th a t o cclude th e bow el. Those th a t m ig ra te u p w a rd m ay e n te r and b lo ck th e b ilia ry or p a n cre a tic d uct, re s u ltin g in acute b ilia ry o b s tru c tio n o r acute p a n c re a titis 43. P e n e tra tin g in to h e p a tic o r caval ve no u s channels, w o rm s m a y be carried as e m b o li to th e b rain, heart, and lungs. M ig ra tin g fu r th e r up th e a lim e n ta ry tra c t th e w o rm s gain access to several o th e r a p e rtu re s . M o s t co m m o n ly th e y are s im p ly e xpelled or cra w l fro m th e m o u th . They m ay e n te r th e nasal m e a tu s via th e n a so p h a ryn x and e x it th ro u g h a naris. Rarely, a la c rim a l d u c t m ay be e nte re d by an im m a tu re w o rm , and th e w o rm a tte m p ts to e x it in to th e eye. L ikew ise a w o rm in th e o ro p h a ry n x m ay e n te r th e E ustachian tu b e and p e n e tra te to th e m id d le ear and th ro u g h th e ty m p a n ic m e m b ra n e to th e e x te rn a l a u d ito ry m eatus. W o rm s m ig ra tin g d o w n w a rd becom e lodged in th e a p p e n d ix and m ay cause o b s tru c tiv e a p p e n d ic itis . They m ay 41 Formerly, it was considered, that the first moult occurred in the egg, two next moults - in the lungs, and the last one took place in the small intestine. 42 Inflammation of the lungs. 43 Inflammation of the pancreas.
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p e rfo ra te th e in te s tin a l w a ll w e a ken e d by g angrene fro m p ro lo n g e d ileus, or perhaps even th e in ta c t w a ll. W o rm s m ay reach o th e r site s such as th e kid n e y via fis tu la fo rm e d a fte r in te s tin a l p e rfo ra tio n . In th e m a jo rity o f ascariosis cases, h ow eve r, th e e x tra in te s tin a l p a th o lo g y is rare.
Symptoms. The in g e s tio n o f sm a ll n u m b e rs o f in fe c tiv e eggs p ro b a b ly gives rise to no recognisable sym p to m s, b u t la rg er n um be rs m ay p rovoke p n e u m o n itis d u rin g la rva l m ig ra tio n th ro u g h th e lungs. The s y m p to m s co nsist o f d ysp n e a 44, o fte n o f th e a s th m a tic typ e , a dry or p ro d u c tiv e cough, rales th a t are u s u a lly w h e e z in g or coarse b u t ra re ly c re p ita n t, m o d e ra te feve r, tra n s ie n t e o s in o p h ilia 45, and X -ray fin d in g s o f sca tte re d , s h iftin g , m o ttle d lu n g in filtra tio n su g g e stive o f v ira l p n e u m o n ia . This p ic tu re o f tra n s ie n t p u lm o n a ry in filtra tio n , a ssociated w ith m a rked p e rip h e ra l e o s in o p h ilia , is called L o ffle r’s syn drom e. In te s tin a l ascariosis te n d s to be w e ll to le ra te d unless th e in fe c tio n is heavy o r in ta k e o f n u trie n ts by th e h ost is in a d e q u a te . In u sual in fe c tio n in ch ild re n , th e re m ay be in te r m itte n t co licky cram ps, loss o f a p p e tite , and fre tfu ln e s s . The a b d o m e n is o fte n p ro tu b e ra n t. The lo n g -te rm e ffe c t o f th e m a ln u tritio n caused by ascariosis m ay be g ro w th im p a irm e n t.
Epidemiology. It is e stim a te d th a t som e 1.3 b illio n peo p le w o rld w id e are in fe c te d w ith A s c a ris lu m b r ic o id e s , (w ith 530 m illio n in China alone). H um an in fe c tio n w ith A s c a ris lu m b r ic o id e s is a cqu ire d by s w a llo w in g fu lly e m b ryo n a te d eggs. An im p o rta n t fa c to r fo r th e e p id e m io lo g y o f A s c a ris has been th e e xtre m e re sista nce o f A s c a ris eggs to adverse e n v iro n m e n ta l c o n d itio n s . They can su rvive deep fre e z in g and d ire c t a ctio n o f ce rta in chem icals. In m o is t so il th e y can re ta in v ia b ility up to 6 years. They are se n sitive to d esicca tio n o r d ire c t a ctio n o f sun lig h t. There are m any ro u te s o f th e p arasite tra n s m is s io n . The in fe c tiv e eggs may be p re se n t in c o n ta m in a te d soil, ve g e ta b le s o r fru its fro m fie ld s or gardens fe rtiliz e d w ith h u m a n e xcre m e nts etc. Finally, w e can in fe c t ourselve s s im p ly fro m d irty hands. In e n d e m ic areas even a p p a re n tly clean hands m ay carry th e in fe c tiv e eggs a fte r sh a kin g hands, to u c h in g b a n kn o te s o r even d o o r knobs. In c e rta in lo ca litie s it is possible th a t a irb o rn e eggs o f th is n e m a to d e m ay be in h ale d w ith d u s t p a rticle s and th u s s ta rt th e in fe c tio n . An im p o rta n t fa c to r in m a in ta in in g e n d e m ic ity o f ascariosis m ay be co p ro p h a g y o f v a rio u s a nim als. D ung beetles, w h ile “ b u ttin g ” and in g e s tin g fa e ca l m a tte r, s c a tte r and m ix th e faeces w ith soil, w h ic h p ro m o te s tra n s m is s io n . Y oung dogs a vid ly eat fresh h u m a n stools, as do ce rtain v u ltu re s . The d o m e s tic pig like w ise eats h um an stoo ls, e specially if g arnish e d w ith m a ggots. As A s c a ris eggs pass unchanged th ro u g h th e in te s tin e o f th e se anim als, th e re su lt is th a t eggs in stoo ls placed a t so cia lly accep tab le lo ca tio n are tra n s p o rte d and d e p o site d a t lo ca tio n s m ore
44 Laboured breathing. 45 The formation and accumulation of an abnormally large number of eosinophils in the blood.
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a d v a n ta g e o u s to th e p arasite . There have been a t least tw o re p o rte d cases o f tra n s p la c e n ta l tra n s m is s io n o f A s c a ris fro m a m o th e r to a fo e tu s . This p h e n o m e n o n is q u ite co m m o n in a n im a l ascarid in fe c tio n s , b u t ve ry little is kn o w n a b o u t it ’s e xte n d in h um ans. The issue o f p ossible tra n s m is s io n o f A . lu m b r ic o id e s to - and fro m o th e r m a m m a ls has re m a in e d c o n tro v e rs ia l. It is also u ncle a r w h e th e r th e re la ted p arasite, A s c a ris s u u m , (specific to pigs) can be in fe c tiv e to hum ans.
Diagnosis. This is m ade by d e m o n s tra tio n o f th e n e m a to d e eggs in faeces (Fot. 6.2). The fa irly c o n s ta n t n u m b e r p ro du ce d by each fe m a le p e rm its (experienced la b o ra to ry p ersonnel) a te n ta tiv e e s tim a tio n o f th e p arasite n u m b e rs ju d g in g fro m th e egg d e n s ity in th e fae ca l sam ple. In te s tin a l ascariosis m ay be also d ia gn o sed as a re s u lt o f ra d io g ra p h ic s tu d y o f th e g a s tro in te s tin a l tra c t. In th e e arly stages o f in fe c tio n , if su spicion o f ascariosis is stro ng , based on clin ic a l evidence o f A s c a ris p n e u m o n itis , a d ia g n o sis m ay be m ade by fin d in g larvae in th e s p u tu m o r in g a stric w a sh ing s.
Enterobius vermicularis (Linnaeus, 1758) Leach, 1853 p in w o rm
Geographic Distribution. C o sm o p o lita n (m o st p re va le n t in th e te m p e ra te c lim a tic zone).
Morphology. M ales are 2 -5
m m lo n g by 0.2 m m w id e , w ith curved p o s te rio r ends, fe m a le s are 8-13 m m long by 0 .3 -0 .5 m m w id e , and have long p o in te d ta ils . The v u lva opens m id -v e n tra lly , p ro x im a te ly in m id -le n g th o f th e body. In b o th sexes, th e re are ce ph a lic w in g -lik e p ro je c tio n s (alae), and th e oeso p ha g us is d ivid e d in to th re e p o rtio n s : a corpus, isth m u s, and bulb. M id p o rtio n o f th e fe m a le bod y is s u b s ta n tia lly d iste n d e d due to large egg-m asses in th e u te ri. The eggs are e lo ng a te , a sym m e trica l, fla tte n e d on one side; th e y m easure 5 0 -6 0 |im by 2 0 -3 0 |im and are p a rtia lly e m b ry o n a te d w h e n laid. The sh ell is re la tiv e ly th ic k and colourless.
Biology and Life Cycle. The a d u lt w o rm s live fre e ly in th e lu m e n o f th e tra n s ve rs e and d e sce n d in g colon and th e re ctum (also th e caecum and th e a p p e n d ix ). M ales die o u t a fte r c o p u la tio n and fe m a le s m ay te m p o ra rily a tta ch to th e m ucosa th ro u g h u n d e rp re ssu re e xerte d by th e oesophagus. They fee d on b a cte ria p re sen t in th e stool. The fem ales, w h e n fu lly g ra vid , m ig ra te d o w n th e large in te s tin e and, a t n ig h t, cra w l o u t o f th e anus and d e p o s it th e ir eggs in th e p e ria n a l skin fo ld s. The e m b ry o n a te d eggs, covered w ith a sticky, irr ita n t
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su bsta nce , becom e in fe c tiv e w ith in a fe w h ours o f th e tim e th e y are d e p o site d . W hen eggs, c o n ta in in g in fe c tiv e larvae, are sw a llo w e d th e y hatch in th e sm a ll in te s tin e . Passing d o w n th e a lim e n ta ry tra c t th e y e v e n tu a lly e sta b lish in th e large in te s tin e area, m a tu rin g sexually.
Disease.
E nte ro biasis s e a tw o rm in fe c tio n ).
