Tularemia

by National Institute of Health

Tularemia (also known as deerfly fever or rabbit fever) is an infectious disease caused by the bacterium Francisella tularensis. It is found naturally in small mammals such as rabbits, rodents, and hares, as well as the insects that feed on these animals. The bacteria can survive for weeks at low temperatures in water, moist soil, hay, straw, or decaying animal carcasses. Tularemia was first described by scientists in 1911. Its ability to infect whole populations was seen during outbreaks of waterborne disease in Europe and the Soviet Union in the 1930s and 1940s.

The Microbe

F. tularensis has two subspecies. Type A is common in North America and may be highly virulent in humans and animals. Type B probably causes all human tularemia in Europe and Asia.

How Common Is Tularemia?

Health experts believe that tularemia is underrecognized and underreported. There are approximately 200 reported cases in the United States each year; of these cases, less than two percent are fatal. Most cases occur in rural areas in the south -central and western states from June through September (tick season) and generally infect hunters. From 1995 to 1997, approximately half of all U.S. tularemia cases were reported from Missouri, Oklahoma, Kansas, and Arkansas. Worldwide, the disease occurs in eastern Europe, China, Japan, and Scandinavia, and almost always in rural areas.

Transmission

The most common ways people contract tularemia are by being bitten by flies, ticks, or other insects carrying the disease, handling infected animal tissue or fluids, eating or drinking food or water contaminated by the bacteria, breathing in the bacteria.

You can also get tularemia by having direct contact with or ingesting bacteria-contaminated water, food, or soil, handling contaminated animal skins, inhaling infective aerosols from materials containing the bacteria.

In Europe, there have been cases where the disease was caused by inhaling airborne bacteria generated during farm work, such as transporting infected hay. A small number (about 10 to 50 organisms) can cause disease.

If the bacteria were to be used as a weapon, they would likely be made airborne for human exposure by inhaling them. Making an effective aerosol weapon using F. tularensis , however, would require considerable sophistication.

Laboratory workers also can become infected by inhaling bacteria while examining an open culture plate, for example.

There is no evidence you can get the disease from another person.

Symptoms

Tularemia infection varies from a mild illness to acute sepsis (serious infection of the blood or other tissues) and rapid death. After exposure to the bacteria, you will usually develop symptoms within 3 to 5 days, but they can take up to 21 days to appear. Symptoms include

• Sudden fever
• Chills
• Headaches
• Diarrhea
• Muscle aches
• Joint stiffness or pain
• Dry cough
• Weakness

In most people, progressive weakness leads to a dry cough and pneumonia. Tularemia-induced pneumonia can cause chest pain, bloody sputum (phlegm), and trouble breathing. Depending on how you were exposed to the bacteria, other symptoms may include

• A red spot on the skin that enlarges to an ulcer
• Ulcers in the mouth
• Swollen and painful lymph glands
• Swollen and painful eyes
• Sore throat

The inhalation form of tularemia begins 3 to 5 days after you have been exposed to the bacteria. In some cases, pneumonia develops after several days or weeks. If left untreated, the disease could lead to respiratory failure.

Diagnosis

Health care providers can diagnosis tularemia by blood or sputum laboratory tests.

Treatment

If you think you have symptoms of tularemia, contact your health care provider as soon as possible. Antibiotics, such as doxycycline or ciprofloxacin, can effectively treat tularemia. A tularemia vaccine strain is being reviewed by the Food and Drug Administration, but its future availability is uncertain, mainly because of the length of time it takes for the vaccine to work (about 2 weeks).

The U.S. Department of Defense also has developed an experimental tularemia vaccine. To date, health officials have limited the use of this vaccine to laboratory and other high-risk workers.

Prevention

To prevent insect bites use insect repellent containing the ingredient DEET on your skin, treat your clothing with insect repellant containing permethrin.

Other ways to prevent tularemia include

• Washing your hands often with soap and warm water, especially after handling animal carcasses
• Cooking your food thoroughly
• Drinking water that is from a safe source

Research

The National Institute of Allergy and Infectious Diseases (NIAID) supports research on the diagnosis, prevention, and treatment of infections caused by microbes, including those that have the potential for use as biological weapons. The research program to address biodefense includes both short- and long-term studies targeted at designing, developing, evaluating, and approving specific tools (diagnostics, therapies, and vaccines) needed to defend against possible bioterrorist-caused disease outbreaks.

NIAID research goals to diagnose, prevent, and treat tularemia include

• Supporting basic research to identify mechanisms of F. tularensis virulence and pathogenesis, and to define host responses to pathogen
• Developing quick and inexpensive ways to diagnose tularemia
• Developing antimicrobials and immunotherapies with novel mechanisms of action to treat tularemia
• Identifying new F. tularensis vaccine candidates that can prevent or modulate infection both before and after exposure
• Conducting clinical trials of vaccine candidates

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.