Mar 13, 2015 - Abstract. A total of 160 autochthonous dengue cases transmitted by Aedes albopictus were reported from August to October 2014 in Tokyo ...
Advance Publication by J-STAGE Japanese Journal of Infectious Diseases
Biting density and distribution of Aedes albopictus during the September 2014 outbreak of dengue fever in Yoyogi Park and the vicinity in Tokyo Metropolis, Japan
Yoshio Tsuda, Yoshihide Maekawa, Kohei Ogawa, Kentaro Itokawa, Osamu Komagata, Toshinori Sasaki, Haruhiko Isawa, Takashi Tomita, and Kyoko Sawabe
Received: December 15, 2014. Accepted: February 17, 2015 Published online: March 13, 2015 DOI: 10.7883/yoken.JJID.2014.576
Advance Publication articles have been accepted by JJID but have not been copyedited or formatted for publication.
Original Article
Biting density and distribution of Aedes albopictus during the September 2014 outbreak of dengue fever in Yoyogi Park and the vicinity in Tokyo Metropolis, Japan.
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Yoshio Tsuda*, Yoshihide Maekawa, Kohei ohei Ogawa, Kentaro Itokawa, Osamu
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Komagata, Toshinori Sasaki, Haruhiko Isawa, Takashi Tomita, Kyoko Sawabe
Department of Medical Entomology, National Institute stitute of Infectious Diseases, Toyama 1-23-1, Shinjuku-ku, Tokyo 162-8640, Japan
*Corresponding author: Mailing address: Department of Medical Entomology,
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National Institute of Infectious Diseases, eases, Toyama 1-23-1, Shinjuku-ku, Tokyo 162-8640, Japan. Tel: ＋81-3-5285-1111, 81-3-5285-1111, Fax: ＋ ＋81-3-5285-1147, 81-3-5285-1147, E-mail: tsudayso
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＠nih.go.jp
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Running Title: Vector density during dengue outbreak in Yoyogi
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Key words: Aedes albopictus; albopictus; dengue outbreak; Tokyo Metropolis; biting density;
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transmission threshold
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Abstract A total of 160 autochthonous dengue cases transmitted by Aedes albopictus were reported from August to October 2014 in Tokyo Metropolis, Japan.
Ae. albopictus is
a medically important vector of dengue virus which has been expanding its geographic distribution in temperate regions. The understanding of the distribution and density of
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biting Ae. albopictus during the dengue outbreak case in Tokyo 2014 is valuable and important to evaluate the epidemic-risk of dengue ngue fever in other highly highly populated cities
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in Europe. Of the 160 cases, 134 patients had visited a same park located in central Tokyo, Yoyogi Park. Mosquitoes infected with dengue virus were collected from this park suggesting that the place was the exclusive usive center of dengue transmission. This study aimed to collect referential data to estimate timate the transmission threshold of dengue
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virus in terms of biting density of Ae. albopictus and demonstrated high
transmission-risk areas of dengue virus in Yoyogi Park and the vicinity. The overall
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mean density of biting Ae. albopictus, 7.13/man/8 min, was sufficiently high for successful transmission of dengue virus, and areas densities higher than the areas with biting dens overall mean density were classified as high transmission-risk areas of dengue virus in
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Yoyogi Park.
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Introduction A total of 160 autochthonous dengue cases were reported from August to October 2014 in Tokyo Metropolis, Japan (1). Local transmission of dengue had been reported during the 1940s in Japan (2), but no autochthonous dengue cases have been reported thereafter for nearly 70 years. However, annual numbers of imported dengue cases has
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reached 200 in recent years (3).
The primary vector mosquito of dengue in Japan is Aedes albopictus (Skuse)
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which is distributed widely across this country (4, 5). Geographic hic distribution of Ae. albopictus has been expanding in temperate regionss since the 1980s (6), and its medical importance as a vector of chikungunya virus and dengue virus thus has been increasing in newly established areas (7). Aedes albopictus population typically shows an annual
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geometric growth from May to July, peaks in August, and then de decreases rapidly from September to November in Tokyo (8). Parks in urban Tokyo provide good habitats for
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Ae. albopictus, and the average biting density was reported to exceed 10 females/man/5min during midsummer in a certain certain park (9,10). Mark-release-recapture studies on dispersal of Ae. albopictus indicated the movement of the mosquito depends
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area where vegetation patchily on vegetation distribution within a forest or residential ar distribute in open spaces (11,12).
