Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Biology and Microbiology


The World Health Organization defines an arbovirus as follows. An arbovirus must produce a viremia in one or more vertebra species, multiply in some arthropod that feeds on viremic blood and be transmitted through feeding. Ticks and mosquitoes are the main arthropod vectors that transmit this virus. The fact that the Missouri Basin states have had the post extensive epidemics of western equine encephalitis (WEE) and St. Louis encephalitis (SLE) in the country makes South Dakota an excellent area for concentrated arbovirus studies. These major environmental changes might alter the biological balance of the complex ecological factors that determine the occurrence of encephalitis to a point of contributing to future epidemic occurrences of the disease. The arbovirus activity in South Dakota among humans and domestic and wild animals is not known. A more recent mosquito survey in South Dakota. was conducted by Gerhardt in 1964 (SO). The first reported serious epidemic of WEE in the United States occurred in Minnesota, North Dakota, and South Dakota in 1941. Over 1,000 human cases and 2,500 cases of equine infections were recorded. In most of the years following 1941, South Dakota has reported a few confirmed cases of WEE infection in man and horses. An epidemic of eastern equine encephalitis (EEE) on a commercial pheasant farm in southeastern South Dakota in 1967 introduced a previously undiscovered arbovirus into the state. A preliminary survey of the mosquito vector population in the Brookings area in 1969 showed that the mosquito Culex tarsalis was one of the major species in the area. This species has been shown to be the major vector in the transmission of WEE to man and animals. The northward movement of Venezuelan equine encephalitis (VEE) into the United States necessitates a monitoring system in areas north of the VEE epidemic regions to detect introduction of the virus in these areas before an epidemic situation is created. A VEE monitoring system was established in South Dakota in 1971 following the epidemic cpizootic in Texas. The purpose of the present study was to determine the status of HEE and SLE in the human population and domestic and wild animals. The effects of irrigation on vector populations and infection indices under different environmental and ecological conditions which exist in South Dakota are discussed.

Library of Congress Subject Headings




South Dakota State University Theses



Number of Pages



South Dakota State University