Tularemia


Tularemia

Description, Causes and Risk Factors:

Tularemia is a bacterial zoonotic disease of the northern hemisphere. The bacterium (Francisella tularensis) is highly virulent for humans and a range of animals such as rodents, hares and rabbits. It may cause epidemics and epizootics. F. tularensis is transmitted to humans (i) by arthropod bites, (ii) by direct contact with infected animals, infectious animal tissues or fluids, (iii) by ingestion of contaminated water or food, or (iv) by inhalation of infective aerosols. There is no human-to-human transmission.

Tularamia is reported from most countries in the northern hemisphere, although its occurrence varies widely from one region to another. In some countries, endemic regions with frequent outbreaks are close to regions that are completely free of tularemia. There is also a wide variation with time. In an endemic area, tularemia may occur annually within a 5-year period, but may also be absent for more than a decade. The reasons for this temporal variation in the occurrence of outbreaks are not well understood. When, after a long lapse, the first case of a new outbreak appears, the disease may be more or less forgotten and is therefore not easily diagnosed.

F. tularensis subspecies tularensis (type A) is one of the most infectious pathogens known in human medicine. The infective dose in humans is extremely low: 10 bacteria when injected subcutaneously and 25 when given as an aerosol. For example, on Martha's Vineyard in the United States of America, two adolescents contracted respiratory tularaemia after mowing a grassed area. It is believed that an aerosol of F. tularensis subspecies tularensis was generated after the carcass of a rabbit which had died of tularemia was accidentally shredded by the lawnmower.

Causes:

    Contaminated food or water. Although uncommon, it's possible to get tularemia from eating 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 (71 C) — is usually safe to eat.

  • 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.

  • 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.

Risk Factors:

  • Gardening or landscaping. Gardeners and landscapers may also be at risk of tularemia. They are more likely to develop pneumonic tularemia, one of the least common and most deadly forms of the disease. It's possible that gardeners inhale bacteria that are stirred up while working the soil or when using mowers and weed trimmers.

  • Hunting and trapping. Because hunters handle wild animals, are exposed to animal blood and may eat the meat, they're at risk of tularemia.

  • Wildlife management and veterinary medicine. People who work with wildlife are at increased risk of tularemia.

The risk posed by tularemia can be properly managed, provided the public health system is well prepared. In order to avoid laboratory-associated infection, safety measures are needed and consequently clinical laboratories do not generally accept specimens for culture. However, since clinical management of cases depends on early recognition, there is an urgent need for diagnostic services. In addition to its natural occurrence, F. tularensis causes great concern as a potential bioterrorism agent.

Symptoms:

Symptoms of tularemia depend on the virulence of thebacterial strain and route of infection. Symptoms of all formsof tularemia typically include fever, headache, body aches,and malaise. Symptoms usually develop within 3 to 5 daysof infection; however, the incubation period can be 1 to 14days. Naturally occurring tularemia infection can take severalforms. Pneumonic tularemia (theform expected from an aerosol release) is likely to cause typicalsymptoms of pneumonia (eg, fever, cough, and shortnessof breath).

Diagnosis:

Because it's rare and because it shares symptoms with other diseases, tularemia may be difficult to diagnose. Doctors may check for F. tularensis in a blood or sputum sample that's cultured to encourage the growth of the bacteria. But the preferred way to diagnose tularemia usually is to identify antibodies to the bacteria in a sample of blood. You're also likely to have a chest X-ray to look for signs of pneumonia.

More rapid diagnosis may be obtained through use a polymerase chain reaction (PCR) test, although this may be falsely negative in up to one-third of cases. Other rapid tests under study include special fluorescent stains, tests that detect parts of the bacteria in the urine, and experimental tests for bacterial RNA. Infected patients make antibodies against F. tularensis and these antibodies may be detected in the blood after the first week of illness. High titers of antibodies indicate a high likelihood of disease. However, antibodies may simply represent disease that happened in the remote past rather than an acute illness.

Treatment:

The drug of choice is streptomycin. Tularemia may also be treated with gentamicin for ten days, tetracycline-class drugs such as doxycycline for two to three weeks, chloramphenicol, or fluoroquinolones. An attenuated, live vaccine is available, but its use is only for high risk groups. Its use as postexposure prophylaxis is not recommended.

Several precautions can protect individuals from tularemia.

    Avoid drinking, bathing, swimming or working in untreated water where infection may be common among wild animals.

  • Use impervious gloves when skinning or handling animals, especially rabbits.

  • Cook the meat of wild rabbits and rodents thoroughly.

  • Avoid being bitten by deer flies and ticks. The following suggestions may help:

  • Check your clothing often for ticks climbing toward open skin. Wear white or light-colored long-sleeved shirts and long pants so the tiny ticks are easier to see. Tuck long pants into your socks and boots. Wear a head covering or hat for added protection.

  • For those who may not tolerate wearing all of these clothes in hot, muggy weather, apply insect repellent containing DEET (30 percent or less) to exposed skin (except the face). Be sure to wash treated skin after coming indoors. If you do cover up, use repellents containing permethrin to treat clothes (especially pants, socks and shoes) while in locations where ticks may be common. Follow label directions; do not misuse or overuse repellents. Always supervise children in the use of repellents.

  • Walk in the center of trails so weeds do not brush against you.

  • Check yourself, children and other family members every two to three hours for ticks. Most ticks seldom attach quickly and rarely transmit tickborne disease until they have been attached for four or more hours.

  • If you let your pets outdoors, check them often for ticks. Infected ticks also can transmit some tickborne diseases to them. (Check with your veterinarian about preventive measures against tickborne diseases.) You are at risk from ticks that "hitch a ride" on your pets but fall off in your home before they feed.

  • Make sure the property around your home is unattractive to ticks. Keep your grass mowed and keep weeds cut.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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