Quantitative experiments on the vector capability of Culex (Culex) univittatus Theobald with West Nile and Sindbis viruses.

Mosquitoes from a laboratory colony of Culex theileri originating from material collected at Lake Chrissie in the Eastern Transvaal, South Africa, were given infective blood-meals consisting of four l0-fold graded doses of either West Nile or Sindbis viruses. Transmission of virus by individual mosquitoes to individual chicks was attempted from 14 to 20 days after the infective feed. Soon after attempted transmission mosquitoes were tested individually for virus. For West Nile virus it was found that 1.5 logs of virus were necessary to infect 10% of the mosquitoes and 8 out of 50 infected mosquitoes transmitted the virus. For Sindbis virus the value determined for the 10% infection threshold was 2.0 logs while 2 out of 23 infected mosquitoes transmitted the virus. These results indicate that C. theileri is a potential vector of limited efficiencybut it is suggested that this species is probably responsible for some of the human infection by each virus which occurs in the highveld region of South Africa.