The ecology of tularaemia.

Tularaemia, a zoonotic disease caused by the bacterium Francisella tularensis McCoy, 1912, is reported from North America, Europe and northern parts of Asia, but not from the Southern Hemisphere. Two subspecies of F. tularensis are recognised: the highly virulent type A and the milder type B, with additional subdivisions reported. Tularaemia has been reported in more than 250 animal species including man, other mammals, birds, fish, amphibians, arthropods and protozoa. Type A is reported to have a terrestrial cycle with the main reservoirs being cottontail rabbits (Sylvilagus spp.) and ticks. Type B is reported to have a mainly water-borne cycle with aquatic rodents as reservoirs, e.g. muskrats (Ondatra zibethicus) and beaver (Castor canadensis) in North America, and ground voles (Arvicola terrestris) in the former Soviet Union. In Europe, tularaemia is most frequently seen in hares (Lepus spp.) although hares probably do not constitute a reservoir for the disease. Tularaemia is transmitted by direct contact with infected animals, through contaminated water or food, or by vectors such as mosquitoes or ticks. The disease normally occurs as an epidemic, both in man and in animals, depending on the types of reservoir involved and the means of transmission at different times of the year.