Francisella (F.) tularensis is a gram-negative, pleomorphic, non-motile, aerobically growing bacillus that is very resistant especially in lower environmental temperatures.
This pathogen is the causative agent of the so-called tularaemia (rabbit fever), which is a zoonosis.
Four subspecies have been classified. Two subspecies are of particular clinical relevance: F. tularensis ssp. tularensis and F. tularensis ssp. holarctica, with F. tularensis ssp. tularensis naturally occurring in North America only and being responsible for a more aggressive course of the disease. In contrast, F. tularensis ssp. holarctica can be found in the entire northern hemisphere.
It is predominantly hares, rabbits and rodents (mice) that are affected, but also numerous other animal species, including birds, are susceptible to this pathogen. In dogs, cats and sheep, sporadic cases of illness are known. Cats suffer from the disease more often than dogs, but overall, the disease is rarely contracted.
Signs of an acute disease are apathy, fever, tachypnoea and swelling of the lymph nodes; most animals die of septicaemia within 2 weeks. Furthermore, in a chronic course, emaciation and skin ulcerations occur; in dogs and cats in addition to splenomegaly, hepatomegaly, ulcers on the tongue and icterus.
Here, too, a lethal outcome is possible after 2 – 6 weeks.
The modes of transmission include blood-sucking insects like fleas, midges, lice, ticks, etc., consumption of infected carcass/meat or contaminated water. The infectious dose is very low, only a few bacteria are sufficient (exception: infections through the gastrointestinal tract).
Humans become infected when frequently exposed to hares, rabbits or wild animals.
In Germany, there is an obligation to notify the authorities when F. tularensis ssp. is detected in hares and rabbits!