Ontario. NIG. 2W1, Canada. ABSTRACT: The duration of Borrelia burgdorferi infectivity in white-footed mice. (Peroinyscus leucopus) experimentally inoculated.
Journal
of
%%‘E!dlmfe i)ise’ases,
DURATION
OF BORRELIA
WHITE-FOOTED IXODES FIELD
MICE
FOR
SCAPULARIS
THE
UNDER
CONDITIONS
L. Robbin Lindsay,1 Douglas Campbell4
BURGDORFERI TICK
1997.
33(4),
© \VildIife
1)isease
INFECTIVITY
I’I’#{149} 766-775
Ass,xiati(,n
1997
IN
VECTOR
LABORATORY
AND
IN ONTARIO
Ian K. Barker,2
Gordon
A. Surgeoner,1
Scott
A. McEwen,3
and
G.
Department of Environmental Biology, Ontario Agricultural College, University of Guelph, Guelph, Ontario N1G 2W1, Canada 2 Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario Ni G 2Wi , Canada 3 Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, Ontario N1G 2Wi, Canada 4 Canadian Cooperative Wildlife Health Centre, Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario NIG 2W1, Canada ,
mice (Peroinyscus nymphs was evalInfectivity was larvae at 7, 21, 35 and 49 days post-inoculation (DPI) or post-infestation (P1). At 7 DPI, B. burgdorferi was transmitted from 18 of 24 syringe-inoculated mice and all three tick-infected mice to 1. scapular-is larvae which fed upon them. However, at 21, 35 and 49 DPI, significantly fewer mice were infective. Borrelia burgdorfrri was isolated from tissues of 14 of 22 syringe-inoculated mice about 56 DPI, and from all three tick-infected mice. However, the level of agreement between xenodiagnosis and bacterial culture was no greater than would be expected by chance alone. We also determined if B. burgdorferi infectivity of mice varied in relation to periods of tick feeding in the field. White-footed mice were trapped during April, July and August 1993 from two habitats on Long Point peninsula (Ontario, Canada), where B. burgdorferi is endemic. Mice from each habitat were infested with laboratory-reared I. scapular-is larvae. Ticks from each mouse were subsequently examined by immunofluorescent assay for B. burgdorfrri infection and mice were cultured for B. burgdorferi. None of 3577 1. scapular-is larvae fed on 62 mice captured within the cottonwood dune habitat were infected with B. burgdorferi, although it was isolated from six of these mice. Within the maple forest habitat, 0/24, 8/21 (38%) and 1/21 (5%) mice transmitted B. burgdorferi to I. scapularis larvae during April, July and August, respectively. Most mice from the maple forest with B. burgdorfrri-positive tissues (14/21) were collected during July, although the level of agreement between xenodiagnosis and tissue culture was poor. Because B. burgdorferi infectivity in mice appears to he of short duration, overwintered 1. scapular-is larvae and nymphs may have to feed upon infected hosts at the same time of year in order for a cycle of B. burgdorferi infection to be maintained on Long Point. Infected I. scapular-is nymphs, rather than persistently infected vertebrate hosts, likely serve as the overwintering “reservoir” for B. burgdotferi on Long Point. Key wonic: Borrelia burgdorferi, epidemiology, infectivity, Ixodes scapular-is, Peromyscus lencopus. The
ABSTRACT:
leucopus) uated.
duration
experimentally
of Borrelia burgdorferi infectivity inoculated or infested with infected assessed by infesting these mice with
INTRODUCTiON
Lyme transmitted
group
ricinus
including taly
borreliosis mainly
and
derson, rnyscus
by
from
1988). leuco
1993)
of
and
of birds mammals
White-footed herein as
primary
burgdorferi
mid-western
USA
me
et
the
principal
a!.,
disease
tick,
Ixocles
Ixodes
mini
(Oliver
1985; tick et
dorfrri
is
(Bat-
when
infected
(An-
on
Godsey
et
a!.,
a!.,
in
endemic
I. scapularis
areas
nymphs
feed
reservoir-competent
hosts
(Spielman et a!., 1985). These animals come infected, and when uninfected
reserin the
scapularis
the
ticks
burgdorferi
(Lev766
larvae
acquire
and
is the black-legged formerly I. dam1993). Borrelia burg-
maintained
uninfected
1987)
vector
scapular-is,
hosts,
mice (Perodesignated
pus,
and
the
reservoir
species
“mice”) are considered voir hosts for Borrelia northeastern
infectious ticks
various
numerous Fish,
an
is
in white-footed Ixodes scapularis unfed I. scapularis
feed on them, B. burgdorferi.
is maintained
within
beI.
some of Borrelia the
wild-
LINDSAY
life dial
reservoir transmission
sequently man
et
a!.,
1985).
emerged
Recently,
that
with B. bnrgdorferi is significant in between and
through transtaticks, which sub-
infect other hosts with when they feed as nymphs
dorferi
has
population in the
nymphs
1989a, using
both
neously
Rais,
by culturing of
et
cultured
strains
hold
et
a!.,
agnostic
tissues
1985);
or
of
Mice
ini-
exposure
B.
burgdorferi
are
infective.
bacterial
by
simulta-
1987).
by
to
inand with
(BartXenodi-
culture
techniques
then used to determine the infective of mice. Anderson et a!. (1987) pro-
posed
that
after
from remain
infected infected
ganism
can
sues
of
months has
B.
acquiring
I. scapularis for life,
be
mice
collected
(4 to
6 mo
burgdorferi
nymphs,
mice
because
cultured
from
the
or-
various
during after
tis-
the
winter
nymphal
activity
vector, I. B. burgdorferi,
spirochete,
the
Long
tario, the
Point
Canada;
and endemic
(Lake
the to
Erie,
Mice
seasonal mammal
version
rates
monitored
species,
and
of
these
hosts
(Barker
et
sonal
prevalence
doiferi Long
in populations Point has not
investigated
of infection
the in
a!.,
mice
the
serocon-
have
1992),
been the
with
infected
sea-
B. burg-
of reservoir hosts been determined.
duration
the
INFECTIVITY
concept
significant
in
between of the
that the
767
co-feed-
transmission
cohorts infection
of ticks, in a geo-
on We
of B. burgdorferi in
the
were
labora-
tory. These observations led to a new interpretation of the pattern of vector-hostvector transmission in the epizootiology of B. burgdorferi infection on Long Point,
AND
METHODS
from a laboratory colony B. burgdorferi, maintamed at the University of Guelph (Guelph, Ontario, Canada) for >25 generations. Twentyfour adult mice (14 male, 10 female) each were inoculated subcutaneously between the scapulae with 0.7 to 1.6 X 10 B. burgdorferi strain LI-231. This strain originally was isolated from an engorged I. scapular-is larva from Long Point and was confirmed as B. bnrgdorferi by indirect immunofluorescent (IFA) staining with monoclonal antibody H5332 (Barbour, 1984). Each mouse then was infested with approximately 200 to 300 unfed I. scapularis larvae at 7, 21, 35 and 49 days post-inoculation (DPI). These unfed larvae were hatched from eggs deposited by females that fed on a dog (Canis familiar-is) on Long Point during April and October 1992. Three additional adult female mice each were infested with 30 1. scapular-is
obtained
for
nymphs,
antibody
which
were
to
had
fed
as
larvae
on
mice
that
syringe-inoculated with B. burgdorferi. These three mice then were infested with unfed I. scapularis larvae on the same schedule as the syringe-inoculated mice. During each infestation, mice were maintained individually in wire cages over pans of water for up to five days, and all fed larvae which
previously
dropped
off
were
mouse were plastic containers
within
environment
C
with
and Twelve
On-
42#{176}36’N, 80#{176}5’W). Although abundance of I. scapularis on
various
infectivity
scapularis, are
peninsula
be
MATERIALS
in
tick
with
may
each
ceased).
