Naoko Nihei

Analysis of Northern Distribution of Aedes albopictus (Diptera: Culicidae) in Japan by Geographical Information System

Abstract Aedes albopictus (Skuse), a mosquito vector of the dengue fever virus, is prevalent in Japan, distributed widely in Honshu Island with its northern limits between latitude 38° to 40°degrees north. The factors affecting distribution of the species in the northern part of Japan were studied using the geographical information system (GIS). During 1998–2000, larval surveillance was carried out in 26 urban and rural areas in the Tohoku district, in the northern part of Honshu Island, by collecting larvae from artificial and natural habitats. Climatological analysis, using the GIS, showed that the following conditions accounted for the current distribution of Ae. albopictus: an annual mean temperature higher than 11°C and a mean temperature of the coldest month, January, higher than −2°C. A period with temperature above 11°C in the confirmed area of the mosquito successively continues for more than 186 d per year. The accumulated temperature calculated from a temperature of 11°C, which may be close to the developmental zero of Ae. albopictus, was over 1,350 degree-days. The relationship between the beginning of short-daylength, inducing egg diapause, and the monthly mean temperature during September and October necessary for successful larval development in the Tohoku district is also discussed. We also show the relationship between the current distribution of Ae. albopictus and the annual mean temperature in the United States. From these results it is predicted that Ae. albpictus will be established in some cities in northeast United States.

A MARK-RELEASE-RECAPTURE STUDY ON DISPERSAL AND FLIGHT DISTANCE OF CULEX PIPIENS PALLENS IN AN URBAN AREA OF JAPAN

ABSTRACT A mark–release–recapture of Culex pipiens pallens was conducted in an urban area of Japan during June 26–29, 2007. Larvae naturally occurring in rain gutters were collected and reared to adults in a laboratory. A total of 10,183 emerging female Cx. pipiens pallens of 4–8 days old were marked with fluorescent dye and released from one site. Recapture was made on 4 consecutive days using 41 Centers for Disease Control and Prevention traps with 1 kg of dry ice and human landing collection, and 121 marked females were recaptured. The overall recapture rate was 0.01. The mean distance traveled by the recaptured females was estimated as 470, 287, 326, and 517 m on days 1–4, respectively. The maximum flight distance of host-seeking Cx. pipiens pallens was estimated as 1,217 m based on the relationship between distance from the release site to the collection site and the total number of recaptures/traps. The population size of female Cx. pipiens pallens in the study area was estimated as 100,904 ± 8,509. The size of operational area for the control of Cx. pipiens pallens in urban area is discussed.

Analysis on the Dispersal Pattern of Newly Introduced Latrodectus hasseltii (Araneae: Theridiadae) in Japan by Spider Diagram

Abstract The dispersal pattern of the widow spider Latrodectus hasseltii (Araneae: Theridiadae), in Osaka Prefecture, Japan, was analyzed from accumulated survey data of spider distribution. All confirmed infested points from 1996 to 2002 were plotted on a map, and infested points in each survey year were connected with the nearest previously confirmed points. Expansion patterns of the confirmed habitats were analyzed by year and dispersion distances were classified by using spider diagram, one of method of geographical information system spatial analysis. L. hasseltii moves by walking step by step on the ground, mainly in coastal areas during early stages of infestation, and also can be conveyed over distances by various vehicles, mainly in inland areas. These analyses show L. hasseltii does not move by ballooning.

Retrospective search for dengue vector mosquito Aedes albopictus in areas visited by a German traveler who contracted dengue in Japan

A German traveler developed dengue fever in late August 2013, following a direct flight from Germany. Autochthonous dengue virus (DENV) infection has not been reported in Japan. To evaluate the risk of autochthonous DENV transmission in Japan, the authors performed a retrospective search of the five areas visited by the German patient to determine the population density of dengue vector mosquito, Aedes albopictus. The annual mean temperature of each area was higher than 12°C, which is considered suitable for the establishment of A. albopictus populations. Our retrospective search revealed the population density of A. albopictus to be high in the urban areas of Japan.

Comparative Phylogenetic Studies on Schistosoma japonicum and Its Snail Intermediate Host Oncomelania hupensis: Origins, Dispersal and Coevolution.

