RELATIONSHIPS OF MOSQUITO VECTORS TO WINTER SURVIVAL OF ENCEPHALITIS VIRUSES

Abstract

In tests of 140,538 Culex tarsalis collected in Kern County, California in the years 1950 to 1955, 208 strains of Western equine encephalomyelitis (WEE) virus and 162 strains of St. Louis encephalitis (SLE) virus were isolated. The monthly pattern of WEE virus isolations correlated closely with the feeding activities of C. tarsalis. When blood feeding was minimal (November 15 to January 15) no virus was found. Strains isolated from January through March had characteristics of attenuation or low titers. The findings suggest the possibility of an avian host wintertime reservoir of infection as an alternative to a mosquito vector winter reservoir. The occurrence of SLE virus in C. tarsalis was limited to June through September, except for one isolation in March. The peak incidence of SLE infection was in August in marked difference to the May to July peak for WEE virus.