The
ing
negative
Ran-
nymphs (Mather syringe-inoculated
1993)
or
were status
1996;
a!.,
a!.,
either
I. scapularis 1990) or
larvae
techniques
(Anderson
host agent
various
et
these
inoculated
fected Mather,
vertebrate of the
infectivity in natumice has been (Mather et a!.,
(Anderson
compatible
BURGDORFERI
of B. burgdorferi and maintenance graphic locality.
concept
ricinus
and
BORRELIA
OF
infection
Ixodes
(Gern
1989b);
mice
the
in the transmission
dolph et a!., 1996). Borrelia burgdorferi rally-infested white-footed assessed by xenodiagnosis from
B. burg(Spiel-
non-systemic
co-feeding
tially
ET AL-DURATION
a to
12
14
collected.
Fed
stored
over (relative chambers
hr
light
days
at
and
later
larvae
from
damp vermiculite humidity >95%) 12 smears
24
a constant hr
dark of
cycle.
the
of
fed
larvae
were
examined
for
B.
mid-
burgdorferi by IFA staining using monoclonal antibody H5332 directed against B. burgdorferi OspA (Lindsay et al., 1991). The intensity of B. burgdorferi infection in mid-gut smears was categorized into four classes: none; few (10 per well, but 50 organisms/field at 200X). To ascertain that larvae were uninfected before feeding on experimental animals, 30 unfed larvae from each 1. scapular-is egg batch used as a source of experimental larvae were examined for B. burgdorferi by IFA staining; no spirochetes were found. Aliquots (50 p.l) of B. bnrgdorferstrain LI-231 air-dried on glass slides and fixed with gut
768
JOURNAL
OF WILDLIFE
VOL.
DISEASES,
33, NO. 4, OCTOBER
acetone served as positive controls. Up to 30 fed larvae from each of the four infestations on each mouse were examined for B. burgdorfer-i. Mice were considered infective if at least one I. scapular-is larva was infected with B. burgdorferi after feeding. Prevalence and intensity of B. burgdorferi infection in I. scapular-is larvae fed at various times following inoculation were compared statistically using the generalized linear model (Statistical Analysis System Version 6.04; SAS Institute, 1988). The general linear model also was used to compare the effect of duration of B. burgdorferi infection on infectivity of mice for larval ticks. Because of over dispersion of the data, square root transformations were performed prior to analysis. After all fed larvae had dropped from mice infested at 49 DPI, mice were euthanized by inhalation of isoflurane (Aerrane#{174}, Anaquest Division, Canada Oxygen Ltd., Mississauga, Ontario, Canada), and the urinary bladder, spleen, and left kidney were removed aseptically.
The
left
aural
pinna
from
each
mouse
was
removed and immersed in 100% ethanol for 5 to 7 mm. Each tissue was triturated in 1 ml of BSK II K-S medium, modified from Barbour’s (1984) medium by the addition of kanamycin and 5-fluorouracil (Johnson et al., 1984). One hundred and fifty .i.l of the triturate of each tissue was inoculated into a 7 ml tube of BSK II
K-S
ined
medium, by
dark
incubated field
at
33
C
microscopy
for
1, 2 and 6 wk post-inoculation (SO p.l) from each positive dried on glass slides, fixed
culture
at
and
exam-
spirochetes (pi.).
