A number of parameters related to vector efficiency were investigated in the laboratory for Culex fuscocephala, a suspected Japanese encephalitis (JE) vector, and for Culex tritaeniorhynchus, a proven vector of JE virus. It was demonstrated that 97% of C. fuscocephala and 92% of C. tritaeniorhynchus became infected after ingesting very small amounts of JE virus (average infecting dose = 8 plaque-forming units (PFU/mosquito). JE virus multiplied in both mosquito species to comparable high titers (above 105 PFU/mosquito) within 10 days after the infectious blood meal. Once infected, both species maintained high virus titers through at least 4 weeks. The average transmission rates were found to be very similar in both mosquito species. Evidence suggests that virus transmission occurred after mosquito probing as well as after feeding to repletion. This demonstrates a high vector efficiency of C. fuscocephala in the laboratory as compared with that of C. tritaeniorhynchus, a confirmed JE virus vector. Together with field observations, these data provide strong evidence to incriminate Culex fuscocephala as a potentially important vector of JE virus in Thailand.
Present address: Medical Field Service School, Fort Sam Houston, Texas 78234.