Tularemia, also known as rabbit fever, is caused by the bacteria Francisella tularensis. The disease is found throughout the United States and has been reported in every state except Hawaii. F. tularensis can survive in water, soil and decaying carcasses for up to six months. Tularemia is uncommon, but is a potentially fatal disease for cats, humans and most other animals.

Cats become infected either by ingesting infected prey (rabbits or rodents) or by being bitten by an infected tick. Cats can transmit the disease to humans through bites and scratches or by human exposure to infected cat tissue. Cats do not have to be clinically ill to transmit the disease to humans. Humans most commonly become infected through tick and insect bites, contaminated soil or water, aerosolization or contact with other infected animals.

Ticks serve as hosts for the disease and vectors that transmit the organism to humans and other mammals. Rodents and lagomorphs (rabbits) also serve as sources of infection for humans and cats.

There are a variety of clinical forms of the disease. The type of disease is related to the route of transmission and the virulence of the strain of bacteria. After an incubation period of 3-5 days (up to 14 days) mild to severe clinical signs may appear. F. tularensis enters cells and multiplies in macrophages before disseminating through the blood stream to internal organs where it can cause abscesses and even death. Clinical signs in cats can vary from very mild febrile illness to severe infection and death. The most common signs seen in severely infected cats are: marked depression, enlarged lymph nodes, oral ulcers, panleukopenia and hyperbilirubinemia. Humans commonly experience fever, headache, muscle pain, enlarged lymph nodes and malaise. People who experience these signs should consult their physician. In the United States the fatality rate for humans is less than two percent.

Diagnosing tularemia can be complicated. It stains poorly and is generally not seen with standard stains. Culture requires special media and handling. The most common method of diagnosis is by detection of antibodies to the bacteria. However, infection can be present for 2-3 weeks before detectable levels of antibody are present in the blood. A presumptive diagnosis of tularemia is made when there is a four-fold increase in antibody titer from blood samples collected 2-4 weeks apart. A more rapid method of diagnosis is with direct or indirect fluorescent antibody tests. These tests may be done on bone marrow samples or lymph nodes aspirates collected before treatment is initiated. Tularemia can be successfully treated with appropriate antibiotics.

The best methods to prevent tularemia in animals are to control ticks and confine your pet. Hunters should wear gloves when preparing game and use tick repellent and protective clothing when entering tick infested areas. Awareness of the disease and appropriate preventive measures have caused the number of cases diagnosed in the US to decline dramatically over the last century.

Recently, Francisella tularensis has been classified as a Category A bioterrorism agent and all confirmed cases should be reported to the appropriate local or state health officials.