Tularemia (rabbit fever) is an infectious disease caused by Francisella (F.)tularensis. These are Gram-negative, pleomorphic, nonmotile, aerobic growing bacteria. They do not form spores, but are very robust to external conditions. There are four subspecies that can be distinguished: F. tularensis ssp. tularensis (biovar type A), ssp. holarctica (biovar type B), ssp. mediaasiatica and novicida.
Affected are mostly rodents, but also a variety of other animals of different susceptibility including birds. In an acute illness several symptoms such as apathy, fever, tachypnea and fur bristling can be observed. Depending on the infectious dose and susceptibility most animals die of septicemia within 2 to 13 days. In chronic cases severe emaciation, exhaustion, ulcerated skin lesions, and swelling of the lymph nodes occur. After 2 to 6 weeks a lethal outcome is possible.
Francisella tularensis ssp. tularensis and holarctica are clinically important and it is noteworthy that the type A strains have increased virulence. For this reason, these strains are to be processed in laboratory measures of safety level 3, while for all other subspecies the work can be done in the laboratory measures of safety level 2.
The course of this zoonosis in humans depends on the pathogen subtype, its virulence, the infectious dose and the mode of transmission in particular the portal of entry. F. tularensis ssp. tularensis occurs naturally in North America and is responsible for much more aggressive disease progression than F. tularensis ssp. holarctica which is occurring in the northern hemisphere.
Modes of transmission to humans are: skin - and mucous membrane contact with infectious animal material, consumption of improperly cooked, contaminated meat (rabbit) or water, bites from infected ticks or blood-sucking insects, contaminated dust and aerosols.
Acute tularemia can cause the following symptoms: fever, swollen lymph nodes, diarrhea, vomiting, respiratory distress and septic syndrome. The bacterium can be cultured from and detected in tissues from animals and man by molecular methods (eg PCR).
The detection of specific antibodies against F. tularensis is also possible serologically.
Disease and detection of the pathogen of tularemia are notifiable in hares and rabbits (amended ordinance on notifiable animal diseases 20 December 2005). The Notice of national reference laboratories for notifiable diseases and notifiable animal diseases, 5 December 2008, the location of FLI Jena has been appointed as the seat of the NRL for tularemia (Bundesanzeiger No. 196, 4701-4703).