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The understanding of the distribution istribution and density of biting Ae. albopictus in the Tokyo 2014 took place could be valuable and area where the dengue outbreak case in T
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important to evaluate the epidemic-risk of dengue virus in other highly populated cities. The majority of dengue cases confirmed in this outbreak were linked to Yoyogi Park
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and its vicinity located in a major commerc commercial and business area in Tokyo. Of the 160 cases, 134 patients had visited Yoyogi Park aand were bitten by mosquitoes inside the park during their stay. The Bureau of Soci Social Welfare and Public Health (BSWPH) of the Tokyo Metropolitan Government collected mosquitoes in Yoyogi Park, dengue virus was detected by PCR assay(13) from some female mosquitoes in September (14). The fact clearly indicates that Yoyogi Park was the central location of dengue transmission in the outbreak in 2014. In vector control of mosquito-borne diseases, the concept of “transmission threshold (15)” or “disease risk threshold (16)”, which means 3
a threshold beyond which a vector-borne disease epidemic can arises, is important to evaluate the epidemic-risk in a particular area. We studied the distribution and density of biting Ae. albopictus in Yoyogi Park and its vicinity during the dengue outbreak to identify areas with a high risk of mosquito bites. The association between biting density of Ae. albopictus and transmission risk of dengue virus was also investigated
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through statistical analysis with the results of mosquito collection and dengue virus detection from the mosquito collected by BSWPH. The transmission threshold of
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dengue virus in terms of biting density in Yoyogi Park is discussed.
Methods
Study area: Yoyogi Park (YP: 35°40'19.11"N, 139°41'51.67"E) constitutes a large
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forest of approximately 130 ha (Fig. 1a) bordering on Meiji-Jingu Meiji-Jingu shrine (MJ: 35°40'34"N, 139°41'57"E) and the National Institution for Youth Education (NYC: 35°
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40'28.7"N, 139°41'36.4"E). For the present study, study, the entire area was examined. A large part of Yoyogi Park is covered with deciduous deciduous trees, evergreen trees, and shrubs; the shrubs in the shade provide good resting sites for Ae. albopictus. People visit
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Yoyogi Park year round for sightseeing, jogging, jogging, bird watching, exercise, etc. dense Meiji-Jingu shrine is surrounded by a de nse forest composed of evergreen
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broad-leaved trees and provides a good habitat for a variety of plants and animals (17). The western side of MJ bordering on YP aand NYC is covered densely with big trees
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and bushes, and entrance of the public is not permitted. The National Institution for educational facilities including conference rooms, Youth Education is a compound of educationa
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meeting rooms, accommodations, etc., and students staying at NYC commonly visit Yoyogi Park for exercise, training, recreation, etc. Another park, Shinjuku Centra entral Park (SCP: 35°41'23.3"N, 139°41'21.8"E),
located about 1 km north of YP, was also examined in the present study due to the report of 2 dengue patients who had visited this park and were bitten by mosquitoes at the end of August 2014. The 8.8 ha SCP is situated in a busy business and administrative area with deciduous trees and shrubs growing around the periphery. Many people daily pass through this park for commuting or walking around. 4
Mosquito collection: Human bait-sweep net collection of biting mosquitoes was carried out at YP and NYC on 4 September and at MJ and SCP on 5 September, 2014. YP and SCP was divided into 6 blocks, and 4 or 5 sites were selected for mosquito collection in each block. MJ and NYC were divided into 7 blocks each. Biting
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mosquitoes were collected in 6 or 7 sites per block in MJ and 2 sites per block in NYC. The total numbers of mosquito samples were re 30, 27, 43, and 14, in YP, SCP, MJ, and
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NYC, respectively. The location of each collection ection site is depicted for YP, MJ, and NYC in Fig. 1b. One collector was responsible for mosquito collection in a particular block and decided the location of the collection ion sites within the block uniformly. All mosquitoes attracted to the collector were captured by a sweep net (36 cm in diameter)
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for 8 min. A reliable and quicker procedure edure of mosquito samplin sampling was required in this study to provide information of spatial distribution distribution of biting mosquitoes and carry out
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the effective control of dengue transmission as soon as possible. The arrival patterns collections examined in a previous study of Aedes albopictus on a person during 30 min collectio showed that 56 and 68% of the total females females were collected during the first 5 and 10
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min of the mosquito collection, respectively (18). Thus, the time period for mosquito collection between 5 and 10 min seems enough to get a reliable estimate of biting
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density of Ae. albopictus instead of 30 min collection.
In each collection site it takes
about 5 to 7 min to transfer the collected mosquitoes to a small carrying cage by a
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sucking tube with a label distinguishing th the collection site and move to the next collection site.
Therefore, we fixed the tim time period of mosquito collection to 8 min in
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this study and tried to finish mosquito treatme treatment and movement to the next site within 7 min. In this way 4 collection sites were examined within 1 hr by one person.
The
collected mosquitoes were carried to the Na National Institute of Infectious Diseases, and counted by species and sexes. A mosquito repellent (DEET 12%) was used to protect the collectors from mosquito bites.
Data analysis:
The mean numbers of biting Ae. albopictus per collection site were
calculated and compared between YP, NYC, MJ, and SCP by ANOVA. To show places 5
with a high risk of mosquito bites, the mean number of biting Ae. albopictus was calculated for the entire Yoyogi area. Each collection site was classified into the following 5 classes based on the overall mean density and biting density of the site, N, and is represented by different colours in Fig. 1b: N = 0 (white), 0
