.

Disease. Gambian trypanosomiasis, Mid-African sleeping sickness

Geographic distribution. Tropical West and Central Africa

Infection rate. The incidence of Gambian trypanosomiasis is usually less than 3% in endemic areas.

Life cycle. The main vertebrate host is human. The principal invertebrate hosts are tsetse flies of the Genus Glossina genus. T. gambiense is transmitted to humans by biting of an infected tsetse fly after the cyclic development of the parasite.

Morphology. T. gambiense exists in human as a trypomastigote form. It is elongated spindle-shaped organism with blunt posterior end, and with finely pointed anterior end.

Pathology and clinical symptoms. The disease varies in severity from a mild type to a severe fulminating type resembling that of T. rhodesiense. There may be a local inflammatory sign on the biting site. The acute disease lasts a year and is characterized by irregular fever, headache, joint and muscle pains, and a rash. The lymph nodes including postcervical group are enlarged (Winterbottom's sign). Gradually the chronic phase of the disease ensues, with the development of characteristic central nervous system changes. Diffuse meningoencephalitis and meningomyelitis develop. Evidence of nervous impairment becomes prominent, and develops a terminal sleeping stage. Death ensues either from the disease or from intercurrent infections.

Diagnosis. A definite laboratory diagnosis is made by finding the trypanosomes in the blood, lymph nodes, and bone marrow or spinal fluid. The methods include a direct microscopical examination, cultivation and animal inoculation.

Prevention. Prevention include the reduction of sources of infection, the protection of people from infection, the control of riverine tsetse flies, and chemoprophylaxis with pentamidine.

Comments. A succession of antigenic variants occur in T. gambiense infection. This phenomenon stimulates the output of large quantities of immunoglobulin from the host, most of it is non-specific IgM, with no affinity for the infecting parasite. It may be useful for the presumptive diagnosis of African trypanosomiasis.

Trypomastigote of Trypanosoma sp. on the blood smear (Giemsa stain, 1000x) (B).

Histopathological finding of the brain in African sleeping sickness. The tissue showes edema and perivascular infiltration of glial cells.
HE stained, x400

Brain tissue of an encephalitis patient with African sleeping sickness, showing many morula cells. HE stained, x300.