Aliquots
air10 mm at room temperature and subjected to IFA staining to confirm that the organism isolated from mice was B. burgdorferi. Mice were considered infected if B. burgdorfer was isolated from at least one tissue. The level of agreement between the xenodiagnostic and bacterial culture techniques for detecting B. burgdorferi infection in mice was determined using the kappa (K) statistic (Martin et al., 1987). In order to examine B. burgdorferinfectivity of
mice
at
various
periods
ill
were
acetone
during
the
for
tick’s
life
cycle, mice were captured on the peninsula during 20 and 21 April, and 18 and 19 August, 1993. These selected because they are periods when
few
nymphs
Long Point 4 to 6 July dates were of the year are active, 3 wk after peak and when newly-emerged lar-
nymphal activity, vae begin seeking hosts on Long Point, respectively (L. R. Lindsay, unpubi. data). Mice were collected using folding aluminum live-traps (76 X 89 X 229 mm, H.B. Sherman Traps Inc., Tallahassee, Florida, USA) placed within cottonwood (Populus deltoides) dune and maple (Acer saccha ruin) forest habitats on Long Point, described by Reznicek and Catling
1997
(1989). The abundance of immature 1. scapular-is on mice was about 40-fold greater in the maple forest than in the cottonwood dune (L. R. Lindsay, unpubi. data) and thus likely would influence the proportion of B. burgdorferi-in-
fected mice collected. Mice and ticks were similar
to
the
handled
laboratory
in a manner
studies,
except
that
mice trapped from Long Point were infested only once with laboratory-reared larvae before they were euthanized and their organs were cultured. Since unfed I. scapular-is larvae on Long Point rarely were infected with B. burgdorfer-i
(Lindsay
et
a!.,
1991),
larvae
that
were
present on mice when they were captured also were used as xenodiagnostic ticks. Thirty fed larvae collected from each mouse were dissected and subjected to IFA staining following incubation at 24 C for 12 to 14 days; the remaining proximately
fed
larvae
were
allowed
to
molt.
Ap-
2 wk after the molt, up to 30 unfed nymphs from each mouse were dissected and subjected to IFA staining. Prevalence and intensity of B. burgdorfer-i infection in ticks were determined as in the laboratory study; however, because few of the field-collected mice produced infections in feeding ticks, statistical comparisons of the effect of habitat type on these parameters were precluded. Comparison of the intensity of B. burgdorfer-i infection in fed larvae and unfed nymphs collected from the same hosts was performed using a paired t-test (P 0.05) (Snedecor and Cochran, 1989). A K value also was calculated to determine the level of agreement between xenodiagnosis and bacterial culture techniques for detection of infected mice (Martin et a!., 1987). RESULTS
The
prevalence
mice feeding
that
of
transmitted
75%
I. scapular-is (18/24 mice)
(3/22
mice)
22%
of
doiferi by
49
7 DPI,
later dorferi
DPI infected
of the infected
and DPI
(Table
were
bur-gdorferi fed
1).
larvae
one less from were 1). The
At
for
examined
to was 14%
1%
7 DPI,
B.
positive;
only about with B.
whereas collected infestations (Table
burgdorferi at 7 DPI decreased to
larvae
larvae
Borrelia
29% that larvae
fed
49
infection
were 1).
by
syringe-inoculated B.
burg-
however, of
fed
larvae
(Table
burgdorferi
was collected
observed from
I. scapularis
larvae
than 10% of infective mice positive proportion
in mice
for
at
the fed during B. burgof larvae
LINDSAY
TABL.E
ing
1.
Efficacy
infection
transmission of Borrelia in the laboratorv.
of
of
ET AL-DURATION
mice
OF BORRELIA
burgdotfen
to Ixodes
I)avs
Proportion
of
All
infective
larvae
to
larvae
onlv1
of
mice
Proportion
of
larvae
49
mice
(75)
6/23
(26)I
158/720
(22)
9/690
(1)
158/540
[8,1.01 (29)
4/22
(18)’
3/22
(14)
11/660
(2)
7/660
(1)
infective
larvae
to
infected
[11.0,0]
9/180
Tick-inoculated Proportion
follow-
times
:35
18/24
I 14,44,Olc
mice
at various
769
infected
mice
Infective
INFECTIVITY
pOSt-in(XtllatiOll
21
Syringe-inoculated of mice
larvae
SCa/)Ulafls
7
Proportion
BURGDORFERI
(5)
[7,0,01
11/120
(9)
7/90
(8)
mice
:3/3
(100)
0/3
0/3
0/3
56/90
(62)
0/90
0/90
0/90
[7,25,24J Number
positive
h One
infected
at higher
dorferi
was
0.2)
=
with
DPI
1).
