Rates of infection with Japanese encephalitis virus of two culicine species of mosquito in Taiwan.

The role of Culex annulus as a Japanese-encephalitis (JE) vector has been drawing increasing attention recently. In this small trial, the rate of JE virus infection in C. annulus was compared with that in C. tritaeniorhynchus summorosus in the north-western coastal area of Taiwan, where both species are common as JE vectors. In order to increase the recovery rate of the virus, the mosquitos were artificially incubated at 26-28 degrees C for 10 days after collection. Two out of 6 C. t. summorosus pools and 7 out of 31 C. annulus pools, collected during a 17-day period in June 1969, were positive for JE virus. The results strongly suggest that one of the factors determining the severity of virus emergence in Taiwan is the total density of both species during the critical period of emergence of viraemic amplifiers: the relative prevalence of the two species of mosquito seems to be less important.