AFRICAN TRYPANOSOMIASIS

African Trypanosomiasis, or sleeping sickness, is endemic in 36 countries of sub-Saharan Africa in the areas where tsetse flies (Glossina) are found. Estimates suggest that:

• 50 million people are at risk
• 25,000 new cases occur every year

Without treatment, sleeping sickness is almost always fatal. It has led to the depopulation of many parts of Africa since the epidemic at the beginning of the century.

Sleeping sickness is flow, relatively stable because of increased surveillance and control. Recent episodes of resurgence, however, indicate that serious epidemics could occur again.

Transmission Cycle

The disease is caused by two subspecies of Trypanosoma brucei: T.b. gamhiense and T b. rhodesiense.

A third subspecies, Tb. brucei, is not infective to man, but produces "nagana" in domestic cattle and horses.

Antelopes and other game animals are the major reservoirs of rhodesian sleeping sickness. Gambian sleeping sickness has a manfly-man transmission cycle, but pigs and some game animals may serve as secondary reservoirs.

Different species of tsetse flies favor forests around rivers or lakes, scrub forests, or deep rain forests. Therefore, contact between flies and humans is associated with cultivation, fishing, hunting and collecting firewood.

Symptoms

The main symptoms of both forms of sleeping sickness are intermittent fever and enlarged lymph glands and spleen. In the early stage. During the late stage, when parasites invade the central nervous system (CNS), symptoms include drowsiness, lethargy, blank stares, mood changes, convulsions, slurred speech and paralysis. Without treatment, patients eventually fall into a coma and die.

T.b. rhodesiense is the most virulent form of sleeping sickness. With T. h. gambiense, symptoms do riot appear for months or even years after infection, compared to T. b. rhodesiense, which has an incubation period of only a few weeks.

Economic Impact

Large areas of Africa cannot be settled or used for livestock because of trypanosomiasis. The World Bank reports that animal trypanosomiasis, or nagana, makes livestock production impossible on some 10 million square kilometers in higher rainfall areas, or 45 percent of all land in Sub-Saharan Africa.

African human trypanosomiasis usually strikes working-age adults. The World Health Organization Expert Committee on Trypanosomiasis estimated that the average rural inhabitant would lose 10 years of income, or $615 (1986 U.S. dollars), because of premature death caused by sleeping sickness.

Treatment

Early diagnosis is important because early stage sleeping sickness is easier and less hazardous to treat than late-stage disease.

Suramin is used for treating the early stages of both forms. Pentamidine is effective against early-stage T. b. gambiense. All of these drugs are expensive and have serious side effects. Suramin costs US $8 and pentamidine US $35 per patient.

Melarsoprol, a drug for treating late-stage cases with central nervous system involvement, is expensive (US $133). Its side effects can lead to death and many cases do not respond to treatment.

A new drug, eflornithine, has been field tested successfully against late-stage T.b. gambiense. Over 90 percent of more than 600 patients with late-stage gambian sleeping sickness who had not responded to treatment with melarsoprol have been cured with eflornithine.

Like melarsoprol, eflornithine is expensive and requires weeks of hospitalization. It is not effective against T.b. rhodesiense.

Sleeping Sickness Control

Early control measures based on destroying game and tsetse habitats were effective, but have been abandoned for conservation purposes.

Recently traps have proved an effective tool for tsetse control. Scent-baited traps impregnated with pyrethroid insecticides are very efficient in reducing populations of vectors in both West and East Africa. A pyramid-shaped trap that does not require insecticides has also shown great promise. Traps are inexpensive and, with appropriate training, can be maintained by community members.

Ground spraying of insecticide by professional teams can be effective, but it is costly and rarely employed. Aerial spraying and large-scale ground operations should be used only for acute epidemics.