Merck Manual

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African Sleeping Sickness

(African Trypanosomiasis)


Richard D. Pearson

, MD, University of Virginia School of Medicine

Last full review/revision Oct 2019| Content last modified Oct 2019
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African sleeping sickness is an infection caused by the protozoa Trypanosoma brucei gambiense or Trypanosoma brucei rhodesiense. It is transmitted by the bite of a tsetse fly.

  • Sleeping sickness occurs only in equatorial Africa.

  • A painful bump or sore may form at the site of the fly's bite, followed by fevers, chills, headache, swollen lymph nodes, sometimes a rash, and eventually drowsiness, problems with walking, and, if untreated, coma and death.

  • Doctors usually confirm the diagnosis by identifying the protozoa in a sample of blood, fluid taken from a lymph node, or cerebrospinal fluid.

  • All infected people should be treated with one of several drugs effective against Trypanosoma.

Sleeping sickness occurs only in parts of equatorial Africa where tsetse flies live. There are two forms of sleeping sickness. Each is caused by a different species of Trypanosoma. One form (caused by Trypanosoma brucei gambiense) occurs in West and Central Africa. The other form (caused by Trypanosoma brucei rhodesiense) occurs in East Africa. Both occur in Uganda. There has been a dramatic decrease (> 95%) in the number of reported cases of African sleeping sickness over the past 20 years as a result of control efforts, and the disease has been targeted for eradication by the World Health Organization. On average one case is diagnosed in the United States each year.

Another species, Trypanosoma cruzi, is endemic in South and Central America and causes Chagas disease (American trypanosomiasis).


Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense are usually transmitted to people when an infected tsetse fly bites them and injects the protozoa into the skin. The protozoa move to the lymphatic system and bloodstream, where they multiply. They then travel to organs and tissues throughout the body and eventually reach the brain. The infection is spread when a fly bites an infected person or animal, then bites another person.

An infected mother can transmit the protozoa to her baby during pregnancy or delivery. Rarely, people are infected through blood transfusions. Theoretically, the infection could be transmitted through an organ transplant from an infected donor.


In African trypanosomiasis, different parts of the body are affected in the following order:

  • Skin

  • Blood and lymph nodes

  • Brain and cerebrospinal fluid (the fluid that surrounds the brain and spinal cord)

How quickly the infection progresses and which symptoms it causes depend on which species is the cause.


A bump may develop at the site of the tsetse fly bite within a few days to 2 weeks. It turns dusky red and may become a painful and swollen sore.

Blood and lymph nodes

The infection spreads to the blood and lymph over a period of weeks or months. Then people have fevers that come and go, chills, headaches, and muscle and joint pain. The face may swell temporarily. In some people, a rash develops, and lymph nodes along the back of the neck enlarge. Anemia may develop.

Brain and cerebrospinal fluid

When the brain and cerebrospinal fluid are affected, headaches become persistent. People become drowsy, lose their concentration, and have problems with balance and walking. Drowsiness worsens, and people may fall asleep in the middle of activities.

Without treatment, damage to the brain progresses, leading to coma and death. Death occurs within months or within 2 or 3 years after symptoms develop, depending on the species causing it. Death sometimes results from undernutrition or other infections.


  • Examination of a sample of blood or fluid from a lymph node

  • Spinal tap and analysis of cerebrospinal fluid

Doctors diagnose African trypanosomiasis by examining a sample of blood or fluid from a lymph node and identifying the protozoa in it. Sometimes doctors check for the protozoa by examining a sample of bone marrow or fluid from the sore.

Doctors do a spinal tap (lumbar puncture) to obtain a sample of cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) to determine whether the infection involves the cerebrospinal fluid and brain. Doctors check the fluid sample for the protozoa and for other signs of the infection. Such signs include increases in the fluid's pressure and in the number of white blood cells in the fluid.


People can reduce their chances of being bitten by a tsetse fly by doing the following:

  • Avoiding areas that are heavily infested with tsetse flies: Travelers to parts of Africa where tsetse flies live can ask local residents about places to avoid.

  • Wearing heavy long-sleeve tops and long pants: Tsetse flies can bite through thin clothes.

  • Wearing neutral-colored clothing that blends in with the environment: Tsetse flies are attracted to bright or dark colors.

  • Using insect repellents as needed, although they may not be effective against tsetse flies.


  • Drugs that are effective against these protozoa

Treatment of African sleeping sickness varies by species and stage of disease.

Sleeping sickness should be treated as soon as possible with drugs that are effective against these infections. However, some of the drugs can have serious side effects.

The drug used depends on which species (gambiense or rhodesiense) is causing the infection and whether the infection has spread to the brain and cerebrospinal fluid.

If the infection has not spread to the brain and cerebrospinal fluid, effective drugs include

  • Suramin (for rhodesiense)

  • Pentamidine (preferred for gambiense); suramin is an alternative

These drugs are given by vein (intravenously). Pentamidine may also be injected into a muscle.

If the infection has spread to the brain and cerebrospinal fluid, effective drugs include

  • Melarsoprol

  • Eflornithine (only for gambiense)

  • Nifurtimox in combination with less frequent doses of eflornithine in areas of Africa where frequent dosing of eflornithine is logistically difficult (only for gambiense)

These drugs are given intravenously.

Melarsoprol can have serious, sometimes life-threatening side effects, but in many African countries, it is often the only drug available for sleeping sickness that affects the brain. Corticosteroids may be given to reduce the risk of some of these side effects.

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