(e n te r o b io s is ,
o x y u r io s is ,
p in w o rm
in fe c tio n ,
Pathogenesis, pathology, and symptoms. T e m p orary a tta c h m e n t o f th e a d u lt w o rm to th e in te s tin a l w a ll m ay pro du ce a m ild local in fla m m a to ry response. Some p a tie n ts d eve lo p p ru ritis as a re su lt o f an a lle rg ic response to p a ra s ite ’s a n tig e n s. The g ra vid fem ales th a t m ig ra te fro m th e anus o n to th e p e ria n a l and p e rin e a l skin to o v ip o s it, p roduce c ra w lin g se n sa tio ns and itch in g . This in tu rn m ay re s u lt in scra tch in g th e area. The scra tch in g m ay lead to in fla m m a to ry reactions, secon d ary in fe c tio n s and even s c a rific a tio n in ch ro n ic in fe c tio n s . In sm a ll girls, th e w o rm s m ay in va de th e vagina, a fte r le a ving th e re ctu m , th e re b y p ro d u c in g irrita tio n . In th e m a jo rity o f in fe cte d persons (m o s tly c h ild re n ) th e re is no o th e r clin ic a l evidence o f th e in fe c tio n . A b e rra n t in fe c tio n s (o c c u rrin g ve ry rarely) in clu de : fa llo p ia n tu b e s in fe c tio n , o va ria n in fe c tio n , u rin a ry b la d d e r in fe c tio n , pelvic p e rito n itis , o r g ra n u lo m a o f th e liver. The w o rm s, how eve r, d ie s h o rtly a fte r re a chin g th o se lo ca tio n s. The p in w o rm in fe c tio n m ay in flic t in so m n ia and a g ita tio n in a d u lt p a tie n ts. C h ildren loose w e ig h t th ro u g h reduced a p p e tite and m ay sh o w h y p e ra c tiv ity , g rin d in g o f te e th , a b d o m in a l pain, o r v o m itin g . Epidemiology. The s u s c e p tib ility to p in w o rm in fe c tio n decreases w ith age. The m o st vu ln e ra b le are ch ild re n o f pre scho o l and e arly school age. The p ara site is th e m o st p re v a le n t in th e co u n trie s o f th e te m p e ra te c lim a tic zone w h e re e s tim a te d 500 m illio n people are in fe cte d . A single fe m a le p roduces som e 10 000 eggs. The eggs, covered by a sticky su bsta nce are easily tra n s fe rre d by hand, u n d e rw e a r, to w e ls o r bed sheets. The eggs easily g et a irb o rn e e ith e r th ro u g h lin e n m o ve m e n ts or are so m e tim e s d ire c tly in je cte d in to th e a ir by w o rm fe m a le s d u rin g o v ip o s itio n . There are fo u r w ays o f th e p ara site tra n s m is s io n . The m o st co m m o n m eans is d ire c t a n u s -to -m o u th by fin g e r c o n ta m in a tio n . S oiled n ig h tc lo th e s are a n o th e r a n u s -to m o u th tra n s m is s io n hazard. These re la tiv e ly d ire c t sources o f tra n s fe r o f via b le eggs to th e m o u th are re sp on sib le fo r c o n tin u e d heavy in fe c tio n in an in d iv id u a l or g ro u p o f persons w h o have s im ila r h ab its. In a d d itio n , a irb o rn e eggs th a t are d islo d g e d fro m bed linens and clothes, g et in to th e m o u th o r are in h a le d , are sw a llo w e d , and p ro vid e a re la tiv e ly sm a ll n u m b e r o f w o rm s in a large g ro u p o f in d iv id u a ls in c o n ta c t w ith th e c o n ta m in a te d air. A fo u rth m e th o d is re tro in fe c tio n , in v o lv in g h a tc h in g o f th e e m b ry o n a te d eggs a fte r th e ir d e p o s itio n in th e p e ria n a l area and s u b se q u e n t m ig ra tio n back in to th e re ctu m and large in te s tin e . H o m o sexu a l men, th ro u g h th e ir sexual b e h a vio u r, m ay in tro d u c e som e
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a d d itio n a l p in w o rm -in fe c tio n hazards fo r th e m se lve s. There are no re se rvo ir hosts o f p in w o rm .
Diagnosis. This is m ade by recovery o f th e c h a ra c te ris tic eggs o r th e p a ra site fe m a le s (Fot. 6.2). They are u su a lly d e te cte d in Scotch ta p e (ce llo p ha n e tap e ) p re p a ra tio n s a p p lie d to th e p a tie n t’s p e ria n a l re gion in th e e arly m o rn in g p rio r to th e p a tie n t's b a th in g o r u sin g th e to ile t. Eggs m ay be also fo u n d in th e stools, b u t th is is e xce p tio n a l, as th e fem ales o rd in a rily do n o t o v ip o s it u n til th e y leave th e in te s tin a l tra c t. The eggs are fla tte n e d on one side, and th is fla tte n in g and co n s e q u e n t re d u c tio n in d ia m e te r, plus th e th ic k e r tra n s p a re n t shell, helps to d iffe re n tia te th e m fro m h o o k w o rm eggs.
Strongytoides stercoraiis (Bavay, 1876) Stiles et Hassal,
1902 th re a d w o rm
Geographic Distribution. C o sm o p o lita n (m a in ly tro p ic a l and s u b tro p ic a l c o u n trie s ).
Morphology. associated w ith
This fa c u lta tiv e p a ra site is p ro ta n d ro u s fe m a le w h ile h o st and d io e cio u s w h ile fre e livin g . The p a ra s itic m ale is
u n k n o w n . P arasitic fe m a le s are th re a d -lik e , 2.1-2.7 m m lo n g by 3 0 -4 0 p m . The c y lin d ric a l o e so p ha g us e xte n ds th ro u g h th e a n te rio r th ird o r tw o -fifth s o f th e body. The ca udal e x tre m ity is p o in te d , and th e anal o p e n in g is s itu a te d m id v e n tra lly , a s h o rt d ista n ce in fr o n t o f th e ca ud a l tip . Paired u te ri, o vid u cts, and o va ria n tu b u le s e xte n d a t rig h t angles fro m th e s h o rt vu lva , one m e m b e r o f th e p a ir g o in g to w a rd s th e a n te rio r, th e o th e r to w a rd th e p o s te rio r end o f th e body. The eggs are th in -s h e lle d and resem ble h o o k w o rm eggs in a ppearance and size (th ey m easure 5 0 -5 8 p m by 3 0 -3 4 p m ). They are ra re ly seen in a sm u ch as th e y e m b ry o n a te and h atch in th e m ucosa o f th e sm a ll in te s tin e . F irst-stage rh a b d itifo rm larvae are 1 8 0 -3 8 0 p m lo n g by 1 4-20 p m w id e . They have a s h o rt buccal canal and a p ro m in e n t g e n ita l p rim o rd iu m . Infe ctive , th ird -s ta g e , fila rifo rm larvae are a p p ro x im a te ly 500 p m long. The ta il is n otch ed and th e ra tio o f o e so p ha g ea l le n g th to in te s tin a l le n g th is 1 : 1 . There is no sh ea th a b o u t in fe c tiv e larvae, as in th e h o o k w o rm .
Biology and Life Cycle. The fe m a le s u su a lly live in th e u p p e r p a rt o f th e sm a ll in te s tin e . The co m m o n ly p a ra sitize d levels o f th e b o w e l are d u o d e n u m and u p p e r je ju n u m , b u t all levels have been fo u n d in vaded fro m th e p ylo ric w a ll o f
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th e stom ach to th e anus, in c lu d in g th e a p p e n d ix. The p a ra s itic males, if indeed th e y exist, are e lim in a te d fro m th e bod y e arly in th e in fe c tio n . It seem s lik e ly th a t th e re p ro d u c tio n is by p a rth e n o g e n e sis o r th a t th e fe m a le is p ro ta n d ro u s h e rm a p h ro d ite p ro d u c in g s e q u e n tia lly sperm and eggs. The fe m a le s b u rro w in to th e m ucosa o f th e in te s tin a l tra c t w h e n th e y lay p a rtia lly e m b ry o n a te d eggs. The eggs u su a lly hatch in th e m ucosal e p ith e liu m , and th e e scaping firs t-s ta g e , rh a b d itifo rm larvae m ig ra te in to in te s tin a l lu m e n and th e n pass o u t in faeces to u n d e rg o fu r th e r d e v e lo p m e n t in th e soil. Infe ctive , fila rifo rm larvae m ay d eve lo p in s o il d ire c tly , or, in o p tim a l e n v iro n m e n ta l c o n d itio n s (w a rm clim ate s), th e re m ay be p ro d u c tio n o f fre e -liv in g g e n e ra tio n s th a t have b o th m a le and fe m a le w o rm s . M ore fre q u e n tly , perhaps, th e re is a single fre e -liv in g g e n e ra tio n , p ro d u c in g rh a b d itifo rm larvae, w h ic h tra n s fo rm in to in fe c tiv e fila rifo rm larvae. The la tte r are in ca pa b le o f fu r th e r d e v e lo p m e n t in th e so il and m u st p e n e tra te th e skin o f th e ir h ost to c o n tin u e th e life cycle. In fe ctive larvae o f S tr o n g y lo ld e s s te r c o r a lis , as w e ll as th o se o f h o o kw o rm s, e nhance th e ir chance o f e n c o u n te rin g h o s t skin by a g g re g a tin g in clu ste rs a t th e h ig h e s t p o in ts o f blades o f grass. On c o n ta c t w ith th e skin o f h um an beings, th e fila rifo rm larvae p e n e tra te to th e s m a ll cu ta n e o u s blood vessels and are carried to th e lungs. There th e y b re ak o u t o f p u lm o n a ry c a p illa rie s in to a lve oli and m ig ra te up th e re s p ira to ry tre e to th e p ha ryn x, w h e re som e o f th e m m ay be sw a llo w e d . W h ile in th e in te s tin e th e y e n te r th e m ucosal e p ith e liu m , m o u lt tw ice , and becom e m a tu re fem ales. In cases o f a u to in fe c tio n , a ll o r som e o f th e rh a b d itifo rm larvae in th e lu m e n o f th e in te s tin e m o u lt to th e second rh a b d itifo rm stage, th e n m e ta m o rp h o s e in to in fe c tiv e fila rifo rm larvae. They m ay p roduce re -in fe c tio n by in v a d in g th e m ucosa o f th e lo w e r p o rtio n o f th e ile u m and th e colon, tra v e l via p o rta l or accessory p o rta l ve in s to th e lungs, th e n re tu rn to th e in te s tin e and m a tu re in th e m ucosa. A t o th e r tim e s, fila rifo rm larvae are passed in fre s h ly e va cu a te d sto o ls and upon c o n ta c t w ith th e p e ria n a l and p e rin e a l skin th e y cause re -in fe c tio n .
