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Tularemia

Tularemia (also known as "rabbit fever") is an infectious disease caused by the bacterium Francisella tularensis. The disease is endemic in North America, and parts of Europe and Asia. The primary vectors are ticks and deer flies, but the disease can also be spread through other arthropods. Rodents, rabbits, hares and ticks often serve as reservoir hosts. The disease is named after Tulare County, California. more...

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Mechanism of infection

Francisella tularensis is one of the most infective bacteria known. Fewer than ten organisms have been shown to lead to severe illness. Humans are most often infected by tick bite or through handling an infected animal. Ingesting infected water, soil, or food can also cause infection. Tularemia can be acquired by inhalation; hunters are at a higher risk for this disease because of the potential of inhaling the bacteria during the skinning process. Tularemia is not spread directly from person to person.

Francisella tularensis is an intracellular bacterium, meaning that it is able to live as a parasite within host cells. It primarily infects macrophages, a type of white blood cell. It is thus able to evade the immune system. The course of disease involves spread of the organism to multiple organ systems, including the lungs, liver, spleen, and lymphatic system. The course of disease is similar regardless of the route of exposure. Mortality in untreated patients can be as high as 30%, but the disease responds well to antibiotics. The exact cause of death is unclear, but it is thought be a combination of multiple organ system failures.

Incubation period

A patient with tularemia will most often develop flu-like symptoms between 1-14 days after infection (most likely 3-5 days.) If the patient was infected through an insect or tick bite, an eschar may develop at the bite site.

Treatment

The drug of choice is Streptomycin. Tularemia can also be treated with gentamicin, tetracycline or fluoroquinolone antibiotics.

Tularemia has been identified as a potential bioweapon by the Centers for Disease Control and Prevention (CDC). Because of its ability to be aerosolized and the extremely small number of bacteria needed to cause infection, it could be used against a dense urban population.

No vaccine is currently available to the general public. The best way to prevent tularemia infection is to wear rubber gloves when handling or skinning rodents (especially rabbits), avoid ingesting uncooked wild game and untreated water sources, and wearing long-sleeved clothes and using a insect repellant to prevent tick bites.

In summer 2000, an outbreak of tularemia in Martha's Vineyard resulted in one fatality, and brought the interest of the CDC as a potential investigative ground for aerosolized Francisella tularensis. Over the following summers, Martha's Vineyard was identified as the only place in the world where documented cases of tularemia resulted from lawn mowing. The research may prove valuable in preventing bioterrorism.

In 2004, three researchers at Boston University Medical Center were accidentally infected with tularemia, after apparently failing to follow safety procedures.

Read more at Wikipedia.org


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Tularemia
From Gale Encyclopedia of Medicine, 4/6/01 by Rosalyn S. Carson-DeWitt

Definition

Tularemia is an illness caused by a bacteria. It results in fever, rash, and greatly enlarged lymph nodes.

Description

Tularemia infects a variety of wild animals, including rabbits, deer, squirrels, muskrat, and beaver. Humans can acquire the bacteria directly from contact with the blood or body fluids of these animals, from the bite of a tick or fly which has previously fed on the blood of an infected animal, or from contaminated food or water.

Tularemia occurs most often in the summer months. It is most likely to infect people who come into contact with infected animals, including hunter, furriers, butchers, laboratory workers, game wardens, and veterinarians. In the United States, the vast majority of cases of tularemia occur in the southeastern and Rocky Mountain states.

Causes & symptoms

Five types of illness may occur, depending on where/how the bacteria enter the body:

  • Ulceroglandular/Glandular tularemia. 75-85% of all cases are of this type. This type is contracted through the bite of an infected tick that has defecated bacteria-laden feces in the area of the bite wound. A tender red bump appears in the area of the original wound. Over a few weeks, the bump develops a punched-out center (ulcer). Nearby lymph nodes grow hugely swollen and very tender. The lymph nodes may drain a thick, pus-like material. Other symptoms include fever, chills, and weakness. In adults, the lymph nodes in the groin are most commonly affected; in children, the lymph nodes in the neck.
  • Oculoglandular tularemia. This type accounts for only about 1% of all cases of tularemia. It occurs when a person's contaminated hand rubs his or her eye. The lining of the eyelids and the surface of the white of the eye (conjunctiva) becomes red and severely painful, with multiple small yellow bumps and pitted sores (ulcers). Lymph nodes around the ears, under the jaw, or in the neck may swell and become painful.
  • Oropharyngeal and Gastrointestinal tularemia. This type occurs when contaminated meat is undercooked and then eaten, or when water from a contaminated source is drunk. Poor hygiene after skinning and cleaning an animal obtained through hunting can also lead to the bacteria entering through the mouth. Sores in the mouth and throat, as well as abdominal pain, nausea and vomiting, ulcers in the intestine, intestinal bleeding, and diarrhea may all occur.
  • Pulmonary tularemia. This rare type of tularemia occurs when a person inhales a spray of infected fluid, or when the bacteria reach the lungs through the blood circulation. A severe pneumonia follows.
  • Typhoidal tularemia. This type of tularemia is particularly hard to diagnose, because it occurs without the usual skin manifestations or swelling of lymph glands. Symptoms include continuously high fever, terrible headache, and confusion. The illness may result in a severely low blood pressure, with signs of poor blood flow to the major organs (shock).

Diagnosis

Samples from the skin lesions can be prepared with special stains, to allow identification of the causative bacteria under the microscope. Other tests are available to demonstrate the presence of antibodies (special immune cells which the body produces in response to the presence of specific foreign invaders) which would be increasing over time in an infection with tularemia.

Treatment

Streptomycin (given as a shot in a muscle) and gentamicin (given as either a shot in a muscle or through a needle in the vein) are both used to treat tularemia. Other types of antibiotics have been tested, but have often resulted in relatively high rates of relapse (20%).

Prognosis

With treatment, death rates from tularemia are under 1%. Without treatment, however, the death rate may reach 30%. The pneumonia and typhoidal types have the worst prognosis without treatment.

Prevention

Prevention involves avoiding areas known to harbor ticks and flies, or the appropriate use of insect repellents. Hunters should wear gloves when skinning animals or preparing meat. Others (butchers, game wardens, veterinarians) who work with animals or carcasses should always wear gloves. A vaccine exists, but is usually only given to people at very high risk due to their profession or hobby (veterinarians, laboratory workers, butchers, hunters, game wardens).

Key Terms

Conjunctiva
The lining of the eyelids and the surface of the white part of the eye.
Shock
A state in which drastically low blood pressure prevents adequate blood flow to the tissues and organs throughout the body.

Further Reading

For Your Information

    Books

  • Jacobs, Richard F. "Tularemia." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1998.
  • Ryan, Kenneth J. "Some Bacteria Causing Zoonotic Diseases." In Sherris Medical Microbiology: An Introduction to Infectious Diseases, edited by Kenneth J. Ryan. Norwalk, CT: Appleton and Lange, 1994.

    Periodicals

  • Fredericks, David N. and Jack S. Remington. "Tularemia Presenting as Community-Acquired Pneumonia." Archives of Internal Medicine, 56 (18)(October 14, 1996): 2137+.
  • Schofield, Hal. "Infectious Disease: Leporidae's Revenge." Patient Care, 30 (14)(September 15, 1996): 171+.

    Organizations

  • Centers for Disease Control and Prevention. (404)332-4559. http://www.cdc.gov.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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