Background Schistosoma japonicum causes major public health problems in China and the Philippines; this parasite, which is transmitted by freshwater snails of the species Oncomelania hupensis, causes the disease intestinal schistosomiasis in humans and cattle. Researchers working on Schistosoma in Africa have described the relationship between the parasites and their snail intermediate hosts as coevolved or even as an evolutionary arms race. In the present study this hypothesis of coevolution is evaluated for S. japonicum and O. hupensis. The origins and radiation of the snails and the parasite across China, and the taxonomic validity of the sub-species of O. hupensis, are also assessed. Methodology/Principal Findings The findings provide no evidence for coevolution between S. japonicum and O. hupensis, and the phylogeographical analysis suggests a heterochronous radiation of the parasites and snails in response to different palaeogeographical and climatic triggers. The results are consistent with a hypothesis of East to West colonisation of China by Oncomelania with a re-invasion of Japan by O. hupensis from China. The Taiwan population of S. japonicum appears to be recently established in comparison with mainland Chinese populations. Conclusions/Significance The snail and parasite populations of the western mountain region of China (Yunnan and Sichuan) appear to have been isolated from Southeast Asian populations since the Pleistocene; this has implications for road and rail links being constructed in the region, which will breach biogeographical barriers between China and Southeast Asia. The results also have implications for the spread of S. japonicum. In the absence of coevolution, the parasite may more readily colonise new snail populations to which it is not locally adapted, or even new intermediate host species; this can facilitate its dispersal into new areas. Additional work is required to assess further the risk of spread of S. japonicum.

Establishment of a GIS monitoring system for schistosomiasis japonica in Kofu, Japan

Abstract Although the incidence of human infection with Schistosoma japonicum in Japan fell to zero in 1977, the threat of the possible re-emergence of the disease caused by this trematode still exists. Surveillance of the parasites intermediate host, Oncomelania nosophora, in Kofu basin therefore began in 1996. A simple, new method for monitoring O. nosophora in an at-risk area in Kofu, which is based on a geographical information system (GIS), was established. At each monitoring site (of which there were 120 from 1996 until 2000, and 60 from 2001 until 2003), the O. nosophora in two quadrats, each measuring 25 × 25 cm, were collected. During the study, the exact location of each site was determined using a hand-held global-positioning system (GPS). This allowed all the sites to be digitally mapped, so that anyone with a hand-held GPS could and can reach each site. The snail and location data were processed using commercial GPS/GIS software packages and used to create a risk map for schistosomiasis re-emergence. Although all snails collected between 1996 and 2003 were uninfected, the proportion of investigated sites in which O. nosophora was detected increased from 36.7% in 1996 to 56.7% in 2003. The mean number of O. nosophora collected per snail-positive site fluctuated widely, between 8.2 and 57.4, in each calendar year. Over the study period there appeared to be a shift southwards in the areas with high densities of O. nosophora. The present results indicate that it is possible to utilize a GIS-based method for the long-term monitoring of the possible re-emergence of schistosomiasis japonica in Japan.

Fixed-point observation of Oncomelania nosophora in Kofu Basin—establishment of monitoring system of schistosomiasis japonica in Japan

There are still many Oncomelania snails that inhabit the Kofu Basin, Yamanashi Prefecture, Japan, which had been declared free of schistosomiasis japonica. Due to the need to monitor the situation, a fixed-point observation system using GIS from GPS is being examined. In addition, in broad present or former endemic areas, survey areas are being managed by remote sensing with satellite images or aerial photographs. A simple and effective monitoring method by mobile GIS using PDAs was developed, risk or hazard maps were prepared and a system that would enable a response in the event of reemergence is being examined.

Predicting the Start of the Aedes albopictus (Diptera: Culicidae) Female Adult Biting Season Using the Spring Temperature in Japan

Abstract Aedes albopictus (Skuse) (Diptera: Culicidae) is distributed widely and is common in much of Japan. In Japan, female adults begin to bite in between April and June, except in the southern subtropics where the mosquito has no dormant period. It is difficult to estimate the first Ae. albopictus biting day because it varies annually depending on the location. Over several years, we surveyed the mosquitoes at different locations that covered a range of warmer to cooler areas of Japan. We found an association between the timing of first biting day by Ae. albopictus and spring temperature. In spring months, the strongest correlation was found with mean April temperatures, followed by March. Based on these data, it may, therefore, be possible to apply a simple formula to predict the timing of the first biting day at various geographical locations in Japan. Forecasting maps were created using a simple prediction formula. We found that the first biting day for Ae. albopictus changed depending on early spring temperatures for each year.There was an approximate 20-d difference in first biting day between years with warmer and cooler springs. This prediction model will provide useful insight for planning and practice of Ae. albopictus control programs, targeting larvae and adults, in temperate regions globally.