Disease. S tro n g y lo id ia s is (s tr o n g y lo id o s is ). Pathogenesis and Pathology. A lth o u g h local lesions o ccur on p e n e tra tio n o f th e larvae in to th e skin, th e se are g e n e ra lly m in o r. The in itia l p e n e tra tio n o f th e skin by fila rifo rm larvae pro voke s little or no re a ction , a lth o u g h , a t high in te n s ity o f th e in fe c tio n , th e re m ay be p ru ritu s and e ry th e m a a t th e side o f p e n e tra tio n . S e n sitiza tio n o f th e h o st by a c o n tin u e d in fe c tio n or repeated in o c u la tio n s m ay be re sp o n sib le fo r th e d e v e lo p m e n t o f an a lle rg ic response to th e p e n e tra tin g larvae. In a h ig h ly se nsitized in d iv id u a l, th e larvae m ay n o t be successful in p ro m p tly c a rryin g o u t th e ir m ig ra tio n to th e lungs. Instead, th e y m ay m ig ra te in th e skin, ca using a ty p e o f cre e p in g e ru p tio n or cu ta n e o u s larva m ig ra n s syn drom e. M ig ra tin g larvae th a t succeed in re a chin g th e lungs b re ak o u t o f th e p u lm o n a ry a lve oli, ca using sm a ll h a e m o rrh a ge s and ce llu la r in filtra tio n in to th e a lv e o li and b ro n ch io le s. The p u lm o n a ry response to larval m ig ra tio n is g e n e ra lly n o t severe, b u t m assive in fe c tio n m ay be a ccom pa n ied by
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b ro n c h o p n e u m o n ia , and larvae m ay be fo u n d in th e s p u tu m . The a d u lt fe m a le s m ay be fo u n d in a ll p arts o f th e in te s tin a l tra c t, a lth o u g h th e y are m o st co m m o n in th e je ju n u m . It is p ro b a b le th a t a u to in fe c tio n c o m m o n ly occurs in h um an s tro n g y lo id o s is . The m e ch an ism th a t p ro m o te tra n s fo rm a tio n o f rh a b d itifo rm larvae in to fila rifo rm ones w ith in th e in te s tin e is u n kn o w n , b u t it re sults in a large increase in th e w o rm burde n . If o n ly th e g a s tro in te s tin a l tra c t and lungs are in vo lved , th e c o n d itio n is re ferred to as h y p e rin fe c tio n syn drom e. Heavy in fe c tio n s can p ro du ce e xte n sive u lce ra tio n and slo u g h in g o f th e m ucosa, and fib ro s is and in fla m m a to ry in filtra tio n o f th e su b m u co sa l layers and g ra n u lo m a s s u rro u n d in g th e larvae m ay be fo u n d in o th e r a ffe c te d organs. In ch ro nic in fe c tio n , th e a d u lt w o rm s also m ay in va de th e stom ach , ca u sin g g a s tritis 46 and perhaps u lc e ra tio n . G ra n u lo m a to u s h e p a titis 47 due to th e in fe c tio n has also been re p o rte d . C hildren in fe cte d by th e o th e r S tr o n g y lo id e s species, 5. f u e lle b o r n i m ay d e ve lo p a fa ta l c o n d itio n called sw o lle n b e lly syn d ro m e (SBS)
Symptoms. The a d u lt w o rm s in th e in te s tin e m ay give rise to no d e m o n s tra b le sy m p to m s o r to m o d e ra te to severe d ia rrh o e a . A m a la b s o rp tio n syn d ro m e w ith s te a to rrh o e a 48 has been d escribed. Heavy in fe c tio n m ay in vo lve th e large as w e ll as th e sm a ll in te s tin e , and u lc e ra tio n o f th e in te s tin a l m ucosa m ay give rise to s y m p to m s su g g e stive o f d u o d e n a l u lce r o r o f u lce ra tive c o litis 49. M e le n a 50 m ay be seen, o r th e re m ay be m assive lo w e r g a s tro in te s tin a l b le e d in g w ith passage o f b rig h t red b lo od p e r r e c tu m . P atie n ts w h o have th e h y p e rin fe c tio n syn d ro m e u su a lly p re se n t w ith fever, g a s tro in te s tin a l sym p to m s, dyspnea, w h e ezin g , h a e m o p ty s is 51, cough, and w eakness. H y p e rin fe c tio n m ay lead to severe d e b ilita tio n and d e a th . W hen th e n u m b e rs o f m ig ra tin g larvae are so g re a t as to in ju re o th e r organs (liver, h ea rt, adrenals, pancreas, kidneys, ce n tra l n ervous system ) a m u ltip lic ity o f o th e r s y m p to m s m ay be present. Epidemiology. H um an in fe c tio n s are u su a lly a cqu ire d fro m fila rifo rm larvae in th e soil. Less fre q u e n tly th o s e larvae in va de via c o n ta m in a te d w a te r. Dogs and cats are im p o rta n t re se rvo ir hosts. A u to in fe c tio n m a y be re sp on sib le fo r s tro n g y lo id o s is in persons w h o have no d ire c t c o n ta c t w ith in fe ste d so il fo r years. V e rtic a l tra n s m is s io n m ay be p ossible th ro u g h m o th e r’s m ilk S tro n g y lo id o s is is q u ite o fte n a s y m p to m a tic and th e re fo re it is d iffic u lt to asses th e n u m b e r o f in fe c te d persons. It is e s tim a te d th a t a n yw h e re fro m 100 to 200 m illio n people w o rld w id e are in fe cte d . Factors p re d isp o sin g to th e in fe c tio n are n o t o n ly h o t and h u m id c lim a te b u t also lo w s a n ita tio n o f p erson a l hygiene. 46 Inflammation of the stomach. 47 Inflammation of the liver. 48 Fatty stools; the passage of fat in large amounts in the faeces. 49 Inflammation of the colon. 50 The passage of dark and pitchy stools stained with blood pigments or with altered blood. 51 The expectoration of blood or blood-stained sputum.
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S. f u e lle b o m i, th e second species o f th is genus is k n o w fro m P apua-N ew G uinea and sub-S aharan A frica w h e re it a ffe cts m a in ly yo u n g ch ild re n fo r w h o m th e source o f in fe c tio n m ay be th e ir m o th e r's m ilk.
Diagnosis. This is m ade by d e m o n s tra tio n o f th e n e m a to d e firs t-s ta g e , rh a b d itifo rm larvae in faeces. In areas w h e re S tr o n g y lo id e s and h o o k w o rm in fe c tio n s coexist, it s o m e tim e s m ay be necessary to d iffe re n tia te its larvae fro m h o o k w o rm larvae, w h ic h can hatch in s to o l sp ecim ens if e x a m in a tio n is delayed. In d o u b tfu l cases d iffe re n tia tio n o f w e ll deve lo p ed fila rifo rm larvae o f th e se parasites, o b ta in e d fro m fae ca l c u ltu re , m ay be re co m m e nd e d. Note. The various species o f the genus S tro n g y lo id e s are m orphologically sim ilar in all o f the ir developmental stages. Likewise, while the different species each have a characteristic host species, they are not strictly host specific. Therefore, species o f S tro n g y lo id e s whose natural hosts are various wild and domestic animals may at least invade the human skin, and some o f them are known to produce patent infections in man. Since species diagnosis is difficult, some o f the clinical and pathologic conditions attributed to S tro n g y lo id e s ste rco ra lis may have been caused by a d ifferent species.
Ancylostoma duodenale (Dubini, 1843) Creplin, 1845 O ld -W o rld h o o k w o rm
Geographic Distribution. S o u th e rn Europe, th e n o rth coast o f A frica , n o rth e rn India, N o rth China, Japan; th e p a ra site has been also fo u n d in n a tive P araguayan Indians, in th e h ill trib e s o f Fukien (China), and in a b o rig in e s o f w e s te rn A u s tra lia . Recently, th e m ig ra tio n o f in fe cte d persons fro m e n d e m ic areas has in tro d u c e d th is n e m a to d e in to m a n y n e w fo ci w h e re th e A m e rica n h o o k w o rm , N e c a to r a m e ric a n u s , is o r has been, th e p re d o m in a n t h um an h o o k w o rm , nam ely, so u th e rn India, Burm a, M a laysia, P hilip pine s, Indonesia, Polynesia, M icron e sia , and P ortuguese W e st A frica , b u t it is a lm o s t less co m m o n th a n N e c a to r a m e r ic a n u s in th e se lo ca litie s. The Old W o rld h o o k w o rm , A n c y lo s to m a d u o d e n a le is th e p re d o m in a n t h o o k w o rm o f man in co asta l Peru and Chile. Morphology. The a d u lt w o rm s are re la tiv e ly s to u t, s o m e w h a t cylin d rica l, s lig h tly c o n s tric te d a n te rio rly , and have a cervical c u rv a tu re so th a t th e a n te rio r end o f th e w o rm is d ire cte d d o rs o a n te ria d . The liv in g w o rm s are p in kish or cre a m y-g re y in co lo ur, are covered w ith a to u g h cu ticle , and are p ro vid e d w ith a p a ir o f la te ra l cervical p ap illa e ju s t beh in d th e circu m o e so p h a g e a l nerve ring. They have a buccal capsule c o n ta in in g tw o pairs o f te e th . M ales m easure 8-11 m m by 0 .4 -0 .5 m m , and are b ursate, w ith tw o sp icu les th a t do n o t fu se a t th e ir d is ta l ends. The m ale w o rm is p ro vide s w ith a p ro m in e n t c o p u la to ry bursa
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p o s te rio rly . W ith in th e bursa is th e cloaca in to w h ic h b o th th e re ctu m and g e n ita l canal open. Females m easure 10-13 m m by 0 .5 -0 .7 m m , th e y have a c o n o id a l p o s te rio r end, w ith a s u b te rm in a l, v e n tra lly disposed, anal o p e n in g . The vu lva is s itu a te d m id -v e n tra lly a t th e b e g in n in g o f th e d is ta l th ird o f th e body. The tw o o va ria n tu b u le s are in tric a te ly coiled back and fo rth o ver th e in te s tin a l tra c t, th e a n te rio r one in th e m id d le th ird o f th e body, th e p o s te rio r one in th e d is ta l th ird . The ovaries a t th e ir d is ta l ends are c o n tin u o u s w ith th e s h o rt a tte n u a te d o vid u cts, each o f w h ic h in tu r n opens in to its se m in a l receptacle and is fo llo w e d by a re la tiv e ly s h o rt u te ru s and, fin a lly , by th e m u scu la r o ve je cto r, b efo re th e p aired tu b u le s jo in to fo rm th e s h o rt tra n sve rse va gina , w h ic h opens th ro u g h th e vu lva . The eggs are th in -s h e lle d and colourless, m e a su rin g 5 5 -6 5 p.m by 3 6 -4 0 p.m. First-stage, rh a b d itifo rm larvae th a t hatch fro m eggs are 2 5 0 -3 5 0 |im lo n g by 17 (im . They have a lo n g buccal canal and th e g e n ita l p rim o rd iu m is sm a ll and d iffic u lt to see. Infe ctive , th ird -s ta g e , fila rifo rm larvae are 6 2 5 -6 7 5 p.m long. They have a p o in te d ta il and a ra tio o f o e so p ha g ea l le n g th to in te s tin a l le n g th o f 1 : 4. The sh ea th is n o t as co n sp icu o u sly s tria te d as in N e c a to r.
Biology and Life Cycle. A d u lt w o rm s live in th e sm a ll in te s tin e . T h e ir fo o d consists e s s e n tia lly o f th e m u co us m e m b ra n e o f th e in te s tin e , fre e cells and plasm a. O w in g to th e p u m p in g a ctio n o f th e oesophagus, blood escaping fro m ru p tu re d in te s tin a l c a p illa rie s is passed u n d ig e ste d th ro u g h th e w o rm ’s in te s tin e . Eggs are shed in faeces on so il w h e re th e y e m b ry o n a te and hatch. The larvae d e ve lo p to se cond-stage rh a b d itifo rm larvae, and th e n m o u lt again in to fila rifo rm (th ird -s ta g e ) larvae. The in fe c tiv e larvae recognize m a m m a lia n hosts by sensing C 02 and are s tim u la te d to p e n e tra te by h o st skin p ro te in s . On c o n ta c t w ith th e skin, fila rifo rm larvae secure lo d g e m e n t in th e h a ir fo llicle s, or m ore co m m o n ly u n d e r sca lin g fra g m e n ts o f e p id e rm is. They u su a lly e n te r th e c irc u la tio n th ro u g h a c a p illa ry a t th e base o f a h a ir s h a ft. Then th e y are passively carried th ro u g h th e b lo o d s tre a m to and th ro u g h th e rig h t h e a rt to th e lungs, w h e re th e y b reak o u t o f th e c a p illa rie s in to th e a ir sacs. W ith o u t e sse n tia l d e v e lo p m e n t in th e lungs, th e y m ig ra te and carried up th e re s p ira to ry tre e to th e e p ig lo ttis . They pass o ver in to th e d ig e s tiv e tra c t and d o w n to th e sm a ll in te s tin e . Upon a rriv a l in th e lu m e n o f th e b ow el, larvae a tta c h to th e v illo u s tissu e , m o u lt tw ic e , and d eve lo p to a d u lts.
