Dictionary:

trypanosomiasis

  (trĭ-păn'ə-sō-mī'ə-sĭs)

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A disease or infection caused by a trypanosome.

A potentially fatal infection caused by parasites of the genus Trypanosoma.

The African trypanosomes, the cause of African trypanoso-miasis or African sleeping sickness, are flagellated protozoan parasites. Trypanosoma brucei rhodesiense and T. b. gambiense cause disease in humans. Trypanosoma brucei is restricted to domestic and wild animals. The trypanosomes are transmitted by the tsetse fly (Glossina), which is restricted to the African continent. The trypanosomes are taken up in a blood meal and grow and multiply within the tsetse gut. After 2–3 weeks, depending upon environmental conditions, they migrate into the salivary glands, where they become mature infective forms, and are then transmitted by the injection of infected saliva into a new host during a blood meal. The survival of the tsetse fly is dependent upon temperature and humidity, and the fly is confined by the Sahara to the north and by the colder drier areas to the south, an area about the size of the United States. Approximately 50 million people live within this endemic area, and 15,000–20,000 new human cases of African trypanosomiasis are reported annually.

In humans and other mammals the trypanosomes are extracellular. During the early stages of infection, the trypanosomes are found in the blood and lymph but not in cerebrospinal fluid. There are fever, malaise, and enlarged lymph nodes. In the absence of treatment the disease becomes chronic and the trypanosomes penetrate into the cerebrospinal fluid and the brain. The symptoms are headaches, behavioral changes, and finally the characteristic sleeping stage. Without treatment the individual sleeps more and more and finally enters a comatose stage which leads to death. Treatment is more difficult if the infection is not diagnosed until the late neurological stage.

Trypanosoma cruzi, the cause of American trypanosomiasis (Chagas' disease), is predominantly an intracellular parasite in the mammalian host. During the intracellular stage, T. cruzi loses its flagellum and grows predominantly in cells of the spleen, liver, lymphatic system, and cardiac, smooth, and skeletal muscle. The cells of the autonomic nervous system are also frequently invaded. See also Medical parasitology; Parasitology.

Trypanosomiasis, also known as African sleeping sickness, is an infection endemic to sub-Saharan Africa. It is caused by protozoan parasites called trypanosomes, which are spread by the bite of the tsetse fly. There are two subspecies of trypanosomes that infect humans, each causing a different form of the disease. Trypanosoma brucei rhodesiense, found in eastern and southern Africa, causes an acute illness leading to death within weeks or months. Trypanosoma brucei gambiense, found in western and central Africa, causes a more chronic form of the illness which may last several years. Both forms of sleeping sickness are fatal if left untreated.

It is estimated that approximately 60 million people are at risk for the disease. Accurate assessment of the extent of the disease is made difficult by the remoteness of the areas in which it is found and the variability in the tests used for diagnosis. Trypanosomiasis often occurs focally, so scattered pockets of infection will be found within an endemic region.

Following the bite of an infected tsetse fly, a scab, or chancre, often forms. After an incubation period of days to weeks, the trypanosomes enter the blood and lymphatic systems and multiply. During this stage, patients may experience headaches, fevers, sweating, rash, and malaise. Enlargement of lymph glands occurs, particularly at the back of the neck. The enlarged nodes may be the only visible sign during this phase of the infection. Eventually the trypanosomes will invade the central nervous system, giving rise to neurological symptoms. This stage, aptly called "sleeping sickness," is characterized by headache, apathy, lethargy, and somnolence. Patients may experience personality and cognitive changes, tremors, and coordination problems. They become increasingly wasted and drowsy, and eventually fall into a coma and die. This progression to death usually occurs in months with T. b. rhodesiense and in years with T.b. gambiense.

Diagnosis is made by microscopic identification of the parasite, which may be found in the chancre, lymph glands, blood, or cerebral spinal fluid, depending on the stage of the disease. There are several serologic assays available. The sensitivity and specificity of these tests are variable. They are used mainly for epidemiological surveys, but they do have some clinical utility as well.

The form of treatment depends on whether the central nervous system (CNS) is involved. If the disease has not affected the CNS, suramin or pentamidine may be used. In cases of CNS involvement, melarsoprol is the drug of choice. This is a very toxic drug which may have severe side effects, including a fatal encephalopathy. Another effective medication for the treatment of T. b. gambiense is eflornithine. Unfortunately, this drug is not currently readily available.

Human beings are the main hosts of T. b. gambiense. Control of this infection involves routine screening of at-risk populations, treatment of infected individuals, and control of exposure to tsetse flies, which often inhabit riverine areas. T. b. rhodesiense is found in savannah areas in antelopes, other wild game, and domestic cattle, so control of infection is more complicated and involves the coordination of medical, veterinary, agricultural, entomological, and other services.

(SEE ALSO: Comunicable Disease Control; Vector-Borne Diseases)

Bibliography

Burri, C. et al. (2000). "Efficacy of New, Concise Schedule for Melarsoprol in Treatment of Sleeping Sickness Caused by Trypanosoma brucei gambiense: A Randomised Trial." Lancet 355:1419–1425.

Neva, F. A., and Brown, W. (1994). Basic Clinical Parasitology. Englewood Cliffs, NJ: Prentice Hall.

Smith, D. H.; Pepin, J.; and Stich, A. H. R. (1998). "Human African Trypanosomiasis: An Emerging Public Health Crisis." British Medical Bulletin 54:341–355.

World Health Organization (1998). "Control and Surveillance of African Trypanosomiasis." World Health Organization Technical Report Series 881(vi):1–114.

—— (2000). "African Trypanosomiasis." WHO Report on Global Surveillance of Epidemic-Prone Infectious Diseases. Geneva: Author.

— MARTHA FULFORD; JAY KEYSTONE

Clinically a nondescript disease which may be peracute, acute or chronic. Called also nagana, mal de caderas and others. See also dourine, surra. The diagnosis is based on a positive blood smear and the presence of an insect vector, often a tsetse fly, or a history of mating in the case of dourine.

• American t. — a disease of humans caused by infection with Trypanosoma cruzi.

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