Japanese encephalitis in Sarawak: Studies on juvenile mosquito populations

In Sarawak, Japanese ncephalitis virus has been isolated almost exclusively from Culex gelidus, a mainly pig-biting mosquito, and the rice-field breeder C. tritaenior-hynchus which bites man as well as pigs (MACDONALD et al., 1965, 1967; HILL et al., 1969). Since domestic pigs have been found to become infected with the virus at a rate of about 20 % per month (SIMPSON et al., 1970) it is surmised that they, together with C. gelidus, may be mainly responsible for maintenance of the virus and that C. tri-taeniorhynchus may be mainly responsible for infections in the human population. Since the C. tritaeniorhynchus population was observed to increase significantly with the onset of the NE monsoon in September (MACDONALD 1967, HILL 1969), One object of the present visit was to study the factors involved in breeding and population changes of this species over a 12 month period. The site chosen was a Land-Dyak village (Kampong Tijirak) 19 miles south of Kuching and 1 mile from the main road. The village of some 80 houses (population 500) lay at 100 feet altitude, with hills of up to 1,000 feet close by, and other large padi fields mile away. There was a large adjoining area of old established padl field to