Disease. H o o kw o rm in fe c tio n (a n cylosto m o sis). Pathogenesis and Pathology. In p e n e tra tin g th e skin, th e h o o k w o rm fila rifo rm larvae m ay cause an a lle rg ic re a ctio n kn o w n as g ro u n d itch . In cases in w h ic h th e n u m b e r o f p e n e tra tin g larvae is great, alle rg ic re a ctio n to th e w o rm s o r th e ir m e ta b o lite s causes a p ru ritic , e ry th e m a to u s p a p u la r rash th a t m ay becom e ve sicu lar.
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W hen th e larvae b re ak o u t o f th e lu n g ca p illa rie s in to th e a lve oli, th e y cause m in u te fo ca l hae m o rrh a ge s, b u t o n ly in th e case o f m assive m ig ra tio n o f larvae s im u lta n e o u s ly p n e u m o n itis o f clin ica l grade is u su a lly produced. In c id e n ta lly, fo llo w in g in g e stio n o f th e larvae, th e y do n ot pass d ire c tly to th e in te s tin e , b u t p e n e tra te th e m ucous m e m b ra ne s o f th e m o u th and p h a ryn x c a rry in g o u t a lu n g m ig ra tio n , as in th e case o f larvae p e n e tra tin g th e skin. The syn d ro m e caused by th e se m ig ra tin g larvae has been called W akana disease in Japan. On a rriv a l in th e sm a ll in te s tin e , th e w o rm s a tta ch th e m se lve s to th e in te s tin a l m ucosa and begin to d ig e st th e p o rtio n s o f v illi th a t are sucked in to th e ir m o u th s. Blood is sucked o u t o f th e tissues, b u t g re a te r a m o u n ts o f b lo od are lo s t by b le e d in g a t sites o f a tta c h m e n t. H isto lo g ic a l changes in th e m ucosa o f th e a ffe c te d in te s tin e a pp e a r to be m in im a l. F la tte n in g or a tro p h y o f th e in te s tin a l v illi has been n ote d on occasion, b u t m ore fre q u e n tly e x a m in a tio n o f a b io p s y specim en d e m o n s tra te s a c o m p le te ly n o rm a l m ucosal p a tte rn . M a la b s o rp tio n is a p p a re n tly u n co m m o n , and m a ln u tritio n dose n o t seem to be c h a ra c te ris tic o f pure h o o k w o rm in fe c tio n in areas w h e re a good d ie t is availab le .
Symptoms. A t th e site o f e n try m e ch an ica l dam age to th e skin is m in im a l, b u t th e p e n e tra tio n o f fila rifo rm larvae causes on itc h in g se nsa tio n . The in itia l s y m p to m s o f th e W akana syn drom e, n o te d soon a fte r in g e stio n o f th e larvae, are: nausea, v o m itin g , sa liva tio n , itc h in g o f th e p harynx, and hoarseness. There fo llo w s an illness o f several d ays’ d u ra tio n c o n s is tin g o f cough, dyspnea, h y p e re o s in o p h ilia , nausea, and v o m itin g . In th e cases o f high in te n s ity o f th e in fe c tio n , larvae b re a kin g in to th e lung a lve o li m ay p roduce p n e u m o n itis . In acute heavy h o o k w o rm in fe c tio n s o f th e in te s tin e , fa tig u e , nausea, and v o m itin g occur, fo llo w e d by b u rn in g and c ra m p in g a b d o m in a l pain. D iarrhoea appears, w ith sto o ls th a t va ry fro m b la ck to red d e p e n d in g on th e a m o u n t and rate o f b lo o d loss. W eakness and p a llo r ra p id ly develop. E xtrem ely heavy in fe c tio n s , espe cia lly in in fa n ts , m ay p re sen t as m assive in te s tin a l h ae m o rrh a ge , w h ic h m ay p ro m p t unnecessary su rg e ry or m ay cause d ea th due to shock. In c h ro n ic h o o k w o rm in fe c tio n s th e sign and s y m p to m s are e ss e n tia lly th o se o f p ro fo u n d iro n -d e fic ie n c y a naem ia. In v a ry in g degrees th e re are p allor, fa c ia l and ped a l oedem a, d u ll e xpression, and listlessness o r a p a th y.
Epidemiology. Because in itia l in fe c tio n occurs th ro u g h th e skin, th e p re re q u is ite to w id e s p re a d h o o k w o rm in fe c tio n is a s ig n ific a n t p o p u la tio n fra c tio n d e fe c a tin g d ire c tly o n to th e soil, a n d /o r w a lk in g bare fe e t. A d d itio n a l fa c to rs in clu d e a p p ro p ria te a m b ie n t te m p e ra tu re , s u ffic ie n t ra in fa ll, and a loose sa nd y loam soil. D u rin g p eriod s o f h u m id ity p roduced by rain o r by m o is tu re c o n d e n s a tio n , th e in fe c tiv e , fila rifo rm larvae m ig ra te to th e so il surface, th e n th e y m ig ra te u p w a rd on grass or o th e r surfaces as h igh as m o is tu re p e rm its, and re a d ily p e n e tra te th e skin on c o n ta c t w ith any p a rt o f th e body. It is p ro b a b le th a t
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th e c o rre la tio n b e tw e e n high h o o k w o rm prevalence and open sa ndy soils is la rg ely a consequence o f such soils b e in g espe cia lly fa v o u ra b le fo r th e fe e d in g and p ro p a g a tio n o f large d u n g -b u ry in g beetles. Eggs o f h o o k w o rm s and o th e r h e lm in th s in g este d w ith th e faeces by d u n g beetles are d e stro ye d by th e c h e w in g m o u th parts, b u t in b u ry in g a sto o l, th e bee tle s p roduce a so il-fa e ca l m ix tu re th a t fa v o u rs d e v e lo p m e n t o f larvae. It is e s tim a te d th a t o ver 70 m illio n peo p le are in fe c te d w ith A. d u o d en a le , th e m a jo rity (59 m illio n ) in Asia.
Diagnosis. This is m ade by recovery o f h o o k w o rm eggs in th e faeces. In faecal sp ecim ens stored fo r m ore th a n 24 h ou rs a t room te m p e ra tu re , h o o k w o rm larvae m ay d e ve lo p and h atch . These larvae m u s t be d iffe re n tia te d fro m th o s e o f Strongyloides and fre e -liv in g nem ato de s. By physical e x a m in a tio n alone, h o o k w o rm disease is n o t d is tin g u is h a b le fro m th e a na e m ia o f m a ln u tritio n .
Necator americanus (Stiles, 1903) Stiles, 1906 N e w -W o rld h o o k w o rm
Geographic Distribution. S ou th ern U n ite d States, islands o f th e C aribbean, C e n tral A m erica, n o rth e rn S outh A m erica, C e n tral and S ou th A frica, so u th e rn Asia, M e la ne sia and Polynesia. resem ble th o s e o f Ancylostoma b u t are s lig h tly sm a lle r. The m ales range fro m 5 to 9 m m in le n gth , w h ile th e fe m a le s are u su a lly a b o u t 1 cm long. The head is s h a rp ly b e n t in re la tio n to th e rest o f th e body, fo rm in g a d e fin ite h o o k shape a t th e a n te rio r end. The buccal capsule o f Necator is arm e d w ith a p a ir o f c u ttin g plates, w h ile Ancylostoma has te e th . Eggs o f Necator closely re sem ble th o s e o f Ancylostoma, b u t th e y are
Morphology. A d u lts
s lig h tly larger, m e a su rin g 6 4 -7 6 p m by 3 6 -4 0 pm . F irst-sta g e rh a b d itifo rm larvae th a t hatch fro m th e eggs are 2 5 0 -3 0 0 pm lo n g by 17 p m . They have a long buccal canal and th e g e n ita l p rim o rd iu m is sm a ll and d iffic u lt to see. Infe ctive , th ird -s ta g e fila rifo rm larvae are 5 8 0 -6 2 0 p m long. As th o s e o f Ancylostoma duodenale th e y have a p o in te d ta il and a ra tio o f oeso p ha g ea l le n g th to in te s tin a l le n g th is 1:4. In co m p a riso n to th e firs t ones, sh ea th a b o u t th e fila rifo rm larvae o f Necator americanus is m ore co n sp icu o u sly s tria te d .
Biology and Life Cycle. The a d u lt w o rm s live in th e je ju n u m and u p p e r levels o f th e ile u m . They are a p p a re n tly a tta ch e d to th e m ucosa m o st o f th e tim e , a lth o u g h th e re is d e ta c h m e n t fo r m o v e m e n t fro m place to place d u rin g fe e d in g and m a tin g . The life cycle o f Necator americanus is g e n e ra lly s im ila r to th a t
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d escribed fo r Ancylostoma duodenale except th a t th e firs t one a b s o lu te ly re q uires p u lm o n a ry m ig ra tio n . Life span o f b o th h o o k w o rm s is d iffe re n t, A. duodenale lives 1-5 years, w h ile N. americanus m ay su rvive as lo n g as 18 years.
Disease. A m e rica n h o o k w o rm in fe c tio n (necatoriosis). Pathogenesis, Pathology, and symptoms. These are s im ila r to th o se d escribed fo r Ancylostoma duodenale, how eve r, th e skin a lle rg ic re a ction p ro du ce d by p e n e tra tin g fila rifo rm larvae o f Necator americanus is m ore co m m o n . In te s tin a l s ym p to m s a pp e a r to be less co m m o n in fe c tio n s th e n in th o s e w ith A. duodenale.
in th e A m e rica n
h o o k w o rm
Epidemiology. It is g e n e ra lly th e sam e as d escribed fo r Ancylostoma duodenale. N. americanus in fe cts 384 m illio n peo p le a ll over th e w o rld . Diagnosis. This is th e sam e as described fo r Ancylostoma duodenale. Note. If humans come in contact w ith infective larvae o f the dog hookworms A n c y lo s to m a b ra zilie n se (tropical and sub-tropical areas) or A. c a n in u m (cosmopolitan, particularly frequent in the northern hemisphere) penetration o f the skin may take place, but the larvae are then unable to complete their m igratory cycle. They may evoke a fairly severe skin reaction, form ing serpiginous tunnels through the tissues, erythem atous and sometimes vesicular at the advancing end. This syndrome is referred to as creeping eruption or cutaneous larva migrans. Occasionally larvae o f N. a m e ric a n u s may also migrate in the skin producing creeping eruption, but it has shorter duration and smaller dimensions in comparison w ith th a t produced by A. brazilense. Incidentally species o f hookworms other than mentioned are also capable o f producing cutaneous larva migrans syndrome in man (U n cin a ria ste n o c e p h a la , the European hookworm o f dogs, B u n o s to m u m p h le b o to m u m , the hookworm o f cattle and zebu, and others). Human intestinal infections w ith the cat hookworm, A n c y lo s to m a c e y la n ic u m have been reported in South and Southeast Asia.
