Quantitative Experiments on the Vector Capability of Culex (Culex) Pipiens Fatigans Wiedemann with West Nile and Sindbis Viruses1

Mosquitoes from 2 laboratory colonies of Culex pipiens fatigans originating from material collected in Johannesburg, South Africa, were given infective blood meals consisting of four 10-fold graded doses of either West Nile or Sindbis viruses. Transmission of virus by individual mosquitoes to individual chicks was attempted on the 19th or 20th day after the infective feed. Soon after attempted transmission, mosquitoes were tested individually for virus. For West Nile virus it was found that 3.9 4.7 logs of virus were necessary to infect 10% of mosquitoes and 3 of 19 infected mosquitoes transmitted the virus. For Sindbis virus the 10% infectivity threshold varied from 4.8–5.2 logs while 2 out of 6 infected mosquitoes transmitted the virus. It was concluded that C. pipiens faligans was unlikely to act as an important vector of either virus in the transfer of virus from birds to man or between human beings in the highveld region of South Africa.