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African Sleeping Sickness, also known as Human African Trypanosomiasis, is a tropical disease that evolves through distinct clinical stages. It ultimately results in meningoencephalitis, coma, and death. This severe illness affects 60 to 70 million people in sub-Saharan Africa, where public health concern is at epidemic level.

The World Health Organization reports that the disease is a major cause of death in many parts of Africa. The disease has hit hard in the Democratic Republic of Congo especially, where 70% of cases have occurred during the past 10 years. In 2015 alone, the DRC had 84% of reported cases.

Sleeping sickness parasites, 3D illustration. Trypanosoma parasites transmitted by tse-tse fly and causing African sleeping sickness. Image Credit: Kateryna Kon / Shutterstock

What Causes African Sleeping Sickness?

Human African trypanosomiasis is caused by Trypanosoma brucei parasites that are spread by the bite of infected tsetse flies. Its transmission is primarily through a single bite from an infected tsetse fly. The parasite can infect humans and other mammals.

Early in the disease, Trypanosoma brucei parasites live in the blood, lymph, and subcutaneous tissues. During this stage, patients experience headaches, joint pain, and fever. If untreated, the parasite next enters the central nervous system (CNS). Once they have invaded the CNS, the parasites cause behavioral changes, cognitive dysfunction such as confusion, and significant sleep disruption.

In addition to being transmitted by the tsetse fly vector, Trypanosoma brucei parasite can be transmitted vertically from mother to child when the parasite invades the placenta. Mechanical transmission may also occur via other blood-sucking insects (eg, mosquitoes), accidental inoculation from needle stick injuries in health care settings, or via sexual transmission. These infection pathways are rare, however.

Who is at Risk for African Sleeping Sickness?

There are two types of African Sleeping Sickness. Each is caused by a different Trypanosoma brucei parasite:

  • Trypanosoma brucei rhodesiense– Prominent in East Africa, this form of the disease is responsible for less than 2% of infections. The illness is characterized by rapid symptom development within a few weeks of infection. In this more severe type of African Sleeping Sickness, parasites easily invade the central nervous system, and death occurs within months.
  • Trypanosoma brucei gambiense – Prominent in West Africa, this form of the disease is responsible for 98% of cases. Initial symptoms include intermittent fevers and headaches, conditions which could be associated with other medical conditions. Given this, there is difficulty in diagnosing African Sleeping Sickness. The diagnosis is usually made when the parasite has reached the central nervous system and the key features of the disease have presented themselves.

Because African Sleeping Sickness occurs in many areas of Africa, only those who travel to the continent or live there are at primary risk for acquiring the condition. There is increased risk for infection in rural African villages where agriculture, hunting, or fishing is a primary activity. Among African countries, nations most at risk for the condition include Chad, Congo, Angola, Malawi, Tanzania, Sudan, Zambia, and Uganda.

Stages of Parasite Development

The 2 subspecies of Trypanosoma brucei parasite cause different manifestations of African Sleeping Sickness. Parasite development begins when the tsetse fly feeds on a mammalian host (eg, human), and metacyclic trypomastigotes are injected into body tissues. When the parasite enters the lymphatic system and bloodstream, the parasite moves through several stages over the course of 3 weeks:

  • Parasites transform into bloodstream trypomastigotes.
  • They are then carried to other locations, where they invade body fluids and reproduced through binary fission.
  • Longer durations of infection are associated with parasite invasion of the central nervous system, where the parasite causes the key symptoms of African Sleeping Sickness.


  • “Trypanosomiasis, human African (sleeping sickness).” World Health Organization.…/trypanosomiasis-human-african-(sleeping-sickness).
  • “African Trypanosomiasis.” Centers for Disease Control and Prevention.
  • “Human African trypanosomiasis.” The BMJ.
  • “Human African trypanosomiasis.” ESAI Access to Medicines.
  • “African Sleeping Sickness.” University of Rochester Medical Center.…/content.aspx.
  • “African Sleeping Sickness and its Mark on the Human Genome: An Evolutionary Tale.” Harvard University Graduate School of Arts and Sciences.

Further Reading

  • All African Sleeping Sickness Content
  • What is African Sleeping Sickness?
  • African Sleeping Sickness Symptoms
  • African Sleeping Sickness Treatments

Last Updated: Nov 25, 2018

Written by

Gaea Marelle Miranda

Gaea graduated from the University of the Philippines, Manila, with a degree in Behavioral Sciences,cum laude . Majoring in psychology, sociology, and anthropology, she approaches writing with a multidisciplinary perspective.

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