Trichiuris trichiura (Linnaeus, 1771) Stiles, 1 9 0 V 2 w h ip w o rm
Geographic Distribution. C o sm o p o lita n , espe cia lly p re v a le n t in w a rm , m o is t regions o f th e w o rld .
Morphology. The co m m o n nam e o f th e p a ra site (w h ip w o rm ) has been coined b a sing on th e o v e ra ll a ppearance o f its b o th sexes. Its a n te rio r tw o -th ird s 5 2
52 In some elaborations the worm is described with its synonymous name as Trichocephalus trichiurus.
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are th re a d -lik e , th a t m akes th e m resem ble a w h ip . M ales are 3 0 -4 5 m m long, w ith coiled p o s te rio r ends. The m ale g e n ita lia co n sist o f a lo n g sacculate te stis, vas deferens, and e ja c u la to ry tu b u le , w h ic h e m p ty in to th e cloaca. Females are 3 5 -5 0 m m , w ith s tra ig h t p o s te rio r ends. The fe m a le g e n ita lia co nsist o f a single sacculate ovary, o v id u c t, and u te ru s, w h ic h co n s tric ts as it jo in s th e va gina , w h ic h in tu rn c o n tin u e s as a s e rp e n tin e tu b u le to th e vulva, w h ic h lies v e n tra lly a t th e a n te rio r e x tre m ity o f th e fle s h y p o rtio n o f th e w o rm . A d u lts have long, slender, w h ip -lik e a n te rio r ends, and th ic k e r, s h o rt p o s te rio r ends. The oeso p ha g us is a sle n d e r tu b e s u rro u n d e d by cells (stich o cyte s) c o lle c tiv e ly te rm e d a stich o so m e . Eggs are 5 0 -5 5 p m by 2 2 -2 4 p m and b a rre l-sh ap e d and, in a d d itio n to a v ite llin e m e m b ra ne , have a trip le shell, th e o u te rm o s t o f w h ic h is b ro w n . They also have b ip o la r, u n sta in e d , in tra la m in a r p ro m in e n ce s th a t have th e a ppearance o f m u co id plugs. Eggs are u n e m b ry o n a te d w h e n passed.
Biology and Life Cycle. A d u lt w o rm s live a tta ch e d to th e w a ll o f th e caecum , and less co m m o n ly to th e w a ll o f th e a p p e n d ix, colon, o r m o st p o s te rio r level o f th e ile u m . Females are o vip a ro u s. Eggs are disch arg e d and passed in th e faeces. M o is tu re is e sse n tia l fo r th e ir fu r th e r d e v e lo p m e n t. In fe ctive eggs c o n ta in firs t-s ta g e larva o f th e p arasite . W hen th e y are in g este d, larvae em erge in th e s m a ll in te s tin e and m ig ra te to th e large in te s tin e w h e re th e y d e ve lo p to m a tu rity . M an is th e o n ly kn o w n n a tu ra l h ost o f Trichocephalus trichiurus, a lth o u g h w h ip w o rm s o b ta in e d fro m th e p ig and ce rta in m onkeys are m o rp h o lo g ic a lly sim ila r.
Disease. W h ip w o rm in fe c tio n , tric h iu ria s is (trichocephalosis, trichiurosis). Pathogenesis. The e xact m e ch an ism by w h ic h Trichocephalus trichiurus a ffe c ts th e h um an h ost is n o t kn o w n , b u t tw o processes - m e ch an ica l and a lle rg ic m ay be in vo lved .
Pathology. The a n te rio r ends o f th e w o rm s, in te rla ce d in th e co lo n ic m ucosa, a p p a re n tly p roduce little dam ag e to th e h o st unless p re se n t in large n um be rs. In p a tie n ts w ith w h ip w o rm d yse n te ry (heavy in fe c tio n s fo u n d m ore fre q u e n tly in ch ild re n ), th e m ucosa can be grossly d e m o n s tra te d to th e o e d e m a to u s and fria b le . A n a l s p h in c te r to n e is lost. The re ctu m te n d s to prolapse. This o fte n causes lin e a r b le e d in g rents in th e o e d e m a to u s m ucosa.
Symptoms. L ig ht w h ip w o rm in fe c tio n s are u su a lly a s y m p to m a tic . H eavier in fe c tio n s m ay be ch ara cte rize d by a b d o m in a l pain and d iste n sio n , b lo o d y or m u co id d ia rrh o e a , te n e sm u s, w e ig h t loss, and w eakness. Prolapse o f th e re ctum is o cca sio n a lly seen, u su a lly in ch ild re n w ith heavy in fe c tio n s . A n a e m ia and m o d e ra te e o s in o p h ilia m ay be seen in heavy in fe c tio n s .
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Epidemiology. In fe ctio n re su lts fro m s w a llo w in g th e in fe c tiv e eggs, w h ich are o b ta in e d d ire c tly or in d ire c tly fro m th e soil. W h ip w o rm is th e th ird m o st c o m m o n n e m a to d e in fe c tin g h um a n s w ith th e cu m b e r o f cases w o rld w id e o f several m illio n people. T rich o ce p h a lo sis is a ty p ic a l d irty -h a n d disease and c h ild re n are m ore lik e ly to becom e in fe cte d th a n a d u lts.
Diagnosis. This is m ade by d e m o n s tra tio n o f c h a ra c te ris tic eggs in faeces (Fot. 6.2). T ric h o c e p h a lu s eggs th a t have m uch g re a te r th a n n o rm a l d im e n sio n s are o ccasion a lly seen in h u m a n faeces. A lo n g w ith an increase in size, a b n o rm a l shape and th ic k n e s s o f th e shell have been re p o rte d in stoo ls fo llo w in g tre a tm e n t. In som e in stances such large eggs w e re id e n tifie d as th o s e o f th e dog w h ip w o rm T ric h o c e p h a lu s v u lp is .
CapiUaria phUippinensis Chitwood, Valesquez et
Salazar, 1968 Geographic Distribution. H um a n cases have been P hilip pine s, T h ailan d , Japan T aiw an, Korea, Iran, and Egypt.
re p o rte d
fro m
th e
Morphology. A d u lt m ales are 2 3 -3 .2 m m lo n g by 30 p m w id e , th e y are ch aracte rize d by v e n tro -la te ra l ca ud a l e xpa n sio ns and an e x tra o rd in a rily long, s m o o th sp icu la r sh ea th. Females are 2 .5 -4 3 m m by 47 p m and m ay co n ta in in u te r o u n e m b ry o n a te d or e m b ry o n a te d eggs and o cca sio n a lly larvae. The b o d y o f th e fe m a le is d iv id e d in to tw o a lm o s t e q u a l p arts - th e a n te rio r c o n ta in s th e o e so p ha g us and o esophageal g lands (stich o som e), and th e p o s te rio r c o n ta in s th e in te s tin e and re p ro d u c tiv e system . Eggs are 3 6 -4 5 p m lo n g by 21 p m w id e , have a s tria te d in c o n s p icu o u s p o la r p ro m in e n ce s a t each end.
shell, and
Biology and Life Cycle. A d u lt w o rm s live b u rro w e d in to th e m ucosa o f th e s m a ll in te s tin e , p re d o m in a n tly th e je ju n u m . Eggs pass fro m th e h o st in faeces. They e m b ry o n a te in w a te r and are in g este d by sm a ll fish , w ith in w h ich th e larvae hatch and m ig ra te to th e m e se n th e rie s to becom e in fe c tiv e . F ish -e a ting b ird s a p p e a r to be th e n o rm a l d e fin itiv e h o st fo r th is p arasite . H um an in fe c tio n occurs w h e n fish are eaten raw . In te rn a l a u to in fe c tio n is a n o rm a l fe a tu re o f th e life cycle in m a m m a lia n hosts.
Disease. In te s tin a l ca p illa rio sis. Pathogenesis. C a p iila r ia p h U ip p in e n s is in v a d in g th e sm a ll in te s tin e causes a m o re o r less severe e n te ro p a th y , w h ic h
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is m a n ife ste d
by d e ra n g e n e n t o f
in te s tin a l fu n c tio n w ith m a la b s o rp tio n and loss o f flu id , e le ctro lyte s, and plasm a p ro te in s in to th e in te s tin a l tra c t.
Pathology. M o s t o f th e p a th o lo g ic processes are fo u n d in th e sm a ll in te s tin e . Its w a ll is fo u n d to be th ic k e n e d and in d u ra te d , and th e surface vessels p ro m in e n t. It is d iste n d e d w ith co p io u s w a te ry flu id th a t, a t a u to psy, is fo u n d to c o n ta in a b u n d a n t larvae and a d u lts o f th e p arasite. Symptoms. The disease is in te s tin a l m a la b s o rp tio n w ith s y m p to m s o f c h ro n ic d ia rrh o e a and b o rb o ryg m u s. The d ia rrh o e a m ay be p ro tra c te d and m ay be a ccom pa n ied by a no re xia , nausea and v o m itin g , and h y p e rte n s io n . The p a tie n t m ay becom e cachetic, w ith gen e ra lize d anasarca. In clin ica l p ic tu re o f th e disease h y p o n a tra e m ia , h ypocalcaem ia, m a rked h yp o ka la e m ia , and h y p o a lb u m in a e m ia have been describe d , as w e ll.
Epidemiology. In te s tin a l in fe c tio n is a cqu ire d by e a tin g disease. In th e P h ilip p in e s one s a la d ” c o n s is tin g o f ve ge ta b le s
ca p illa rio s is is p re su m a b ly a zoonosis. H um an ra w fre s h w a te r fish in e n d e m ic areas o f th e o f th e ty p ic a l sources o f in fe c tio n is “ ju m p in g and a v a rie ty o f live a q u a tic anim als, in c lu d in g
s h rim p
Diagnosis. This is m ade by fin d in g th e n e m a to d e eggs in faeces.
Anisakis simplex Rudolphi, 1809 h e rrin g w o rm
Geographic Distribution. C o sm o p o lita n (m a in ly m a rin e co astal areas). Morphology. A d u lt A n is a k is s im p le x , o ccu rrin g o n ly in th e sto m a ch s o f m a rin e m a m m a ls m ay reach th e le n gth o f 10 cm (fe m a le s) and 7 cm (m ales). T h ird -s ta g e larvae (L3) encysted in th e fle sh o f th e ir in te rm e d ia te - o r p a ra te n ic hosts are re g u la rly coiled, w h itis h and se m itra n s p a re n t, and covered w ith a th in e nvelope. T h e ir le n g th is up to 20 m m . T h e ir m o u th is su rro u n d e d by th re e lips and a b o rin g to o th . T h e ir ta il is ta p e rin g to w a rd s a p ro tru s ib le process called m u cro n . Id e n tific a tio n o f n e m a to d e s re p re s e n tin g th e fa m ily A n isa kid a e is based on th e s tru c tu re o f th e a n te rio r p o rtio n o f th e ir a lim e n ta ry tra c t (visible th ro u g h s e m itra n s p a re n t bod y w a ll in live- o r dead and a rtific ia lly cleared specim ens). A n is a k is can be d is tin g u is h e d by its s-shaped v e n tric u lu s (g la n d u la r s tru c tu re b etw e e n o e so p ha g us and th e in te s tin e ) and th e lack o f any o e so p ha g ea l or in te s tin a l processes.
