What is tularemia?
Tularemia is an infection caused by the Gram-negative bacteria Francisella tularensis. The organism is named after Edward Francis who, while in Tulare County, California, helped discover how the disease was spread and how the causative organism could be cultured.
Tularemia is usually a disease of animals. Humans can acquire tularemia when they come in contact with infected animals or are bitten by insects that have fed on an infected animal. Ticks, biting flies, and mosquitoes have been shown to transmit tularemia between animals and humans. Tularemia is one of several tick-borne diseases and can be spread by many species of ticks, including Dermacentor variabilis and Amblyomma americana. Among biting flies, the deer fly (Chrysops spp.) is the most widely cited insect that transmits the disease (vector). Even small doses of these bacteria (10-50 bacteria) have the potential to cause severe disease. For this reason, F. tularensis has the potential to be used as a bioweapon.
What are the different types of tularemia?
There are four subspecies of F. tularensis, and all are capable of causing disease in humans (F. tularensis, F. holarctica, F. mediasiatica, and F. novicida). The subspecies tularensis and holarctica are the most common causes of tularemia in humans. The type of tularemia depends on which subspecies is involved and how the organism was acquired. Disease caused by the subspecies F. holarctica is often milder than that caused by F. tularensis.
The type of disease is often named for the most prominent symptoms. Thus, ulceroglandular tularemia is usually caused by inoculation of the skin and is associated with open sores and swollen lymph nodes. If there is no sore but swollen lymph nodes are prominent, the disease may be classified as glandular. If the eye or throat is involved, oculoglandular or pharyngeal tularemia is said to be present. Disease involving the lungs is termed pneumonic disease. Tularemia that predominately affects the bloodstream and body organs is referred to as typhoidal tularemia. Some researchers classify tularemia into two groups: ulceroglandular and typhoidal. However, others classify seven different types according to where they occur:
- Ulceroglandular: cutaneous ulcers
- Glandular: regional adenopathy
- Oculoglandular: conjunctivitis
- Oropharyngeal: mouth and oral cavity
- Intestinal: abdominal organs
- Pneumonic: lungs
- Typhoidal: general feverish (febrile) illness
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Tularemia Symptoms & Signs
Swollen Lymph Nodes
Swollen lymph glands are typically a result of local or widespread inflammation, but sometimes enlarged lymph nodes are due to cancer.
Symptoms of swollen lymph nodes include
- localized pain,
- warmth in the involved area.
What causes tularemia?
Tularemia is caused by the bacterium Francisella tularensis. Tularemia is an uncommon disease in humans, with statistics showing less than one case per million people per year in the U.S. This translates into less than 150 cases per year, with a majority in Arkansas, Kansas, Missouri, and Oklahoma. Illness caused by ticks and insects is most common in the summer months and often occurs in children. Disease caused in winter is associated with hunters who handle dead animals. F. tularensis can infect many types of animals but particularly affects rabbits, hares, and rodents. The disease is sometimes called rabbit fever because it occurs when hunters contact the skin of infected rabbits. Farmers, veterinarians, foresters, landscape workers, and hunters are at risk of contracting tularemia because of their likely direct animal contact, but the disease can also affect others who inadvertently come into contact with animals or are bitten by insects.
Tularemia is usually acquired directly by skinning, eating, or otherwise handling infected animals. In rare instances, transmission has occurred when wild rodents (prairie dogs) were sold as pets. Dried animal material may be aerosolized and inhaled, causing disease. Domestic animals such as cats may pick up the organism on their claws after killing a wild rodent or rabbit. Dogs and cats may also eat contaminated meat, causing fever and swollen nodes. Transmission of tularemia from dogs or cats to humans is rare. Finally, the disease has been transmitted by drinking water contaminated with animal products. Contaminated food and water have been responsible for large outbreaks in times of war.
What are risk factors for tularemia?
Risk factors for tularemia include bites from almost any kind of animal (for example, domesticated dogs or cats can become infected, rodents, wild rabbits), tick bites, aerosols created from animal carcasses and/or bioweapons, handling animal carcasses (for example, skinning animals, sheering sheep), being a veterinarian, landscaper, hiker, or hunter, and eating or drinking contaminated foods.
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What are tularemia symptoms and signs?
Symptoms usually appear three to five days after the organism is acquired, although longer incubation periods (14 days) have been reported. Patients become ill suddenly and have influenza-like symptoms with fever, aches, and fatigue, and headache. A nonspecific rash may occur. Fever may be high, and may go away for a short time only to return. Untreated, the fever usually lasts about four weeks.
Other symptoms depend on the type of tularemia. In ulceroglandular tularemia, a red nodule appears at the site of inoculation and eventually forms an open sore associated with swollen lymph nodes. If untreated, the sore and the swollen lymph nodes resolve slowly over a period of months. Lymph nodes may become filled with pus (suppurate) and require drainage. In glandular tularemia, there is significant swelling of a group of lymph nodes but no detectable sore. The eye is infected (oculoglandular disease) when touched by contaminated hands, causing pain, swelling, and discharge. Oculoglandular disease is accompanied by swollen lymph nodes around the ear and neck.
Pharyngeal tularemia is usually acquired through eating or drinking and causes a sore throat. Necrotic tissue and pus often line the throat, and the lymph nodes of the neck are swollen.
