The epidemiology of La Crosse virus in Tennessee and West Virginia

La Crosse virus (LACV) was first recognized as a cause of pediatric viral encephalitis in the upper-Midwestern United States following its isolation from a fatal case of pediatric encephalitis in 1964. From that time, LACV infections have been reported in 24 states, with the number of reported cases increasing in recent years in the Appalachian region of the United States. Two states in Appalachia, West Virginia and Tennessee have both seen a large rise in the number of reported cases in recent years. To investigate the epidemiology of the LACV infections in the eastern United States, Tennessee, and West Virginia a combination of field and laboratory studies were initiated. These studies investigated the spatial and temporal patterns of disease risk and the biology and ecosystem dynamics of both indigenous and invasive disease vectors.Four distinct regional clusters of LACV infections were detected at the national level, as well as a higher incidence risk and case-fatality rate than previously reported. The exploration into the variations of risk using different at-risk populations and geographic scales revealed the possibility of missing disease clusters resulting from performing incidence risk investigations of focal diseases using inappropriate at-risk populations and/or large geographic scales. South-central West Virginia was found to be a focus of LACV transmission and in addition to having the highest incidence risk and case-fatality rate reported in the United States. In eastern Tennessee, Aedes albopictus was found to be the most abundant mosquito collected at all sites and vegetation types, by both CO2-baited CDC trapping and human landing catches.Results from the use of variable pressure scanning electron microscopy to describe the egg of Aedes japonicus have provided more detailed information on characters of Aedini eggs, while bringing the number of more complete descriptions and micrographs of the micropyle and associated structures of the subgenus Finlaya to three. The results of these studies have provided a more complete understanding of the epidemiology of LACV and its associated vector species at both the national and state levels. These findings will help guide future research and intervention efforts to understand and prevent virus transmission.