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Causes of Trypanosomiasis

Trypanosomiasis is a collection of parasitic diseases caused by trypanosomes. The diseases are endemic to tropical regions, including Africa, Mexico, Central America and South America but are not unknown in the United States. Public health workers in Texas have been found be infected with trypanosomes. The genus Trypanosoma includes three protozoa species that cause disease in humans.

  1. What are trypanosomes?

    • Trypanosomes are flagellated protozoa transmitted by insects. They live in the blood and tissues of human and other mammalian hosts, and their life cycle involves multiple stages. Trypanosomes are transmitted to mammals via insect bites and saliva, encyst in mammalian hosts, circulate in the blood of mammalian hosts and are transmitted back to the insect vector via an insect bite. They reproduce inside the insect, continuing the cycle.

    Trypanosoma cruzi

    • Trypanosoma cruzi causes American trypanosomiasis, also called Chagas disease, and is endemic to Mexico, Central America and South America. This protozoa is transmitted by triatomid and reduviid bugs, which are also called "kissing bugs" because they typically bite human hosts on the face.

    Course of T. cruzi Infection

    • A bug bite, rash or facial edema are early signs of T. cruzi infection. The protozoa are usually present in the blood in the initial phases of the disease but then spread to the heart, liver, spleen, brain and lymph nodes. With severe infection, granulomas form in the brain with cysts, and organs enlarge. Myocarditis, hepatosplenomegaly and enlargement of the esophagus and colon are not uncommon. Cardiac blockages due to organ enlargement and brain damage due to granulomas can cause sudden death.

    T. brucei gambiense

    • T. brucei gambiense causes African trypanosomiasis, also called African sleeping sickness. This protozoa is transmitted by tsetse flies and is endemic to tropical West and Central Africa. The flies prefer to live and nest in shady stream banks, and individuals living or working close to stream banks in these areas are at highest risk for infection. The incubation period ranges from a few days to a few weeks.

    Course of T. brucei gambiense Infection

    • African trypanosomiasis caused by T. brucei gambiense is chronic and often fatal. An ulcer at the site of the tsetse fly bite is usually the first symptom. The disease spreads through the blood stream and infects lymph nodes, causing fever, sore joints and muscles and enlarged lymph nodes. Winterbottom's sign, swelling of the posterior cervical lymph nodes, is also common. Severe disease is characterized by convulsions, paralysis, incontinence and nonresponsiveness. Central nervous system (CNS) damage causes death.

    T. brucei rhodesiense

    • T. brucei rhodesiense is similar to T. brucei gambiense and also causes African sleeping sickness. In contrast to T. brucei gambiense, T. brucei rhodesiense is endemic to eastern Africa and is prevalent in cattle-raising areas. The tsetse flies in these areas breed in the brush, rather than in stream banks. T. brucei rhodesiense has been identified in animal hosts, including cattle, sheep and wild game. Because the life cycle of T. brucei rhodesiense involves an animal reservoir, in addition to an insect vector and mammalian host, T. brucei rhodesiense is more difficult to control than T. brucei gambiense. The incubation period is shorter than that of T. brucei gambiense.

    Course of T. brucei rhodesiense Infection

    • African trypanosomiasis due to T. brucei rhodesiense progresses more rapidly than the African trypanosomiasis caused by T. brucei gambiense. T. brucei rhodesiense infects the CNS early in the course of the disease, and heart and kidney disease are also common. The disease is usually fatal within a year.

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