An Outbreak of Human Tularemia Associated with the American Dog Tick, Dermacentor Variabilis

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Abstract
Summary During May, June, and July 1964, 12 cases of tularemia were diagnosed in South Dakota, all on the Pine Ridge and Rosebud Indian Reservations. Epidemiologically, the outbreak was characterized by its involvement of Indian children with a mild form of the ulceroglandular type of tularemia. Field investigations revealed unusually great tick activity. Nine of 52 lots of American dog ticks, Dermacentor variabilis, collected from vegetation and domestic animals were positive for Pasteurella tularensis. A high percentage of sera from dogs and horses was found to have tularemia agglutination antibody titers. The occurrence of these cases in an area relatively free of tularemia in the past was a result of a sharp elevation in the population of arthropod vectors. The American dog tick was established as the principal vector of the disease. Common exposure to large tick populations located in the heavily vegetated pine ridges and river valleys explains the unusual epidemiologic pattern of infection.