Typhoidal tularemia causes infection of many organs and the bloodstream. Patients with typhoidal tularemia may experience diarrhea or jaundice. As the disease progresses, the liver and spleen may become enlarged. Pneumonia may occur at presentation or may be a late complication. In severe disease, the kidneys and other organs may fail.
Pneumonic tularemia is caused by inhalation of infected material or by spread of the organism to the lung from other sites. Inhalation may occur while farming, mowing a yard (mowing over dead rodents), or sheering sheep. Laboratory workers may become infected when material is inadvertently aerosolized in the lab. Pneumonia may occur in any of the types of tularemia but is especially common in typhoidal tularemia.
Is tularemia contagious, and what is the contagious period for tularemia?
Tularemia is not transmitted from person to person, so there is no contagious period for tularemia. However, some medical authors consider tularemia to be highly contagious to humans from environmental sources because of the small number of bacteria it takes to cause potentially lethal infections. Contagiousness from environmental sources can be long-lived, as the organisms can survive in cool, moist environments for weeks or months.
What is the incubation period for tularemia?
The incubation period for tularemia (the time it takes to develop signs and symptoms after exposure to the organisms) varies with the size of the inoculum; as few as 10 organisms may cause infection. The average incubation period is about two to six days but can range from one to 21 days.
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What types of specialists treat tularemia?
Specialists who help diagnose and treat tularemia are infectious-disease specialists, critical-care specialists, and pulmonologists. Other specialists may be consulted depending upon where the organisms spread inside the body. (For example, a cardiologist may be consulted if pericarditis develops.)
How do health-care professionals diagnose tularemia?
The first step in diagnosing tularemia is to suspect the disease. Because tularemia is rare, physicians may not think to ask about a history of tick bite or an occupational exposure such as hunting. Tissues or blood may be sent for culture, which requires special media. It is critical to warn the laboratory that tularemia is suspected because the organism poses a threat to laboratory workers. 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.
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What is the treatment for tularemia?
Tularemia is treated with a drug called streptomycin, an aminoglycoside antibiotic. The drug is given intramuscularly, twice a day, for one to two weeks. The antibiotic gentamicin is an alternative drug and may be given intravenously. Neither of these drugs is effective against meningitis because they do not penetrate from the bloodstream into the brain. In tularemic meningitis, it may be necessary to put gentamicin directly into the fluid that bathes the brain.
The oral medications doxycycline (Vibramycin) or tetracycline (Sumycin) may work but are less effective than streptomycin. The disease may relapse after treatment with these pills. Other drugs, such as ciprofloxacin (Cipro), are effective in the test tube but have not been widely used in patients. However, one outbreak in Spain with 142 patients showed good clinical outcomes with ciprofloxacin; fluoroquinolone antibiotics may be useful in treating tularemia if additional studies show clinical effectiveness.
Are there home remedies for tularemia?
There are no home remedies for tularemia. It is a relatively rare disease but can quickly become fatal (60% of individuals infected may die from it) if not treated with appropriate antimicrobials.
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Is there a vaccine for tularemia?
There is no vaccine for tularemia currently licensed in the U.S. An older vaccine made from a weakened strain of F. tularensis had many other problems and was withdrawn. There is great interest in developing a new vaccine, not only to protect those at high risk for disease (lab workers or researchers who routinely handle the bacteria), but also for counterterrorism to reduce the threat of biological warfare. The National Institutes of Health is funding several research projects to develop an effective vaccine against F. tularensis.
If a person is exposed to tularemia in a high-risk situation, such as in a laboratory accident, a two-week course of doxycycline or ciprofloxacin pills is recommended. Exposures from tick bites or other low-risk settings do not require preventive antibiotics.
To prevent and/or reduce the risk of tularemia, hunters should not handle wild animals with their bare hands. If a pet brings a killed rodent inside, the rodent should not be touched by the person who disposes of it. Tick bites can be avoided by wearing long pants and sleeves. Hikers should check themselves for ticks every day. If a tick is found on the body, it should not be removed with bare hands. Insect bites may be minimized by using insect repellents.
What is the prognosis for tularemia?
The prognosis for tularemia may range from good to poor, depending upon the type of tularemia and how quickly it is properly treated. Untreated tularemia is fatal in up to 60% of cases and is often due to organ failure. With treatment, deaths are rare and the mortality rate is less than 5%. However, many patients have fatigue that continues for months after the infection resolves. Less common complications of tularemia include meningitis, bone infection, or infection of the heart.
Tularemia and bioterrorism
F. tularensis can be freeze-dried and made into a powder which can be aerosolized. This makes it a potential source of bioterrorism similar to anthrax, botulism, or brucellosis because it could be delivered to large numbers of people. Once inhaled, it is estimated that more than 80% of people would become infected and 6% would die. Inhalation of only about 10-50 bacteria can cause disease. If the number of people exposed was large enough, infected people would overwhelm the health-care system and infected soldiers would be unable to fight. Tularemia is difficult to diagnosis, and few people are immune to the disease.
Where can people find more information about tularemia?
Centers for Disease Control and Prevention, "Tularemia"
United States Department of Labor, Occupational Safety & Health Administration
United States. Centers for Disease Control and Prevention. "Key Facts About Tularemia." Oct. 7, 2003. <http://www.bt.cdc.gov/agent/tularemia/facts.asp>.
United States. United States Department of Labor, Occupational Safety & Health Administration. "Tularemia." <http://www.osha.gov/SLTC/tularemia/index.html>.