Isolation of Japanese encephalitis virus from mosquitoes collected in Omura District, Nagasaki Prefecture, Japan, in 1964.

Isolation of Japanese Encephalitis virus from mosquitoes collected at Kuromaru village in Omura city Nagasaki prefecture had been made on May 26th thru October 13th 1964. The total 19 arboviruses could be isolated from 13442 in 144 pools of Culex tritaeniorhynchus mosquitoes, and no virus isolation from other species. Nineteen isolations had been identified as Japanese Encephalitis virus. Considering the occurrences of encephalitis cases during several years in Nagasaki prefecture, rabbits, free from Japanse Encephalitis virus infection, had been arranged at seven places selected to be exposed to mosquitoes. The information of Japanese Encephalitis virus dissemination in investigated area, especially in north and southwest area in Nagasaki prefecture, could be found from the evidence of antibody response of rabbit sera in haemagglutination-inhibition and from the evidence of Japanese Encephalitis virus isolation from mosquitoes. Japanese Encephalitis virus dissemination, however, have to be investigated by area and by stage during preand post-epidemic season for the ecological study of Japanese Encephalitis virus. Introduction The available evidence has supported that, during epidemic periods, Japnese Encephalitis (JE) viruses have been transmitted to human being and animals by the mosquitoes of Cule% tritaeniorhynchus which play significant role of virus dissemination. The ecology of JE virus, however, is not yet clear; where JE virus can survive during interepidemic periods, where the mosquitoes can obtain their virus and whether or not JE virus is disseminated among human being and animals yearly or only during epidemic which have occurred at varing and unpredictable intervals. There are many investigations of the JE virus Contribution No. 475 from the Research Institute of Endemics, Nagasaki University. * The present address is Epidemiological Department, Research Institute of Endemics Nagasaki University. 156 K aoru HAYAsm, Kumato MIFUNE, MATSUO} Hirotoshi KAWASOE, and isolation from Cule% tritaeniorhynchus mosquitoes in Kanto, Osaka, Fukuoka, Nagasaki and Okinawa in Japan and in foreign islands of Taiwan. From the results of these investigations, the period and efficiency of JE virus isolation quite varied from year to year. However, it does not seem to be caused only by the variation in number of offspring or collection of the mosquitoes as previously described (1965). On the stand point of epidemiological view, attention has being focused on the possible forecast of the spread of JE virus dissemination on the basis of isolation of the viruses from mosquitoes prior to an Ichiro MOTOMURA*, Sachiko Koichi FUTATSUKI epidemic among human being. However, for the exploration of biological infection with JE virus in nature including the problems of overwintering of JE virus, it is important matter to investigate more in details as to how the variation of periods and efficiencies in JE virus isolation caused. The present study has been undertaken to obtain the information of JE virus dissemination during epidemic season 1964, in Nagasaki prefecture. The results obtained will become to be established the foundation for the future reseach plan. Material and Method The area for survey : As shown in Fig. 1 and 23 the area selected for the 1964 collecting program was Kuromaru village which face a bay to the west and is located slightly north of Omura city, almost the middle point in Nagasaki prefecture. Kuromaru village was selected because it was isolated from other villages and located in the middle of wide rice and vegetable field. Moreover, every farmer has run many cows, catties, pigs and chicken raising as side jobs. Population of domestic animals in this village which is suspected to be exposed tomosquitoes are shown in Table 1. It.is noticeable fact that 321 pigs had been born during from January thru October 1964 and 200 of them except adult female one had been transfered to other place for sale. Collection of mosquitoes : Mosquito collection was performed on May 26th thru October 13th 1964. After sunset until midnight and sometime in the early morning before sunrise^ pigs, cows and fowls sheds were visited periodically, resting mosquitoes were picked up with an aspirator with the aid of flashlight and transfered into holding cages. Anesthetized mosquitoes with CO2 gas obtained from dry ice were classified as soon as possible with the aid of glass of 20 magnification. The classification of mosquitoes were carefully undertaken; only mosquitoes which could be definitely identified were selected and pooled into glass tubes not exceeding 100 in number. These specimens of mosquitoes Table 1= Population of Domestic Animalin Kuromaru Village (25th. Oct. 1964) A nimal born from 1st January 1964 on ward Domestic animal Japanese black cattle Adult 25 Milkcow I 53 ! 19(-ll) Pig Fowl Rabbit Dog Cat Goat Sheep 60 320 312(-200) 34 Total 29 61 172 354 0 2 2 13C-6) 22 | 28 o i o ! o 3 0 1 3 D ove ! 0 j Remarks ; The Numbers of parenthesis denote the numbers of transferee! animals from survey station to other area. Isolation of Japanese Encephalitis Virus from Mosquitoes Collected in Omura District, Nagasaki Prefecture, Japan, in 1964. Fig 1. Outline of Nagasaki Prefecture and the Survey Station <2 0. HiRAD'cT CTFY D)V Q(