Human Encephalitis in the Yakima Valley, Washington, 1942

In the Yakima Valley, Washington, a series of four annual epidemics of encephalitis have occurred. The present report is concerned with the last of these outbreaks (1942), which is the third studied and reported. The findings of this investigation warrant reporting, particularly since the cases were followed more carefully clinically, since a higher proportion of both early and late phase serums were obtained for neutralization tests, and especially since 49 virus isolations were made from mosquitoes caught in the epidemic area. Identification of these viruses and repeated titrations of antibody in the patients' serums have greatly delayed this report, but during the interval certain other significant data have been collected and experiments performed which contribute greatly to the analysis of the problem. Furthermore, it may now be recorded that two succeeding summers (1943-1944) have passed during which there has been no encephalitis epidemic in the valley. Only 1 human case