Arbovirus Studies in the Ohio-Mississippi Basin, 1964–1967

Abstract

Culex tarsalis and members of the Culex pipiens complex are important vectors of St. Louis encephalitis virus (SLE). In the western part of the United States where C. tarsalis is the primary vector, long-term observations have included nonepidemic as well as sporadic epidemic years. Before the present report and in regions where C. pipiens complex is the vector, studies were limited to outbreaks of encephalitis. This paper is based on field and laboratory studies that were focused on rural McLeansboro, Illinois, during 1964–1967 and on the metropolitan area of St. Louis, Missouri, during 1966–1967. In each of the years, SLE virus was isolated from pools of C. pipiens complex collected in both areas. At less frequent intervals, the virus was encountered in specimens from birds. Sparse rainfall and periods of sustained high temperatures were related to the SLE virus activity in mosquitoes. Although virus was regularly detected, overt disease in man was limited to 1964 in McLeansboro and to 1966 in St. Louis. Nevertheless, the potential threat of epidemics exist. This threat could be reduced through elimination of sites of mosquito-breeding by the installation of adequate treatment and transport systems for sewage.