Tularemia (cont.)

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 United States. This translates into 200 cases per year, almost half of which come from Arkansas, Kansas, Massachusetts, Missouri, and Nebraska. 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. Tularemia does not spread from person to person.

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.

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 include meningitis, bone infection, or infection of the heart.

Source: MedicineNet.com
http://www.medicinenet.com/tularemia/article.htm