What is sleeping sickness?

Quick Answer
A parasitic disease caused by protozoa and transmitted to humans by the bites of infected tsetse flies.
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Causes and Symptoms

Sleeping sickness is a vector-transmitted parasitic disease caused by Trypanosoma. These protozoa are transmitted to humans by the tsetse fly, genus Glossina, which is found only in moist savannas and forests in parts of sub-Saharan Africa. Rarely, transmission can occur from a mother to her unborn child or through blood transfusion or organ transplantation. There are two types of sleeping sickness. West African trypanosomiasis is found in both Central and West Africa. Also called Gambian sleeping sickness, it is caused by Trypanosoma brucei gambiense. East African trypanosomiasis is caused by T. brucei rhodesiense. Another human form of trypanosomiasis, Chagas disease, is found in the Western Hemisphere.

Symptoms of the East African type emerge in three stages. Untreated victims of this acute form of the illness may die within weeks or one year later. The first stage begins with the reaction to the tsetse fly’s bite. A painful sore, called a chancre, appears about forty-eight hours after the bite and lasts from two to four weeks. It is accompanied by swollen lymph nodes. The second or early stage includes high fever, severe headache, joint pain, and fatigue; symptoms appear in waves, with symptom-free periods that can last up to two weeks. Rashes, swollen lymph nodes, enlargement of the liver and spleen, and edema may also occur. As the disease progresses, weight loss and debilitation increase. Heart involvement may appear early; some patients succumb to heart failure before the parasites invade the central nervous system. In the late stage, which appears within a few weeks to months of the infection, loss of appetite, personality changes, headache, listlessness, and insomnia are seen, along with tremors, slurred speech, and unsteady gait. Uncontrollable drowsiness occurs late in the course of the disease, progressing to coma and finally death, often from secondary infections.

West African sleeping sickness is a chronic illness, though just as deadly as the East African variety if left untreated. Instead of three distinct stages, there is usually a long symptom-free period. Often, no chancre appears, and the early stage may be so mild as to be overlooked, although swollen lymph nodes on the back of the neck, called Winterbottom’s sign, may be visible. Symptoms gradually appear weeks or years later but are often so subtle that they continue to be ignored. Ironically, the lack of symptoms can be very dangerous for the patient because early treatment of sleeping sickness is critical in avoiding disability or death.

Treatment and Therapy

Most of the drugs used to treat sleeping sickness are highly toxic. Mortality from drug toxicity can reach 5 to 10 percent. In addition, some of the drugs cannot cross the blood-brain barrier, so they are useless in late-stage illness. One nontoxic drug, eflornithine, not only crosses the barrier but also is highly effective in treating both early-stage and late-stage West African infection. It is not used for East African illness, however, because it is not consistently effective for that type. In addition, it is expensive and difficult to administer correctly. Thus, for both types of early-stage infection, intravenous suramin (or suramine) is often used after giving a test dose to see how patients will tolerate the drug, with intravenous melarsoprol given for late-stage disease of both types. With treatment, most patients recover. However, irreversible brain damage or death is common when therapy is attempted at the later stage.

Perspective and Prospects

Sleeping sickness is endemic in about one-third of Africa’s total land area and threatens more than sixty million people in thirty-six countries. The World Health Organization (WHO) previously estimated that between 300,000 and 500,000 people were infected annually, despite much smaller numbers of cases reported. Efforts to control the disease have since led to a drop in cases—since 2009, less than 10,000 cases have been reported annually, and WHO's estimate of actual annual cases has dropped to 30,000. In some areas of Angola, the Democratic Republic of Congo, and southern Sudan, sleeping sickness became the first or second greatest cause of mortality during an epidemic of the disease, ahead of human immunodeficiency virus (HIV) or AIDS. Its worst effects are felt in remote, rural areas where health infrastructure is often nonexistent. War, poverty, and lack of education hamper efforts at controlling the disease by shrinking tsetse fly populations through insect abatement programs, treating livestock harboring the parasites, and testing and treating asymptomatic human carriers.

Suramin was discovered in 1921. Pentamidine, sometimes used in treating the early stage of West African sleeping sickness, was discovered in 1941. Melarsoprol, the last arsenic-based medicine still in use, was discovered in 1949. Eflornithine was registered for use in sleeping sickness in 1990 and is approved in the United States for topical use in removing facial hair. None is an ideal drug, and most are difficult to administer under less-than-ideal conditions. Early diagnosis is likewise not easy or inexpensive.

The tragedy is that sleeping sickness had almost disappeared by the early 1960s, but strict screening and control efforts were allowed to lapse, allowing the disease to reestablish itself and become endemic in many areas. In an effort to once again reverse the spread of the disease, WHO created the Program for Surveillance and Control of African Trypanosomiasis (PSCAT), which unites national programs, nongovernmental organizations, private foundations, universities, regional centers, and donor countries in an effort to reach the common goal of permanent eradication.


Dumas, Michel, Bernard Bouteille, and Alain Buguet, eds. Progress in Human African Trypanosomiasis, Sleeping Sickness. New York: Springer, 1999.

Hoppe, Kirk Arden. Lords of the Fly: Sleeping Sickness Control in British East Africa, 1900–1960. Westport, Conn.: Praeger, 2003.

Lyons, Maryinez. The Colonial Disease: A Social History of Sleeping Sickness in Northern Zaire, 1900–1940. New York: Cambridge University Press, 1992.

"Parasites – African Trypanosomiasis (Also Known as Sleeping Sickness)." Centers for Disease Control and Prevention, Aug. 29, 2012.

Ramen, Fred. Sleeping Sickness and Other Parasitic Tropical Diseases. New York: Rosen, 2002.

"Trypanosomiasis, Human African (Sleeping Sickness)." World Health Organization, Oct. 2012.

Vyas, Jatin M., et al. "Sleeping Sickness." MedlinePlus, Nov. 10, 2012.

World Health Organization. Control and Surveillance of African Trypanosomiasis: Report of a WHO Expert Committee. Geneva: Author, 1998.

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