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Tularemia is a highly infectious zoonotic disease caused by several subspecies of the gram- negative bacterium Francisella tularensis (eTable 291.1).

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eTable 291.1. Francisella Tularensis Subspecies
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Francisella tularensis is a small, aerobic, nonmotile gram-negative bacterium first identified in 1911 by Dr. Edward Francis, after an outbreak of plaguelike disease in rodents in Tulare County, California. Infection has been reported in humans since 1914.2

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In the United States, nearly all human cases of tularemia are caused by F tularensis subspecies tularensis (Type A, 66%) or F tularensis subspecies holarctica (Type B, 34%).3

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Epidemiology and Pathophysiology

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Mammals provide the primary reservoir for F tularensis, including ground squirrels, rabbits, hares, voles, muskrats, water rats, and other rodents.2 Human infection typically occurs after handling infected animals or after a bite from an arthropod vector.4 In the United States, biting flies and ticks are the primary arthropod vectors. In Europe and the former Soviet Union, ticks and mosquitoes have been reported to transmit infection.2 Infection can also occur after ingestion of contaminated food or water or after inhalation of the organism from decaying animal carcasses, contaminated straw, or other sources.4 There have been several large waterborne outbreaks of tularemia in Europe and the former Soviet Union.1 The largest airborne outbreak of tularemia was reported among farmers in Sweden in the 1960s, attributed to the aerosolization of organisms from rodent-infested hay.1 There has been no documented person-to-person transmission of tularemia.4

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Infections with F tularensis are found only in the northern hemisphere. In the United States cases are reported from the eastern seaboard, Arkansas, Missouri, Oklahoma, and the central mountain regions. Other endemic areas include Eurasia, particularly the former Soviet Union, Japan, and the Scandinavian countries. Tularemia is not a World Health Organization (WHO) reportable disease. The incidence of disease is believed to have decreased significantly around the world in the past 50 years, largely attributed to the decrease in wild rabbits sold in markets and the introduction of clean water supplies.2

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In the United States, 1939 marked the peak incidence of tularemia, with 2300 cases reported that year.4 In contrast, 142 cases were reported in the United States in 2000.4 Cases have been reported in all states except Hawaii, with over 50% of all cases are reported in Arkansas, Missouri, and Oklahoma.1,3

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