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Biology and Life Cycle. D e fin itiv e m a m m a l hosts o f A n is a k is , such as d o lp h in s , w h a les, seals, and p orpoises e xpel u n e m b ry o n a te d eggs o f th e p arasite to th e w a te r. Eggs s in k to th e b o tto m w h e re firs t-s ta g e larva(Li) is fo rm e d (w ith in th e egg). It m o u lts in to second stage larva (L2) and hatches. The larva, covered w ith a p o s t-m o u lt sh ea th, sw im s fre e ly in th e w a te r fo r up to 2 w eeks. W ith in th a t p e rio d it m ay be eaten by its firs t in te rm e d ia te host, crustacean o f th e o rd e r E uphausiacea (o th e rw is e kn o w n as k rill). Infe cte d e u p h a u s iid s are eaten by p la n c tiv o ro u s fis h (such as h errin g), th e second in te rm e d ia te hosts, w h e re th e p a ra site encysts in th e p e rito n e a l ca vity or w ith in th e tissues, in c lu d in g m u s c u la tu re . A lte rn a tiv e second in te rm e d ia te hosts (or p a ra te n ic hosts) m ay be ce p h a lo p o d s o r large p re d a to ry fis h fe e d in g on in fe cte d p la n c tiv o ro u s fis h . The th ird -s ta g e larvae (L3), p re sen t in fis h host, are a t th is p o in t in fe cte d to m am m als, in c lu d in g h um ans. W hen in g este d, th e y becom e a c tiv a te d by stom ach ju ice s and, u sin g its b o rin g te e th , p e rfo ra te th e m ucosa o f sto m a ch or in te s tin e . A fte r som e tim e th e y m o u lt b e co m in g fo u rth -s ta g e larvae (L4) and m o u lt again b e co m in g a d u lt n em ato de s. H um ans are a ty p ic a l hosts and th e re fo re th e parasite s never m a tu re and e v e n tu a lly d ie o ut. Disease. A n isa kid o sis (p e rta in in g to th e disease caused by any o f th e species b e lo n g in g to th e fa m ily A nisakid a e). Pathogenesis, Pathology, and symptoms. The
larva, p e rfo ra tin g th e stom ach m ucosa in flic ts an in fla m m a to ry response. The s y m p to m s m ay occur w ith in 4 -2 4 hours a fte r e a tin g fis h w ith via b le larvae. There are th re e m a jo r g ro u p s o f s y m p to m s o f a n isa kid o sis: g a s tro in te s tin a l, g a s tro a lle rg ic and “ A n is a k is h y p e rs e n s itiv ity ” . The g a stric s ym p to m s in clu d e : e p ig a stric pain, nausea, v o m itin g , etc. w h ile in te s tin a l lo ca tio n o f th e p arasite s trig g e rs fe a tu re s in d ic a tin g in te s tin a l p s e u d o -o b s tru c tio n and / o r acute a bd o m e n . S om etim es th a t presence o f th e n e m a to d e larvae can be associated w ith d e rm a to lo g ic m a n ife s ta tio n s (u rtic a ria , a ng io e d e m a ) or rarely a na p h yla xis. “ A n is a k is h y p e rs e n s itiv ity ” is a te rm a p p lie d in th e s itu a tio n s w h e re cu ta n e o u s a n d /o r a n a p h yla ctic s ym p to m s are n o t associated w ith g a s tro in te s tin a l sym p to m s. As a consequence o f p ro lo n g e d e xposure th e parasite s m ay cause localised g ra n u lo m a ta o r even m assive, e o s in o p h ilic h a e m o rrh a g ic, tu m o u r-lik e g ro w th s . The s y m p to m s o r a n isa kid o sis are n o t sp e cific and th e re fo re , in th e past, th e re have been cases o f m is d ia g n o s in g th is p a ra sito sis by c o n fu s in g it w ith som e o th e r c o n d itio n , such as sto m a ch ulcers or a p p e n d ic itis .
Epidemiology. T h ird -sta g e larvae o f A n is a k is s im p le x can be fo u n d in m a rin e fis h and ce ph a lo po d s (squid, o cto p u s etc.) all over th a t w o rld . They have been recorded fro m over 150 fish species, b u t it seem s o b vio u s th a t p ro b a b ly any fis h (or ce p h a lo p o d ) can be its second in te rm e d ia te h o st o r p a ra te n ic host. The fa c to r lim itin g th e occurrence o f th o s e w o rm s is th e w a te r s a lin ity . Because
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e u p h a u s iid crustaceans, liv in g so le ly in fu ll-s a lin ity ocean w a te r, are th e only kn ow n fir s t in te rm e d ia te hosts, it m akes it d iffic u lt fo r th e p ara site to in vade fre s h w a te r o r b ra c k is h w a te r areas. The B altic h e rrin g can o n ly in fe c t th e m se lve s w h ile m ig ra tin g to D anish S traits. S im ila rly fre s h w a te r p re d a to ry fish like sander can in fe c t th e m se lve s w h ile m ig ra tin g to th e sea in search fo r fo o d . The m a jo rity o f Anisakis larvae are rem oved in th e process o f fish e v is c e ra tio n (g u ttin g ). Som e sm a ll p ercen tag e o f th e m re m a in s in th e fle sh . This is espe cia lly e v id e n t fo r p re d a to ry fis h . E ating ra w o r u n d e rco oke d fis h (sushi, sa shim i, g ru ne h e rrin g e etc.) m ay by a source o f in fe c tio n . Also in a d e q u a te sa ltin g , m a rin a tin g , o r (cold) s m o k in g m ay n o t in a c tiv a te th e larvae. A p ro lo n g e d fre e z in g b e lo w -21°C is suggested to k ill th e parasites.
Diagnosis. The s y m p to m s o f a n isa kid o sis m ay be u se fu l in cases w h e re c o n s u m p tio n o f in fe cte d fis h is suspected. B lood e x a m in a tio n fo r e o s in o p h il levels can also be u seful. D irect c o n firm a tio n o f an Anisakis in fe c tio n can be a cqu ire d th ro u g h endoscopy. M o d e rn te c h n iq u e s in vo lve im m u n o -g e n e tic m e th o d s (e.g., IgE im m u n o b lo ttin g ; PCR)
4.2. The tissue nematodes Trichinella spiralis sensu iato (Owen, 1835) Raillet, 1895 tric h in a w o rm
Taxonomy. Recently, a p p lic a tio n o f m o le c u la r te c h n iq u e s in ta x o n o m y a llo w e d d iv id in g Trichinella spiralis sensu la to in to fiv e d is tin c t species (T. spiralis sensu s tric to , T. nativa, T. britovi, T. pseudospiralis, and T. nelsoni). Geographic Distribution. C o sm o p o lita n . Morphology. The m ale is 1.4-1.6 m m long, th e fe m a le is 3 -4 m m . The body is sle n de r and th e oeso p ha g ea l p o rtio n is n o t m a rk e d ly n a rro w e r th a n th e p o s te rio r p a rt. In b o th sexes th e m o u th bears a p ro tru s ib le s ty le t. The h in d end o f th e m ale bears a p a ir o f la te ra l fla p s on e ith e r side o f th e d o a c a l o p e n in g w ith tw o pairs o f p a p illa e b e tw e e n th e m . There is n e ith e r a sp icu le n o r a sh e a th . In th e fe m a le th e v u lva is s itu a te d n ear th e m id d le o f th e o e so p ha g ea l re g ion . The re p ro d u c tiv e tra c t is fille d w ith d e v e lo p in g eggs and larvae. In b o th sexes, th e oeso p ha g us consists o f a th in , n a rro w tu b e su rro u n d e d by a co lu m n o f g la n d u la r cells called stich o cyte s . The eggs m easure 4 0 by 30 ^ m and c o n ta in fu lly deve lo p ed e m b ryo s w h e n in th e u te ru s o f th e fem ale.
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Larvae, p ro du ce d by th e a d u lt fe m a le , m easure 100 |im long by 6 p.m in d ia m e te r. In fe ctive larvae in m uscle tis s u e are 0 .8 -1 .0 m m long.
Biology and Life Cycle. A fte r c o p u la tio n has ta ke n place in th e in te s tin e th e m ales die and th e fem ales p e n e tra te in to th e m ucosa. There th e y pro du ce eggs th a t hatch in sid e th e u te ru s o f th e w o rm . The released larvae, a fte r p e n e tra tin g th e in te s tin a l w a ll, m ig ra te th ro u g h th e ly m p h a tic vessels to th e b lo o d s tre a m and are d isse m in a te d to va rio u s tissu e s and organs. They m ay becom e lodged in va rio u s lo ca tion s, in c lu d in g th e m yo ca rd iu m , brain, c e re b ro s p in a l flu id , and bod y ca vities, fro m w h ic h th e y la te r re -e n te r th e blood stre am and fin a lly reach th e s tria te d m uscle w h e re th e y becom e enca p sulate d w ith in th e fib re . The m uscles o f th e lim b s and d ia p h ra g m are th e m o st c o m m o n ly in fe c te d , fo llo w e d by th e to n g u e , m asseter, in te rc o s ta l, e xtra o cu la r, laryngeal, and p a ra v e rte b ra l m uscles. A ll m a m m a ls m a y be in fe c te d w ith th e se larvae, b u t pigs and rats are th e m o st im p o rta n t re se rvo ir hosts in N ature. H um ans a cq u ire th e in fe c tio n by in g e s tin g raw , o r in a d e q u a te ly cooked, m e a t th a t co n ta in s encysted larvae o f th e p arasite . T h e ir capsules are d isso lved by g a stric ju ice , and th e larvae are released in to th e d u o d e n u m or je ju n u m , w h e re th e y m o u lt fo u r tim e s and becom e a d u lt w o rm s. Disease. T richin o sis. Pathogenesis. The p rim a ry p a th o g e n ic e ffe c t o f T ric h in e H a s p ir a lis com es fro m d e s tru c tio n o f th e s tria te d m uscle fib re s in w h ic h it encysts. V a s c u litis m ay a ccom pa n y th e m ig ra tio n o f th e larvae, a cc o u n tin g fo r th e s p lin te r h ae m o rrh a ge s and p erhaps th e p e rio rb ita l oedem a. C ertain o f th e n e u ro lo g ica l m a n ife s ta tio n s o f tric h in o s is m ay also be due to va scu litis. D eath o f a TrichineHa p a tie n t m ay g e n e ra lly be blam ed to m yo ca rd itis, e n ce p h a litis, or p n e u m o n itis .
