Tularemia (or
tularaemia; also known as
Pahvant Valley plague,
rabbit fever,
deer fly fever, and
Ohara's fever) is a serious
infectious disease caused by the intracellular
bacterium Francisella tularensis. A
Gram-negative,
nonmotile, pleomorphic
coccobacillus, the bacterium has several subspecies with varying degrees of
virulence. The most important of those is
F. tularensis tularensis (Type A), which is found in
lagomorphs (rabbits, hares and pikas) in North America, and it is highly virulent in humans and domestic rabbits.
F. tularensis palaearctica (Type B) occurs mainly in aquatic rodents (
beavers,
muskrats) in North America and in hares and small rodents in northern Eurasia. It is less virulent for humans and rabbits. The primary
vectors are
ticks and
deer flies, but the disease can also be spread through other
arthropods. The disease is named after
Tulare County, California.