TBI.F:
in
The
Borrelia
2.
relation
to
of
fed
larvae
0.001)
=
I.
greater
fed
at
B.
burg-
was when
culture
status
of
mice
of
mice
14
cate-gorv
infective
Infective
to
to
ticks
ticks”
r%Iice
Iron,
Ntimmmher
g
to svhich
of
mice
I ..seapulari.s
at least
isolated
Borrelia
burgiloiferm
miot
Borrm’Iia
burga’omfrrm
isolate(l
Mice
from
which
at
least
Omit’
noose
died
prior
to
Not
available, due
to
one
premature
mice
by
inoculated
nymphs
(Table
2).
The
larvae
at various
times
after
49
and
I. sca-
organism
inoculation,
Coltor(’ status of mice (56 I)I’I)
mice H
(+ )(I
10/10
2/10
1/10
1/10
( +)
6/6
4/6
3/6
2/6
(-)
2/2
0/It
0/li
NA
NA
0/3
0/3
(+)
mice 0/3
were
tissues one
larva/numnht’r cultured
tissue
of time infestation nmice:
recovered.
never
I. .scapularm.s
of
mice
0/4
an
death
syringe-inoculated
0/2
frommi
commipletion
sub1).
0/4
scapular-ms
infected
three
(Table
0/2
larvae
least
the
periods
0/4
I
at
to any
0/4
one
from,,
by
infective
0/2
3/3
infected
during
inoculated
0/2I
ticks
infecting
22 three
35
Tick-inoculated Infective
not
post-inoculation
Syringe-inoculated Never
of
21
7
tick-infected
termination of the experiment, B. was isolated from the tissues
for I. scapular-is at 56 1)Pt.
Days Moose
mice larvae
all
pularis
the
syringe-inoculated
were
infestation
from
ticks
infectivity
hurgdorfi’ri
B. burgdoifrri
of
sig-
on to
scapularis
At the burgdorferi
7
DPI
feeding
sequent
trans-
larvae
7
However,
other. infestation
at
compared
nymphal
intensity
within
(P
nificantly
mice.
nymphs to
infections
infes-
man].
fed
mice,
significantly by
burgdorferi
(Table
dorferi
other
each
inoculated
I. scapularis
B.
B. burggreat-
were
0.001)
not
from
mice
infected
mitted
were
different
three
=
to the
which
positive).
ink-ction class [few. ln(xk’rate. larva with B. burga’o,fen.
with
(P
compared
dates,
All
intensities
significantly
7 DPI
at
tation
(P
(percent
tested
of the infestation.
of infected ticks in each B. burgilorfei-i mice infected at least one I eapulari.s
Number 1 Infective
er
for B. burgdofrri/noioher prior to completion
(lit’(I
nn)us(’
mice
frommi
from
cultured larva
was
at each
were
of
not
mmmice tested.
each
mmiouse.
each
recovere(l
timmie’. cultured.
nsouse.
at sommie
stage
of the expenmmmemmt.
)(.
770
JOURNAL
TABLt
3.
were
OF WILDLIFE
infected
to
feeding
April,
within
1997
the maple forest habitat on Long Point the proportion of fed larvae or resulting of mice from which B. hurgdorferi was
larvae;
and the proportion
B. hurgdorferi; July and August,
with
during
VOL. 33, NO. 4, OCTOBER
of mice collected 1. scapularis
Proportion
infective
DISEASES,
of infestation
Month
of mice
infective
Proportion
of ticks
infected
Fed
to ticks
0/24
larvae
July
(0)’
8/21
0/720
August
(12)b
76/630
nymphs
49/532 0/526
Total
(9)
[8.32,9]
0/1,246
status
Numbe-r
of mice
of mice
125/1,162
6 Numnber
of infected
Nmimnbe’r
of
mice
(11)
for B. bmmrgdoefrrm/number
from
bladders,
25 kidneys. Two had B. burgdorferi sue.