Pathology. P ath o log ic changes are se ld om seen d u rin g th e in te s tin a l phase. D u rin g th e phase o f m u scu la r in va sion , a m uscle b io psy m ay sh o w p e riv a s c u la r or p e rifib rilla r in fla m m a tio n . The p ara sitize d m uscle fib re s m ay also s h o w m y o fib rilla r lysis and d isa pp e ara n ce o f th e n o rm a l s tria tio n s . M uscle fib re s a d ja c e n t to in fe cte d m yo fib re s are u su a lly u n a ffe c te d b u t m ay becom e a tro p h ie d o r h y a lin ize d . A capsule fo rm s a ro u n d th e parasite , as a re su lt o f p ro life ra tio n o f e n d o m y s ia l re tic u lu m o r in te rs titia l co n n e ctive tissu es. The capsule is g ra d u a lly s u rro u n d e d by lym p h o cyte s, e o sin o p h ils, m acrophages, and fo re ig n bod y g ia n t cells, w ith g ra n u lo m a fo rm a tio n . The e n tire cystic s tru c tu re is g ra d u a lly replaced by fib ro u s tissu e and becom es ca lcifie d. The m o st co m m o n fa ta l c o m p lic a tio n is in te rs titia l m y o ca rd itis, caused by m ig ra tin g larvae th a t d e g e ne ra te or com e ca lcifie d in h ea rt tissu e . The lesions in th e m y o ca rd iu m sh o w d e g e n e ra tio n , necrosis, and c a lc ific a tio n .
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A n o th e r fa ta l c o n d itio n is m e n in g o e n c e p h a litis . The b ra in m ay sh o w oedem a and co n g e stio n o f th e m eninges, p e riva scu la r in filtra tio n in th e V irc h o w Robin spaces, e n d o th e lia l p ro life ra tio n , th ro m b o s is , and p e te ch ia l h ae m o rrh a ge s.
Symptoms. In th e in te s tin a l phase o f tric h in o s is th e p a tie n t m ay be a s y m p to m a tic o r m ay sh o w tra n s ie n t g a s tro in te s tin a l sy m p to m s such as nausea, v o m itin g , d ia rrh o e a , c o n s tip a tio n , o r a b d o m in a l pain. The fo u r ca rd in a l fe a tu re s o f th e m u scu la r phase are fever, m yalgia, p a lp e b ra l oedem a, and e o s in o p h ilia . O th e r less co m m o n sy m p to m s in clu d e headache, flu s h in g o f th e face, c o n ju n c tiv itis 53, p ru ritu s , d ia p h o re s is 54, a no re xia , and th irs t. Lym ph nodes fre q u e n tly becom e e nlarged and te n d e r. Dam age to m uscles m ay cause d iffic u lty in eye m o ve m e n t, b re a th in g , ch ew ing , s w a llo w in g , and speech, o r in th e use o f th e e x tre m itie s . The m o st co m m o n cause o f d ea th is m y o c a rd itis 55, w h ic h m ay a p p e a r as e arly as th e second w e e k b u t m o re o fte n a fte r th e th ird w e e k if th e in fe c tio n . E n c e p h a litis56, m e n in g itis , b ro n c h o p n e u m o n ia 57, and n e p h ritis 58 m ay also cause d e a th ; th e y d e ve lo p b e tw e e n 4 th and 6 th w e e ks o f th e in fe c tio n .
Epidemiology. W h ile b o th a d u lts and encysted larvae o f T ric h in e lla s p ir a lis d evelop w ith in th e sam e host, tw o hosts are re q u ire d to c o m p le te th e life cycle. There are th re e p rin c ip a l m a in te n a n ce cycles: •
pig to pig, in areas w h e re th e cu sto m o f fe e d in g h o u se h o ld garbage to pigs is w id e s p re a d ;
• •
rat to rat, in th e presence or absence o f a p p re cia b le in fe c tio n in pigs; sylvatic, p e rp e tu a te d by ca rn ivo u rs o r o m n iv o ro u s w ild hosts.
In N ature, in fe c tio n is th o u g h t to be co m m o n ly p ro p a g a te d by th e black rat (iR a ttu s r a t t u s ) and th e b ro w n ra t (/?. n o r v e g ic u s ), w h ic h are c a n n ib a lis tic . Pigs, w ild boars, bears, cats, dogs, and o th e r m a m m a ls th a t e at fle sh becom e in fe c te d . The so called urb an tric h in e llo s is in vo lves th e cyclin g o f th e p ara site b etw e e n rats, pigs, and h um an s. Infe cted dead o r m o rib u n d rats are eaten by pigs. The pigs w ith T ric h in e lla larvae encysted in th e ir m uscles are in g e ste d (raw o r u n d e rco o ke d ) by h um ans, u su a lly in th e fo rm o f sausage or o th e r c u s to m a rily eaten ra w m eat. It is e s tim a te d th a t in th e USA alo ne th e a n n u a l n u m b e r o f cases is a b o u t 150 to 300 th o u s a n d , w ith o n ly 150 clin ica l cases re p o rte d . A p ro lo n g e d d e e p -fre e zin g o f p o rk m ay k ill th e larvae, a lth o u g h n e m a to d e s are kn o w n to be able to su rvive ce rta in p erio d s o f fre e z in g (d o w n to -15°C). The u p p e r te m p e ra tu re lim it is +77°C and th e m e e t m u s t be cooked u n til is n o t p in k 53 Inflammation of the conjunctiva. 54 Perspiration, especially profuse perspiration. 55 Inflammation of the muscular walls of the heart. 56 Inflammation of the brain. 57 Inflammation of the lungs which usually begin in the terminal bronchioles. 58 Inflammation of the kidney.
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any longer. (S a nita ry re g u la tio n do n o t a llo w tric h in a -in fe c te d m e e t to be d ire cte d to th e m arket.) The th re a t o f T ric h in e lla in fe c tio n has been th e m ain reason b e h in d th e to ta l ban on p o rk in som e cu ltu re s and re lig io n s. It is th e re fo re e v id e n t w h y Jews and M o sle m s are fre e o f T ric h in e lla in fe ctio n s.
Diagnosis. This is u su a lly based on clin ica l s ym p to m s and h is to ry o f in g e s tio n o f p o o rly cooked m eat, espe cia lly p o rk p ro d u cts. S erologic te s ts are u s e fu l59. A lth o u g h m uscle b io psie s are n o t u su a lly p e rfo rm e d to d e te c t larvae, th e p ro ce d u re m ay be used. W h ile larvae are o cca sio n a lly fo u n d in th e blood and c e re b ro s p in a l flu id and b o th a d u lt w o rm s and larvae can be d e te cte d in stools, th e lik e lih o o d o f m a k in g a d ia gn o sis by th e se m eans is sm all. O th e r la b o ra to ry fin d in g s , such as e o s in o p h ilia and le u kocyto sis, m ay also serve as in d ic a to rs fo r tric h in o s is . In a d d itio n , ele vate d serum m uscle enzym es, such as la ctic deh yd ro ge n ase , aldolase, and c re a tin in e p h o sp h o kin a se , m ay also aid in T r ic h in e lla d ia gn o sis.
Dracunculus medinensis (Linnaeus, 1758) Gallandant,
1773 G uinea w o rm , M e d in a W o rm
Geographic Distribution. A frica
(the N ile V alley, Sudan, c e n tra l and e q u a to ria l A frica and on its w e s t coast), th e M id d le East, A fg h a n is ta n , P akistan, India; cases o f h um an in fe c tio n are also kn o w n fo r Ind o ne sia (p ro b a b ly im p o rte d fro m India). The p a ra site w a s once fo u n d in Korea, as w e ll as in th e W est Indies and S outh A m erica.
Morphology. The little -k n o w n m ale w o rm is in co n sp icu o u s and 2 cm long. Its p o s te rio r end is coiled on its e lf one o r m ore tim e s. Females m easure 7 0 -1 2 0 cm long by 0.7-1.7 m m in d ia m e te r. They are e lo ng a te , cylin d rica l, b lu n tly ro u n d e d a t th e a n te rio r end, and recurved a t th e ca ud a l e x tre m ity . The o va ria n tu b u le s , o vid u cts, and u te ri are paired, and th e va gina is u n p a ire d . No v u lva has been fo u n d in g ra vid fem a le . Body ca vity o f gra vid fe m a le w o rm s is a lm o st fu lly o ccup ie d by a u te ru s d iste n d e d w ith rh a b d itifo rm larvae. The rh a b d itifo rm larvae are 2 5 0 -7 5 0 p.m in le n gth and 1 0-25 |im in d ia m e te r. The presence o f a d ig e stive tu b e and c u tic u la r a n n u la tio n s d is tin g u is h e s a D ra c u n c u lu s species larva fro m a m ic ro fila ria {v id e in fr a ) .
Bentonite Flocculation Test (BF).
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Biology and Life Cycle. W o rm s d eve lo p to m a tu rity in th e bod y ca v ity or d ee p e r co n n e ctive tissu es, and th e fem ales m ig ra te to th e s u b cu ta n e o u s tissu es w h e n th e y becom e g ra vid . A papule is p roduced in th e skin (o f a lo w e r lim b ) w h e re th e head o f th e fe m a le lies ju s t u n d e r th e d e rm is, and th is becom es v e s ic u la r and fin a lly ulcerates, e xp o sin g th e w o rm . A lo o p o f u te ru s prolapses th ro u g h th e bod y w a ll o f th e w o rm , to lie in th e ulcer o p e n in g . W hen th e u lce r is im m e rse d in w a te r, larvae are disch arg e d in large n um be rs. The m o tile larvae are q u ic k ly in g este d by v a rio u s species o f crustaceans, in c lu d in g cope p od s o f th e genus C y c lo p s , b e in g th e m o s t co m m o n in te rm e d ia te hosts o f th e p arasite . Inside th e s u ita b le copepod, th e larvae m o u lt tw ic e and becom e in fe c tiv e fo r th e fin a l host. S u b s e q u e n tly th e y becom e q u ie sce n t and sh ow no in c lin a tio n to leave th e co pepod. In g e stio n o f an in fe cte d co pe p od in u n filte re d w a te r p ro vide s o p p o rtu n ity fo r h um an in fe c tio n . On a rriv a l in th e d u o d e n u m , th e larvae m ig ra te th ro u g h th e in te s tin a l w a ll and reach th e loose co n n e ctive tissu e , u sua lly re tro p e rito n e a l in p o s itio n , w h e re th e y d e ve lo p in to a d u lts. Disease. D ra cu ncu liasis (d ra c u n c u lo s is ). Pathogenesis, Pathology, and symptoms. There are no clin ic a l s ym p to m s o f in fe c tio n u n til a gravid fe m a le m ig ra te s to s u b cu ta n e o u s tissu e . The release o f a large a m o u n t o f to x ic b y -p ro d u c ts o f a h is ta m in e -lik e n a tu re by th e w o rm causes a p ro fo u n d syste m ic re a ction , p re s e n tin g as e ryth e m a , g eneralized u rtic a ria , p ru ritu s , fa in tin g , giddness, a sth m a , dyspnea, and, o ccasionally, v o m itin g and d ia rrh o e a . A fe w h ours a fte r th e se p ro d ro m a l sym p to m s, a reddish papule, w ith a ve sicu la r ce ntre and in d u ra te d m a rg in , begins to develop, u sua lly on th e lo w e r p o rtio n o f th e leg a ro un d th e la te ra l m a lle o lu s. The p apules have also been kn o w n to a pp e ar on th e arm s, back, breasts, b u tto cks, hands, ja w , penis, scro tu m , and to n g u e , o r on th e a b d o m in a l w a ll o r in th e o rb it o f th e eye. This lesion ra p id ly d eve lo p s in to a b liste r, w h ic h ru p tu re s u po n c o n ta c t w ith w a te r. The w o rm m ay m ig ra te to th e serous o r syn o via l cavities, as w e ll as to th e e x tra d u ra l space, ca using p le u ritis 60, p e ric a rd itis 61, s y n o v itis 62, a rth r itis 63, and sp in a l e x tra d u ra l abscess. R egional ly m p h a d e n o p a th y 64 and te ta n u s se con d ary to d ra cu n cu lo sis have also been re p o rte d .
