Tularemia is a bacterial disease that affects people and many species of wild and domestic animals. It is caused by toxins in the blood produced by the bacterium Francisella tularensis. The bacteria can survive for weeks or months in a moist environment. There are 3 types of organisms that differ based on the severity of the disease they produce. Type A is most likely to cause rapid and severe disease. It is found most commonly in North America. Disease resulting from Type B infection is generally mild and occurs most commonly as a result of contact with arthropods (ticks, fleas, or flies) that spread the disease or ingestion of contaminated water in North America and Eurasia. Type C is the least common and least severe type of tularemia.
In domestic animals, sheep are infected most frequently, but infection has been reported in dogs, cats, pigs, and horses. It is possible that many mild cases go untreated and unreported among pets and livestock. Infection occurs most commonly in cottontail and jackrabbits, beaver, muskrat, meadow voles, and sheep in North America, and other voles, field mice, and lemmings in Europe and Asia. Although found in every state except Hawaii, tularemia is most often reported in the south central and western US (California, Missouri, Oklahoma, South Dakota, and Montana). Dogs appear to be relatively resistant to the bacteria, and infections in dogs are rare.
The disease can be transmitted from animals to people by several routes. The most common mode of transmission to people is from the bite of an infected tick. Direct transmission can occur from contact with moist tissue when skinning and preparing wild game. Inhalation of organisms in the air can cause disease in the lungs. Other sources of infection include eating infected, undercooked game and drinking contaminated water. Rarely, the bite of a cat that has recently fed on an infected animal has been found to be a source of human infection.
Dogs can become infected with tularemia in the same ways that people do. In addition, dogs can become infected by eating dead animals.
In most mammals, signs of illness may include tick infestation, swollen glands, the sudden onset of high fever, lethargy, and poor appetite. Other signs may include stiffness and reduced mobility and are associated with a generalized infection. Pulse and respiratory rates may also be increased, and the infected animal may have a cough, diarrhea, and frequent urination. Prostration and death may occur in a few hours or days. Very mild cases without signs may be common.
Veterinarians treat cases of tularemia with an antibiotic. Early treatment should prevent death; however, prolonged treatment may be necessary. Control is difficult and is limited to reducing tick infestation and to rapid diagnosis and treatment. Animals that recover develop a long-lasting immunity.
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