Four
spleens,
ears
six mice
I. scapular-is
which
rochete of 16
to ticks
one
had
during
one
festations (Table 2). mice were infective
or
three
for
ticks
never
B. burg-
2).
The of
10
B. burgdorof the
of B.
16
pular-is
49
DPI,
the
wild
dorferi
mice on was
which
between
the
two
Long Point. Although B. burgisolated from two of 20 to 22
mice collected in each of April, July, and August in the cottonwood dune habitat, none of the fed larvae (600 to 660 per sampling interval) or resulting unfed nymphs (527 to 611 per sampling interval) exposed to pling interval fections. None the
of the
maple
infective
these mice acquired
forest for
24
adult habitat
I. scapularis
during each B. burgdorferi mice
samin-
collected
during
April
larvae.
However,
in was
cohort (P
Borrelia
ing
of fed 0.60).
was
did
larvae
Overall
eight cap-
I. sca1162 in How-
ticks from at least one
observed
burgdorfer-i
unfed from
not differ prevalence
immature (11%) of in August.
within
of immature I. scapular-is August, respectively.
mice during Tissues positive rochete vae 155)
=
fed larvae and allowed to molt
considering only were infective to spirochete
31% and
of B. burgdorferi-infecdiffered
within were
burgdorferi in fed ranged from 125 to 15 (1%) of 1158
July,
that alone.
habitats
(4)
23/66
July and August, respectively, of 21 and one (5%) of 21 mice
the same significantly
of tissues would be tive
140/3,577 [31,77,32]
many].
infection nymphs which
ever, which
proportion
(1)
tured within this habitat transmitted B. burgdorferi to feeding I. scapular-is larvae (Table 3). The prevalence of B. burgdor--
0.04) beand culture
The
(.3)
infective).
moderate,
during (38%)
=
greater than by chance
59/1,718
infected).
(percent
[fesv,
and the level of agreement (K tween xenodiagnosis at 49 DPI was no expected
(percent
(4)
[12,37,10]
3/21
in-
of these
at
(2)
81/1,859
[19,40,22]
15/1,158
feri
spi-
tissues
more
Only
of
mice tis-
one
had
larvae
class
five
and
when cultured (Table was isolated from the mice which transmitted
dorferi
feri
of 25
10/528
(14)
tested.
syringe-inoculated in more than
of the
infected
11 of 25
two
(1)
[7,6,2]
tested
examnined
infection
B. burgdomfrrm
5/630 [3,1,11
14/21
B. burgdomfrri/numnber
bnrgiloeferi/numher
B.
ticks in each
positive
recovered
of 25
with
larvae-
with
of ticks infected
Number
was
6/24d
that infected
9/66
[4,5,1]
[24,71,30]
Culture
Total
1/21 (5)
(38)
[16,39,21]c Unfed
Canada) that that became cultured,
1993.
April Proportion
(Ontario, nymphs subsequently
29 and
during
was
isolated
mice tick, July from
collected within the maple forest each sampling period (Table 3). from six mice were B. burgdorferiduring April, even though the spiwas not detected in any of the lar(n = which
July
and
180) fed
and upon
August,
unfed these
nymphs animals.
