St. Louis encephalitis in McLeansboro, Illinois, 1964.

Abstract

An epidemic of St. Louis encephalitis occurred during the summer and fall of 1964 in McLeansboro, a rural village of Hamilton County in southern Illinois. Attending physicians clinically diagnosed 22 cases, including 2 deaths, as encephalitis. Serologic evidence of SLE infection was obtained in more than half of the cases. In a survey to determine the prevalence of inapparent infection among residents, 32 of 615 donors had both HI and CF St. Louis virus antibodies in their sera. Over half of the mosquito pools, each containing approximately 25 Culex pipiens complex mosquitoes, yielded SLE virus. Altogether, there were 40 such positive pools. Tests to determine the identity of riiosquito bloodmeals indicated that the majority had fed on birds. Tissues from 3 house sparrows, a chimney swift and a catbird yielded strains of SLE virus. Surveillance for arbovirus activity in McLeansboro has continued since the 1964 outbreak.