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Causes
By Mayo Clinic staffTularemia doesn't occur naturally in humans, but it does in animals. Worldwide, more than 200 species of mammals, as well as birds, insects and fish, may be infected with F. tularensis. The bacteria can live for an extended time in animals, and even insects can act as reservoirs for disease. Unlike some infectious diseases that spread from animals to people through a single route, tularemia has several modes of transmission. How you get the disease usually determines the type and severity of symptoms. In general, you can get tularemia through:
- Insect bites. Although a number of insects carry tularemia, ticks and deerflies are most likely to transmit the disease to humans. Tick bites cause a large number of cases of ulceroglandular tularemia.
- Exposure to sick or dead animals. Ulceroglandular tularemia can also result from handling or being bitten by an infected animal, most often a rabbit or hare. Bacteria enter the skin through small cuts and abrasions or a bite, and an ulcer forms at the wound site. The ocular form of tularemia can occur when you rub your eyes after touching an infected animal.
- Airborne bacteria. Bacteria in the soil can become airborne during gardening, construction or other activities that disturb the earth. Inhaling the bacteria can lead to pneumonic tularemia. Laboratory workers who work with tularemia also are at risk of airborne infection.
- Contaminated food or water. Although uncommon, it's possible to get tularemia from eating the undercooked meat of an infected animal or drinking contaminated water. The signs include vomiting, diarrhea and other digestive problems (oropharyngeal tularemia). Heat kills F. tularensis, so well-cooked meat — at least 160 F (71C) — is usually safe to eat.
Tularemia: Where, when and how much
- Where. Tularemia occurs worldwide — especially in rural areas in eastern Europe, China and Japan. In the United States, most cases are clustered in the rural western and in south-central states, such as Arkansas, Missouri and Oklahoma.
- When. Tick season (generally June through September) and hunting season are prime times for infection.
- How much. Tularemia is highly contagious. Inhaling as few as 10 to 50 bacteria can cause disease. Yet tularemia is rare, with only about 200 cases reported each year. The bacteria are transmitted from animals to humans, not from person to person.
