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.