(n = Dur-
respectively,
14 of 21
and three of 21 mice captured maple forest had at least one
within the B. burgdor-
feri-positive tissue (Table 3). Borrelia burgclor-fer-i was isolated from 14 of 29 spleens, 13 of 29 bladders, eight of 29 ears
LINDSAY
and
five
of
collected
29
kidneys
on
from
more
tured
mice
one
while
of these
mice.
mice
42
both
the
B.
but did contrast,
of 66 cap-
for
and
organism
was
techniques
eight
of
of
66
(23%)
15
infect one
oniy
organs
I. scapular-is mouse infected
larvae,
yielded
yet
ticks; in feeding no B. burg-
on culture of four tissues; mouse was captured in July. There poor to moderate level of agreement
this was a
dorferi
0.35)
between
culture
xenodiagnosis
for
tions
detecting
er
recovered
from
and
(K
=
bacterial
B. bnrgdorfer-i
Regardless
of
the
most mice B. burgdorfer-i
method
of
larvae
beginning
only
7 DPI;
feeding ticks at 21, 35 and 49
ration
B.
the A
host
species
and
ing
I.
mice scapularis
munks
(Tarnias
voles
(Microtus
(Mather
et
route
were
cuniculus)
with
B.
of B. minimal The dufor on
inoculation.
field-collected
capable
ticks
of infect-
(90%)
than
(75%)
or meadow (6%)
pen
nsylvanicus)
1989b).
Rabbits
inoculated hurgdorfer-i infected larvae from 12 to 15 DPI,
agus
the
depending of
of
striatus) a!.,
during
infectivity varies
proportion
white-footed
inocula-
was DPI.
burgdorferi
I. scapularis
greater
syringe-inoculated
bacteria inoculated 1994). from
also
method
of
subcutaneously I. scapular-is but not from
4
with
B.
bu rgdorferi
to feeding I. scapular-is (Oliver et a!., 1992), and was deer
cultured 10 wk
Borrelia burgdorferi larvae that had fed
P1
from the (Luttrell
lar-
the
ears of et a!.,
was recovered on syringe-inoc-
the
inocuin-
burgdorfer-
of our
(syringe
influences
the
borreliosis the
to transmit did not
vs.
expression
in dogs
(Appel
ability of both experiand naturally-infected
B. burgdorfer-i always correlate the bacteria animals with
to feeding with the
in host tissues. B. burgdorfer-i-
infected tissues might have developed recrudescent spirochetemias at some later date, and then been capable of infecting feeding ticks, is unknown. The distinction between infected animals (culture positive) and infective fecting feeding
animals (capable ticks) should be
whenever
possible.
infectivity nodiagnostic
of hosts, based techniques,
clarify nificance
(Oryctol-
study,
rnusculus) B.
inoculation
also
study,
presence Whether
our
preMath-
infectivity was of inoculation.
(Mus
of clinical Lyme et a!., 1993).
parallel (culture
chip-
to 9 or 16 to 18 DPI (Burgdorfer, 1984). White-tailed deer (Odocoileus virginianus) were infectious vae 43 DPI
Mode
our
In
several 1987;
Ixodes r-icinus larvae than anby tick feeding (Gem et a!.,
feeding)
In
infected of in-
transmission
to
of
1993). tick
tick-in-
syringe-inoculated with et a!.,
with
larvae
upon
burgdorferi
by
fewer infected
mice
hurgdorfer from mice feeding
fected imals
fed
1990).
B.
et a!.,
I. scapular-is on
Mather,
771
P1 (McLean
is consistent (Donahue
In contrast, mice lated by syringe
ticks
experimentally were capable
I. scapular-is
period
and
INFECTIVITY
when
mentally-inoculated DISCUSSION
fecting
more
than
This studies
duration of not influenced
infec-
in mice.
tion, with
mice
mice. vious
xenodi-
4 mo
infected
fected
B. burgdor-
culture
BURODORFERI
ulated chipmunks 1993). In our study,
mice
burgdorferi-positive
not
I. scapular-is
seven
(64%)
Interestingly,
had
mice
recovered
in
negative
by
agnosis, 66
tissue
forest,
were
by
both
it was
BORRELIA
OF
became
infection
feri
Point;
than
(Table 3). At the maple
infected
from
Long
ET AL-DURATION
Clearly,
with agent or polymerase the of
course B.
studies primarily should be
identification chain and
burgdor-feri
of inmade on
the
on xcrun in
in tissue reaction), to
epidemiologic infection
sigin
mice and other hosts. On Long Point, habitat-specific differences were observed in the proportion of mice
infective
vae.
