Culex tarsalis Coq. a Proven Vector of St. Louis Encephalitis. ∗

Summary and Conclusions

Culex tarsalis has been demonstrated to be infected in nature with St. Louis encephalitis virus and to be capable of transmitting it. Furthermore, it fits well into the epidemiological picture encountered in the Yakima Valley, Washington. We can therefore safely conclude that this species is a natural vector. This is the first instance in which a mosquito has fulfilled these 3 criteria for incrimination as a vector in respect to St. Louis encephalitis virus. C. pipiens previously has been shown to be capable of transmitting this virus in the laboratory and the same has just been demonstrated for C. coronator. In addition, these experiments demonstrate that the chicken may serve as a satisfactory reservoir of virus. This is undoubtedly shared by other birds for we have previously shown that virus may be isolated from the blood of a dove following the bite of infected C. pipiens 5 and unpublished work indicates that ducks may serve as reservoirs.