What is tularemia?
Tularemia is a rare and highly infectious disease caused by Francisella tularensis bacteria. It is also called rabbit fever or deer fly fever. The bacteria can infect a wide range of animals, including rabbits and hares, beavers, muskrats, squirrels, and mice, and transmit the disease to people. Cases of tularemia have occurred in household pets, such as dogs, cats, and hamsters.
How common is tularemia?
There are few reported cases of tularemia in the United States (about 100 to 200 cases reported per year), and it is considered a rare disease. However, some cases may be misdiagnosed or go unreported because the symptoms of the disease resemble those of other illnesses. A majority of the confirmed cases have occurred in rural parts of Arkansas, Kansas, Missouri, and Oklahoma. People of all ages can become infected, although males are at higher risk than females.
Symptoms and Causes
What causes tularemia?
Bites from ticks, flies, mosquitoes or other insects that carry the Francisella tularensis bacteria can infect humans and animals. Wild animals frequently die after being infected, but people who receive prompt treatment can recover from tularemia. A person infected with tularemia cannot pass the infection along to another person. However, F. tularensis bacteria are very infectious and can survive for long periods in the environment. The main ways that tularemia can be transmitted to humans include:
- Being bitten by ticks, horse flies, deerflies, or mosquitoes
- Handling live or dead animals infected with tularemia or their fluids or tissues
- Eating food or drinking water that is contaminated
- Inhaling a fine mist or spray (aerosol) or dust particles containing the bacteria
People who work outdoors or pursue outdoor activities such as hunting, trapping, hiking, or camping are at greater risk of contracting tularemia. Laboratory workers who handle biological samples from infected animals or humans can also be at risk unless they take proper safety measures.
What are the symptoms of tularemia?
Symptoms may vary widely, depending on the route of transmission. They can range from mild to severe. In some cases, there are no symptoms, or signs of infection are not noticed. The infection can be life threatening, if untreated. Usually, it takes from three to five days after infection before symptoms appear, but it might take up to two to three weeks.
Symptoms of tularemia may include:
- Skin ulcer or rash
- Swollen or tender lymph nodes
- Sudden fever
- Muscle pain
- Joint pain
- Malaise (a general feeling of being ill)
The way that the bacteria enters the body may affect symptoms. They may persist for several weeks. There are several major forms of tularemia, based on the route of transmission.
- Ulceroglandular: This is the most common type of the infection, usually transmitted by a tick or deer fly bite or by handling an infected animal. A skin ulcer or rash often appears at the area where the bacteria enter the body, and the lymph glands may become swollen or tender.
- Glandular: This form is similar to the ulceroglandular form, except there is no skin ulcer. It also is transmitted by insect bites or infected animals.
- Oropharyngeal: Tularemia may enter the body through the mouth if you eat contaminated or undercooked meat or drink contaminated water. You may develop symptoms such as a sore throat, mouth sores, or stomach pain. Nausea, vomiting, or diarrhea may occur.
- Oculoglandular: Tularemia bacteria can enter the eye through contact with bacteria on the fingers or hands. Hunters who skin and dress meat from rabbits or other animals may be prone to eye infections. Inflammation of the membrane of the eye (conjunctivitis) may cause eye pain, redness, and itching. Swollen lymph glands also may occur.
- Pneumonic: This is a very serious form of tularemia and may be life-threatening. It affects the lungs. It occurs when people inhale dust or fine droplets containing the bacteria. Symptoms may include coughing, chest pain, and breathing problems. Fluid may build up around the lung, or lung abscesses may occur.
- Typhoidal: This type is a general form of tularemia whose symptoms include fever, joint pain, and malaise. It may be hard to find out how the infection entered the body. This type affects the bloodstream and major organs. Symptoms can include diarrhea, enlargement of the spleen and liver, and jaundice.
Diagnosis and Tests
How is tularemia diagnosed?
It may be difficult to diagnose tularemia because its symptoms may look like those of other infections. Your doctor will conduct a physical exam and ask questions about your medical history. You should tell your doctor about any possible exposure to infected animals or insect bites.
If your doctor suspects tularemia, he or she may order laboratory tests to confirm the diagnosis. There are no rapid lab tests for tularemia.
Laboratory tests may include:
- Blood tests
- Bacterial cultures: Bacteria may be grown on culture media in the laboratory to confirm a suspected case. Biological samples, such as scrapings or swabs taken from skin lesions, sputum, tissue obtained from a biopsy, or throat swabs, may be collected.
Management and Treatment
How is tularemia treated?
Antibiotics may be administered over a period of ten days to three weeks. Some antibiotics that are effective against tularemia are:
- Aminoglycosides (streptomycin, gentamicin): Streptomycin is the drug of choice. It is injected into a muscle (intramuscular). Gentamicin may be given as an intravenous (IV) fluid. However, aminoglycosides can cause severe side effects and may not be suitable for all patients.
- Quinolones (ciprofloxacin)
- Tetracyclines (doxycycline)
How can tularemia be prevented?
There is no way to prevent an infection completely. No vaccine against tularemia is available to the general public. Laboratory workers at higher risk of infection have to take special preventive measures against the disease. However, the risk of infection can be reduced by following these precautions when working or spending time outdoors.
- Use insect repellants containing picaridin, DEET, or IR3535.
- Avoid insect bites by wearing long pants, long sleeves, and socks to cover skin.
- Avoid drinking untreated surface water that might be contaminated.
- Check lawns or grassy areas for sick or dead animals before mowing the lawn.
- Wear gloves when handling animal carcasses, especially those of rodents and rabbits.
- Cook meat from game animals thoroughly before eating it.
Outlook / Prognosis
What are the complications of tularemia?
The outlook depends on the route of transmission and how soon treatment is started. There may be occasional relapses, but those who recover develop immunity to the bacteria. You should take antibiotics as ordered to prevent a relapse.
The highest mortality rates are associated with the pneumonic and typhoidal forms of tularemia, if left untreated.
In severe cases, tularemia can be fatal or lead to serious complications, such as: