EPIDEMIOLOGICAL STUDIES ON JAPANESE ENCEPHALITIS IN KYOTO CITY AREA, JAPAN III. SEASONAL PREVALENCE OF VIRUS INFECTIONS IN SEVERAL PIG POPULATIONS SHOWN BY VIRUS RECOVERY FROM ENGORGED CULEX TRITAENIORHYNCHUS SUMMOROSUS

When vector mosquitoes engorged by feeding on pigs are tested for virus recovery after incubation for 7 to 10 days, the results may show mosquito infection itself. Therefore, seasonal prevalence of infection in each pig population can be estimated from course of the infection rate among mosquitoes. Many mosquitoes of the main vector of Japanese encephalitis virus, Culex tritaeniorhynchus summorosus, collected by light traps everyday or every other day in some pig sheds from 1967 to 1970 were tested for virus recovery after incubation. The tests were positive during about a month period each summer, and the peak infection rate was high being over 10%. The course of the mosquito infection showed a certain pattern with one or two peaks between the initial recovery and the highest peak. From the interval of 12 to 13 days after the first recovery to the peak, cyclic infection between the pig and the mosquito may occur at the same interval.