Tularemia is an infection that can strike humans and animals. It is caused by the bacterium Francisella tularensis. The disease causes fever, localized skin or mucous membrane ulcerations, regional swelling of lymph glands, and occasionally pneumonia.
G.W. McCay discovered the disease in Tulare County, California, in 1911. The first confirmed case of human disease was reported in 1914. Edward Francis, who described transmission by deer flies via infected blood, coined the term tularemia in 1921. It has been considered an important biological warfare agent because it can infect many people if dispersed by the aerosol route.
Rabbits and ticks most commonly spread tularemia in North America. In other areas of the world, tularemia is transmitted by water rats and other aquatic animals.
The bacteria are usually introduced into the victim through breaks in the skin or through the mucous membranes of the eye, respiratory tract, or GI tract. Ten virulent organisms injected under the skin from a bite or 10-50 organisms breathed into the lungs can cause infection in humans. Hunters may contract this disease by trapping and skinning rabbits in some parts of the country.
Signs and symptoms
Tularemia can be divided into 2 forms: the ulceroglandular (75% of cases) and typhoidal (25% of cases). Victims with the ulceroglandular type have sores on the skin or mucous membranes, large lymph nodes, or both. Those with typhoidal tularemia have smaller lymph nodes and no skin sores.
After 3-6 days, people with the ulceroglandular form of the disease develop a group of symptoms: fever, chills, headache, cough, and muscle aches. They may also have chest pain, vomiting, joint pain, sore throat, abdominal pain, diarrhea, shortness of breath, back pain, or neck stiffness.
A sore up to an inch across may appear on the skin in about 60% of people and is the most common sign of tularemia. If the bite associated with infection was from an animal carrying the disease, the sore is usually on the upper part of a person’s body, such as on the arm. If the infection came from an insect bite, the sore might appear on the lower part of the body, such as on the leg.
Enlarged lymph nodes are seen in about 85% of victims and may be the initial or the only sign of infection. Although enlarged lymph nodes usually occur as single lesions, they may appear in groups. Enlarged lymph nodes may come and go and last for as long as 3 years. When swollen, they may be confused with buboes of bubonic plague.
Sore throat and other complications may occur in up to 25% of people with tularemia.
People with either type of tularemia may develop pneumonia. They may have a productive or nonproductive cough and possibly chest pain, shortness of breath, and vomit blood.
Tularemia can be diagnosed by growing the bacteria in the laboratory from samples taken of blood, ulcers, sputum, and other body fluids. Blood tests may not be helpful.
Victims with tularemia who do not receive appropriate antibiotics may have a prolonged illness with weakness and weight loss. Treated properly, very few people with tularemia die. A 14-day course of streptomycin is effective treatment for tularemia. Gentamicin is also effective. Although tetracycline and chloramphenicol have also been found effective, they are associated with significant relapse rates.
Although laboratory-related infections with this organism are common, human-to-human spread is unusual. Victims do not need to be isolated from others.
An antibiotic given after exposure to tularemia is difficult, because the ideal drug, streptomycin, must be given by injection. Tetracycline is effective after exposure to an aerosol of tularemia if given within 24 hours of the exposure and taken for 14 days.
A vaccine has been developed and used in humans since 1940. In the 1960s, a more purified vaccine was developed. Extensive studies have demonstrated that the vaccine protects humans against the organism released into the air. Immunization with the vaccine prevents the typhoidal type and lessens the effects of the ulceroglandular form of tularemia.