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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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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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