Epidemiology. It is e s tim a te d th a t, u n til re ce n tly th e to ta l n u m b e r o f cases w o rld w id e w as 3.5 m illio n . In recent years th is n u m b e r decline d d o w n to som e 160 th o u s a n d . There are tw o c ritic a l p o in ts in th e w o rm 's life cycle th a t are crucial fo r b re a k in g its life cycle and lim itin g th e n u m b e r o f cases: 1) in g e s tio n o f an in fe c te d co pe p od and 2) c o n ta c t o f an in fe cte d person w ith w a te r th a t can be 60 Inflammation of the pleura. 61 Inflammation of the pericardium. 62 Inflammation of a synovial membrane. 63 Inflammation of joints. 64 Disease of the lymph nodes.
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used fo r d rin k in g . People in th e e n d e m ic areas have been w id e ly edu ca te d a b o u t som e necessary m easures fo r a v o id in g in fe c tio n . It is re co m m e nd e d to filte r w a te r th ro u g h a clo th o r to d rin k w a te r th ro u g h a s h o rt pipe o u tfitte d w ith a piece o f clo th a t th e end. Because tra d itio n a l s te p -w e lls fa c ilita te co n ta c t o f sick people w ith w a te r, th e re have been som e e ffo rts to re-design th o se w ells. Because o f a n a rro w h ost s p e c ific ity o f o th e r d ra cu n cu lid w o rm s, none o f o th e r m a m m a ls are b e in g im p lic a te d as re se rvo ir hosts fro m Dracunculus medinensis.
Diagnosis. This u su a lly p resents no p ro b le m s in e n d e m ic areas, as th e d e v e lo p m e n t o f th e local lesion is q u ite ch a ra cte ristic. Once th e u lce r is fo rm e d , larvae m a y be o b ta in e d fo r d ia g n o s tic purposes by flo o d in g th e area w ith w a te r.
Toxocara cams (Werner, 1782) Johnston, 1916 canine ro u n d w o rm
Toxocara cati (Schrank, 1788) Brumpt, 1927 fe lin e ro u n d w o rm
Geographic Distribution. C o sm o p o lita n . Morphology. T. canis (and T. cati) are sp ecific to th e ir re sp ective canine and fe lin e hosts. T h e re fo re th e ir d e v e lo p m e n t is h um a n s is la rg ely lim ite d (the p ara site ca n n o t m a tu re in th e h u m a n o rg a n ism ). T h erefo re a d u lt m o rp h o lo g y w o u ld n o t be ve ry im p o rta n t to its d ia g n o stics. The fe m a le T. canis is 6 .5 -1 5 -cm lo n g w h ile th e m ale a tta in s th e le n g th o f 4 - 6 cm. B oth sexes have th re e d is tin c t lip s w ith d e n tig e ro u s ridges and p ro m in e n t ce rvica l alae (w in g -lik e la te ra l p ro je c tio n s ). The la te ra l h y p o d e rm a l cords are vis ib le w ith th e naked eye. No g u b e rn a c u lu m is present. In th e fe m a le th e vu lva is a b o u t o n e -th ird th e bod y le n g th fro m th e a n te rio r end. The m ale has a sin g le tu b u la r te s tis . The ovaries o ccupy a s u b s ta n tia l space in th e fe m a le body. The u te ri co n ta in up to 27 m illio n eggs a t a tim e . The eggs are m a m m illa te d , b ro w n ish , and a lm o s t spherical, m e a s u rin g 7 5 -9 0 pm . They are e m b ry o n a te d w h e n laid and ve ry re sista n t to adverse c o n d itio n s . Female T. cati can be 4 to 12-cm -long w h ile th e m ale is 5 -6 cm. The m o st d is tin c t d iffe re n c e b e tw e e n b o th species is th e size o f th e ir cervical alae.
Biology and life cycles. There are fo u r d iffe re n t p a th w a ys o f T. canis d e v e lo p m e n t: 1) in yo u n g pups up to 4 -5 w e e ks o f age, 2) in fe m a le dogs, 3) in m ale dogs, 4) in a ccid e n ta l hosts like h um ans. The life cycle in yo u n g pups resem bles ve ry m uch th a t o f Ascaris lumbricoides in hum ans. The a d u lt w o rm s
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can be fo u n d in th e in te s tin e o f pups and th is g ro u p o f hosts is th e p rin c ip a l source o f in fe c tio n fo r h um ans. M ale a d u lt dogs serve, in fa ct, as in te rm e d ia te hosts w ith th e larvae w a itin g d o rm a n t in th e ir tissues, to be eaten by a n o th e r ca rn ivore. In fe m a le dogs, on th e o th e r hand, th e larvae also becom e d o rm a n t fo r c e rta in tim e -p e rio d . T h e ir ta rg e t, how eve r, are th e fo e tu se s in th e u te ru s and th e in fe c tio n is via th e tra n s p la c e n ta l ro u te . Som e percen tag e o f larvae in th e a d u lt a n im a ls ends up in th e in te s tin e as m a tu re w o rm s. In h um ans, T. c a m s are capable o n ly o f lim ite d d e v e lo p m e n t, never re a chin g th e a d u lt stage.
Disease. To xoca riasis {to x o c a ro s is , visce ra l larva m igrans, VLM ). Pathogenesis, pathology, and symptoms. If a m an in g ests in fe c tiv e eggs o f th e s e w o rm s, d e v e lo p m e n t proceeds o n ly as fa r as th ird -s ta g e la rva e 65, w h ich a fte r a p e rio d o f m ig ra tio n encysts in th e tissu es. M a n y o f th e larvae re a ch in g th e liv e r and lungs, p a rtic u la rly th e liv e r re m a in th e re . A fte r an u n d e te rm in e d p eriod o f m ig ra tio n th e y becom e e m b ed d ed in a m a trix o f e p ith e lia l cells and e n ca p su la te d in dense fib ro u s tissu e . O thers m ig ra te o r are passively tra n s p o rte d in th e blo od to e sse n tia lly a ll m a jo r o rgans o f th e body, in c lu d in g th e b ra in and eye, w h e re th e y rem ain a ctive fo r u n d e te rm in e d p eriods, m o v in g fro m place to place. The sp e ctru m o f h u m a n to xo c a ro sis com prises several sym p to m s, th e firs t d escribed o f w h ic h are visce ra l larva m ig ra n s (VLM) and o cu la r to x o c a ro s is (ocular larva m ig ra n s - OLM). VLM syn drom e, g e n e ra lly re p o rte d fro m ch ild re n , in clu de s feve r, w h e e z in g and cough, e nlarged liver, le u k o c y to s is 66, and p ro n o u n ce d e o s in o p h ilia , as w e ll as h y p e rg a m m a g lo b u lin e m ia 67. O cular to xo ca ro sis o fte n occurs a m o n g te e n -a ge rs or yo u n g a d u lts. The m o st p ro m in e n t s y m p to m is a fa ilin g vis io n a lo n g w ith a fu n d u s mass. In th e se cases p e rip h e ra l e o s in o p h ilia is u su a lly la c k in g 68. An a sso cia tio n b etw e e n T o x o c a ra s e ro p o s itiv ity and a sth m a has been suggested. Epidemiology. The p rin c ip a l source o f in fe c tio n fo r h um ans, p a rtic u la rly ch ild re n are yo u n g dogs and cats. Those a n im a ls becom e in fe cte d tra n s p la c e n ta lly by th e ir m o th e rs. T h erefo re p e rio d ic d e w o rm in g o f canine and fe lin e house pets is re co m m e n d e d as w e ll e d u c a tio n o f people on th e life cycles o f th e parasites, hygiene, and a n th e lm in tic tre a tm e n t schedules. (Please n o te th a t d e w o rm in g o f p re g n a n t dogs and cats is n o t re co m m e nd e d.). It has been In eggs of Toxocara cants, as in other ascarids, including Ascaris lumbricoides, two moults have been noted, so the infective is third-stage larva of this nematode, not the second-stage one. 66 A transient increase in the number of leukocytes in the blood. 67 An excess of gamma globulins in the blood. 68 The laboratory diagnosis of larval toxocarosis is possible on the basis of serologic tests, usually with use of the ELISA assay. On the other hand, sera of patients infected with another nematode Trichinella spiralis often cross-react at low dilutions with toxocaral antigen in this test, so some results of immunoenzymatic examination for toxocarosis may be false positive, particularly at low titers. For this reason, there is necessity of verification of weakly positive results in the ELISA test using more sensitive method, such as Western blot analysis.
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assum ed th a t in urb an areas ch ild re n in fe c t th e m se lve s w h ile p la yin g in sand boxes open fo r g eneral pub lic. Such fa c ilitie s are c o m m o n ly used by stra y cats as th e ir to ile ts . T h erefo re it is su ggested th a t sandboxes sh o u ld be covered w h e n n o t in use.
Diagnosis. C linical m a n ife s ta tio n o f VLM o r OLM sh o u ld be an in d ic a tio n o f p ossible Toxocara in fe c tio n . D ia g n o stic to o ls a va ila b le fo r d e te c tin g Toxocara larvae in clu d e : o p h th a lm o s c o p ic e x a m in a tio n , ELISA or RIA, and b io psy in som e cases.
Exercises 1.
Explain th e fo llo w in g conce p ts: fa c u lta tiv e p arasite, p a ra te n ic host, a u to in fe c tio n .
2.
List th e n e m a to d e s th a t have so il-b o rn e in fe c tiv e stages.
3.
W hich n e m a to d e species are capable o f a u to in fe c tio n o f th e ir host?
4.
W hich n em ato de s, d escribed above, occur o n ly in tro p ic a l co un trie s?
5.
W hich o f th e n e m a to d e s d escribed above are o vo vivip a ro u s?
6. P oint th e d ire c tio n o f A s c a ris lu m b r ic o id e s m ig ra tio n in h um an o rg a n ism . W hich b lo o d vessels w e re m arked w ith arrow s?
7.
Label th e fo llo w in g d ia g ra m w ith h a b ita ts o f in d iv id u a l d e v e lo p m e n ta l stages o f T ric h u ris t r ic h iu r a :
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8.
On th e d ia g ra m b e lo w la b el d e v e lo p m e n ta l stages o f S tr o n g y lo id e s s te r c o r a lis :
References M arked, E. K., Voge, M., John, D. T. 1992: M e d ica l P arasitology. W. B. S aunders Co., P hila d e lp h ia , London, T o ro n to , M o n tre a l, Sydney, Tokyo. Beaver, P. C., Jung, R. C., Cupp, E. W . 1984. C linical P arasitology. Lea 8i Febiger, P hila d e lp h ia .
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