Article: Tularemia

Overview

Tularemia (also known as deerfly fever or rabbit fever) is an infectious disease caused by the bacterium Francisella tularensis. It is naturally found 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, and its ability to infect whole populations was seen during outbreaks of waterborne disease in Europe and the Soviet Union in the 1930s and 1940s.

There are about 200 reported cases of human tularemia in the United States every year. Most occur in rural areas in the south-central and western states. Of these cases, less than 2 percent are fatal.

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.

Transmission

The most common ways people contract tularemia are

  • Being bitten by flies or ticks carrying the disease
  • Handling infected animal tissue or fluids
  • Eating insufficiently cooked rabbit meat in which the bacteria were not destroyed by cooking

Tularemia also can be spread by

  • Having direct contact with or ingesting bacteria-contaminated water, food, or soil
  • Handling contaminated animal skins
  • Inhaling infective aerosols

In Europe, there have been cases of the disease caused by inhaling airborne bacteria generated during farm work, such as moving infected hay. Laboratory workers also can become infected by inhaling bacteria while examining an open culture plate, for example.

There are no documented cases of human-to-human transmission.

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, a person will usually develop symptoms within 3 to 5 days, but they can take up to 21 days to appear. Symptoms include

  • Sudden, abrupt onset of fever
  • Chills
  • Headaches
  • Muscle aches
  • Joint stiffness or pain
  • Weakness

In most patients, progressive weakness leads to a dry cough and pneumonia. Tularemia-induced pneumonia can cause chest pain, bloody sputum, and trouble breathing. Depending on how a person was 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 exposure. In some cases, pneumonia develops after several days or weeks. If left untreated, the disease could lead to respiratory failure.

Diagnosis

Health care workers can diagnosis tularemia by doing laboratory tests on blood or sputum.

Treatment

Antibiotics, such as doxycycline or ciprofloxacin, can effectively treat people with tularemia. A tularemia vaccine strain is being reviewed by the U.S. 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.

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. Most cases occur in rural areas 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 Eurasia-most commonly in northern and central Europe-and almost always in rural areas.

Research

The National Institute of Allergy and Infectious Diseases (NIAID) is part of the National Institutes of Health, an agency of the U.S. Department of Health and Human Services. 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.

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

  • 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

More Information

National Institute of Allergy and Infectious Diseases
31 Center Drive, MSC 2520
Bethesda, MD 20892-2520
http://www.niaid.nih.gov

National Library of Medicine
MEDLINEplus
8600 Rockville Pike
Bethesda, MD 20894
1-800-338-7657
http://www.nlm.nih.gov/medlineplus

U.S. Centers for Disease Control and Prevention
1600 Clifton Road
Atlanta, GA 30333
1-888-232-3228
http://www.bt.cdc.gov/

Johns Hopkins University Center for Civilian Biodefense Studies
http://www.hopkins-biodefense.org/pages/agents/agenttularemia.html


Source: National Institute of Allergy and Infectious Diseases
Cache Date: December 10, 2004

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