Tularemia

Etiologic agent = Francisella tularensis

• Like Y. pestis, Francisella tularensis is a Gram (-) bipolar rod whose major reservoir is small mammals (especially rabbits and hares ["rabbit fever"], as well as squirrels, voles, muskrats, beavers, and a variety of other species).
  • Francisella tularensis infection has long been recognized as a direct zoonotic infection of rabbit hunters. They contract the organism while skinning the rabbits.
  • Tularemia is also an occupational risk for veterinarians handling infected animals, especially cats.
    • In one study in Alaska, 14% of veterinarians had positive antibody titers to F. tularensis, compared to 1% of the general U.S. population.
    • 7.7% of cases of tularemia in the U.S. between 1977 and 1998 were due to contact (bites/scratches) with infected cats, and during an outbreak in Sweden in 2000, ownership of cats was a specific risk factor for infection.
• People may also be exposed by consuming undercooked game meats (infection requires 108 organisms) or inhalation of the organism (infection requires only 101-2 organisms).
• Tularemia has also been reported to occur as a waterborne infection in Russia and Italy (The bacteria can survive for weeks to months in water and mud.), and outbreaks may be initiated when environmental conditions favor sudden increases in rodent populations, as happened in post-war Kosovo in 1999-2000.
• Like Y. pestis, F. tularensis is transmitted between infected animals in the natural setting via bloodsucking arthropods, especially ticks (Dermacentor and Amblyomma in the U.S.) and biting flies, e.g. deer flies.
  • The organism passes transovarially in ticks, thereby providing an efficient way of maintaining the organism in nature.
  • Tick transmission is also a mode of transmission to humans.
• Globally, tularemia is found most commonly in the Northern Hemisphere. In the U.S., tularemia in human beings is reported most commonly in Arkansas (23%), Missouri (19%), South Dakota (7%), Oklahoma (7%), Kansas, Montana, and Martha's Vineyard [Massachusetts]. However, during the period from 1990-2000, there were 1,368 cases reported from 44 states.
  • An outbreak on Martha's Vineyard during the summer of 2000 involved 15 cases, 11 of which were the dangerous pneumonic form. These cases were associated with employment as lawn mower operators/landscapers. A previous pneumonic tularemia outbreak had occurred on the island in 1978.