Similarly, dor-feri infection, mice varied sin
captured among (USA)
(Blanna calities varying
to
feeding
the
prevalence based on
during different (Callister
I. scapular-is
lar-
of B. burgculture, within
the same month, habitats in Wisconet
a!.,
1988);
shrews
brevicauda) captured at three in Massachusetts (USA) also capacity to infect ticks (Telford
lohad et
772
JOURNAL
OF WILDLIFE
a!., 1990). The dorferi infection cottonwood
low dune
since I. this habitat
data).
However,
dorferi from
from
not
recovery
unex-
very rare unpubi. of
B.
of six of 62 animals is evidence either that
(Burgess the maple
et
even though tick (Calhister et a!., or that contact or B. burgdor-fer-i is
a!., forest,
1986). the proportion mice
and
with was
greatest
burgdorfer-i-positive during June and
Bor-relia
captured
derson
et
bank fecting
a!.,
1987).
voles (Clethnonomys I. ncinus larvae
in Sweden also infectivity
declines Long
dorferi
in Point,
B. the
July
organs (An-
The
proportion
of
glareolus)
in-
with
B. burgdor-fer-i
infectivity
burgdor-feri decline
of mice
in
from
infectivity. B. burg-
July
(Table
these
of deer),
are
to Au-
scapular-is,
the vae
previous of the
remain
strain
in-
as whitedifferences
among
responsible
for
locali-
some
differences
of the
of
in also
in the
infection
cy-
at these
var-
et a!. (1985),
seasonal infected
season feed year, amplifies
infective
gust
for
and
the
activity nymphs prior B.
to
of 1. from the
lar-
bur-gdorferi
several
weeks
or
September.
In our study, d.or-fer-i infectivity
(Mather
but
essentially
months, and transmit B. burgdorfer-i infection to the next cohort of I. scapular-is larvae that emerges to seek hosts during Au-
sachusetts
b),
Local-
infection within mouse populations. Under this scenario, after exposure to infected I. scapular-is nymphs from May to July, mice
these values
1989a,
and
to Spielman
I.
a!.,
(Ta-
relative
(such
bur-gdor-fer-i
pattern where
on the
et
values. density,
and
age
I. fed
mice
hosts
fundamental
by feeding lower than
were Mas-
Point
observed variability. Regional variability B. burgdorfer-i infectivity of mice may
infectious vae, at the
and the infected
(29%), from
B.
likely
ed xenodiagnostic proportion of
animals reported
and
and
ed mice parently,
(14%), ticks
competent reservoir
mice
ties
Long
in tick
competent in
from
of are
experimentally-infected
variation
densities tailed
proportion larvae
1) approached
gust was unrelated to recruitment because the proportion of new individuals in the mouse population was similar in July (14%) and August (9%) (data not shown). The proportion of our mice that infectticks scapular-is
mice
on
According
mice
et
reservoir nymphs
or
inverted
of
a!., 1993). Recruitment in populations, at a time when are inactive, is likely responsible
(Talleklint
3)
The when
cle of B. bur-gclor-fer-i ious localities.
varied during the year, with in August and September
peak
for On
proportion
data). infected
infective
ble
reflect
recov-
of B. burgdorferi by culture was greatduring July. Similarly, in Connecticut the
say,
ity-specific
burg-
tissues
of B. burgdor-frr-i-infected
(USA),
unpubl.
upon
was
there is tick transmission densities are very low 1991; Lord et a!., 1994), vertical transmission of
ery est
1997
habitat
scapular-is is (L. R. Lindsay,
habitat
occurring Within
33, NO. 4, OCTOBER
scapular-is
the the
this
VOL.
prevalence of B. burgmice captured at the
in
pected, within
DISEASES,
was the
the duration of B. in experimentally-infectshort-lived same was
(
