The Effects of Environmental and Physiological Conditions of Culex Tritaeniorhynchus on the Pattern of Transmission of Japanese Encephalitis Virus

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Abstract
A log-probit regression was established between the infection rate of a colony of Culex tritaeniorhynchus and concentration of Japanese encephalitis virus in the mosquitoes' blood meals. The 50% infective dose of the virus for mosquitoes was 101.7 mouse ICLD50 per blood meal. A simple technique for detecting the oral secretion of virus by infected mosquitoes is described. The quantity of virus expelled by an infected the mosquito under prolonged incubation at 28°C was determined to be more than 104.0 mouse ICLD50. The interval between virus infection and initiation of virus secretion in mosquitoes was not influenced by mosquito age, concentration of sugar given to adults, history of blood engorgement in advance of infective blood meal, or history of blood engorgement following infective blood meal. A slight difference in this interval was observed among mosquitoes with different larval nutrition and those fed blood meals with different virus concentrations. However, the interval was markedly influenced by environmental temperature. Virus secretion was delayed and suppressed when infected mosquitoes were kept at 20°C. The suppression is suspected to be a consequence of the relatively slow physiological activity of mosquito tissues at low temperature rather than of a delay in the velocity of virus multiplication.