African Trypanosomiasis, also known as “sleeping sickness”, is caused by microscopic parasites of the species Trypanosoma brucei. It is transmitted by the tsetse fly (Glossina species), which is found only in sub-Saharan Africa. Two morphologically indistinguishable subspecies of the parasite cause distinct disease patterns in humans: T. b. gambiense causes a slowly progressing African trypanosomiasis in western and central Africa and T. b. rhodesiense causes a more acute African trypanosomiasis in eastern and southern Africa. Control efforts have reduced the number of annual cases and for the first time in 50 years, the number of reported cases fell under 10,000 in 2009. In 2017–2018, fewer than 2000 cases were reported to WHO. The number of cases continue to drop and in 2020, fewer than 700 combined cases were reported to WHO; over 85% caused by T.b.gambiense and around 15% caused by T.b.rhodesiense (https://www.who.int/data/gho/data/themes/topics/human-african-trypanosomiasis). Sleeping sickness is curable with medication but is fatal if left untreated.

Two subspecies of the parasite Trypanosoma brucei, T. b. gambiense and T. b. rhodesiense, cause disease in humans, with clinical features of the infection dependent on the subspecies involved.

T. b. gambiense is endemic in western and central Africa, while T. b. rhodesiense is restricted to eastern and southern Africa. Their ranges do not overlap except in Uganda where both subspecies are co-endemic, with T. b. gambiense in the northwest corner of the country along the borders with South Sudan and the Democratic Republic of the Congo, and T. b. rhodesiense mostly clustered in the center of the country.

T. b. rhodesiense (East African sleeping sickness) is found in focal areas of eastern and southeastern Africa. In 2020, fewer than 100 cases of East African trypanosomiasis were reported to WHO (https://www.who.int/gho/neglected_diseases/human_african_trypanosomiasis/en/). Domestic and wild animals are the main reservoir of infection. Cattle have been implicated in the spread of the disease to new areas and in local outbreaks. A wild animal reservoir is thought to be responsible for sporadic transmission to hunters and visitors to game parks. Infection of international travelers is rare, but it occasionally occurs and most cases of sleeping sickness imported into the U.S. have been in travelers who were on safari in East Africa.

T. b. gambiense (West African sleeping sickness) is found predominantly in central Africa and in limited areas of West Africa and accounts for most sleeping sickness in Africa. Although epidemics of sleeping sickness were a significant public health problem in the past, the disease is reasonably well-controlled at present, with less than 600 cases of West African trypanosomiasis reported to WHO in 2020; more than 50% of these were reported by the Democratic Republic of Congo. (https://www.who.int/data/gho/data/indicators/indicator-details/GHO/hat-tb-gambiense). Humans are the most important reservoir of infection, although the parasite can sometimes be found in domestic animals (e.g., pigs, dogs, goats).

Both forms of sleeping sickness are transmitted by the bite of the tsetse fly (Glossina species). Tsetse flies inhabit rural areas, living in the woodlands and thickets that dot the East African savannah. In central and West Africa, they live in the forests and vegetation along streams. Tsetse flies bite during daylight hours. Both male and female flies can transmit the infection, but even in areas where the disease is endemic only a very small percentage of flies are infected. Although the majority of infections are transmitted by the tsetse fly, other modes of transmission are possible. Occasionally, a pregnant woman can pass the infection to her unborn baby (T. b. gambiense). In theory, the infection can also be transmitted by blood transfusion, sexual contact, organ transplantation and accidental laboratory exposure, but such cases are rare and poorly documented.

This information is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the parasites described above or think that you may have a parasitic infection, consult a health care provider.

Causal Agents

“African trypanosomes” or “Old World trypanosomes” are protozoan hemoflagellates of the genus Trypanosoma, in the subgenus Trypanozoon. Two subspecies that are morphologically indistinguishable cause distinct disease patterns in humans: T. b. gambiense, causing chronic African trypanosomiasis (“West African sleeping sickness”) and T. b. rhodesiense, causing acute African trypanosomiasis (“East African sleeping sickness”). The third subspecies T. b. brucei is a parasite primarily of cattle and occasionally other animals, and under normal conditions does not infect humans.

Life Cycle

During a blood meal on the mammalian host, an infected tsetse fly (genus Glossina) injects metacyclic trypomastigotes into skin tissue. The parasites enter the lymphatic system and pass into the bloodstream (1). Inside the host, they transform into bloodstream trypomastigotes (2), are carried to other sites throughout the body, reach other body fluids (e.g., lymph, spinal fluid), and continue the replication by binary fission (3). The entire life cycle of African trypanosomes is represented by extracellular stages. The tsetse fly becomes infected with bloodstream trypomastigotes when taking a blood meal on an infected mammalian host (4), (5) . In the fly’s midgut, the parasites transform into procyclic trypomastigotes, multiply by binary fission (6) , leave the midgut, and transform into epimastigotes (7). The epimastigotes reach the fly’s salivary glands and continue multiplication by binary fission (8). The cycle in the fly takes approximately 3 weeks. Rarely, T. b. gambiense may be acquired congenitally if the mother is infected during pregnancy.

Life cycle image and information courtesy of DPDx.

Infection occurs in two stages, an initial haemolymphatic stage followed by a meningoencephalitic stage after the trypanosomes invade the central nervous system (CNS). However, many of the signs and symptoms are common to both stages, making it difficult to distinguish between the two stages by clinical features alone. First-stage symptoms may be preceded by the development of a trypanosomal chancre at the site of inoculation within two days to two weeks of being bitten by an infected fly (occurs most commonly with T. b. rhodesiense, rarely with T. b. gambiense although chancres are observed with T. b. gambiense in travelers from non-endemic countries). The first stage involves nonspecific, generalized symptoms occurring 1–3 weeks after the tsetse fly bite with T. b. rhodesiense; the incubation period for T. b. gambiense is less well characterized but disease progresses more slowly than that caused by T. b. rhodesiense. First-stage symptoms for both types of sleeping sickness include headache, malaise, weakness, fatigue, pruritis, and arthralgia. First-stage signs can include hepato-splenomegaly, weight loss and intermittent fevers lasting one day to one week. The intervals between fevers can last days or months. Lymphadenopathy, mainly posterior cervical but in some cases axillary, inguinal or epitrochlear, may also occur. Posterior triangle cervical lymphadenopathy, or “Winterbottom’s sign” is commonly seen in T. b. gambiense infections.

T. b. gambiense infection progresses to the second stage after an average of 300–500 days, whereas T. b. rhodesiense infection progresses to the second stage after an estimated 21–60 days. For both types of disease, the stage is determined by examining cerebrospinal fluid (CSF) and observing trypomastigotes. In second-stage disease, invasion of the central nervous system causes a variety of neuropsychiatric manifestations to appear in addition to the first-stage signs and symptoms, with fever occurring less frequently over time. The sleep/wake cycle becomes reversed, hence the common name “African sleeping sickness”, with daytime somnolence, nocturnal insomnia, and sudden urges to sleep. The patient also experiences mental (hallucinations, delirium, anxiety, emotional lability, attention deficit, apathy, aggression, mania, confusion), motor (motor weakness, abnormal tone, gait disturbance, ataxia, tremor, speech disturbances), sensory (paraesthesia, hyperaesthesia, anaesthesia, pruritis, visual problems), and neurologic (abnormal reflexes, seizures, coma) signs and symptoms. Compared to T. b. gambiense, T. b. rhodesiense is more likely to result in endocrine abnormalities such as adrenal insufficiency, thyroid dysfunction and hypogonadism; and cardiac involvement, such as myocarditis, is more severe.

Early diagnosis is difficult because signs and symptoms in the first stage are non-specific and because diagnostic measures are insensitive. Diagnosis requires confirming the presence of the parasite in any body fluid. With T. b. gambiense, it may be difficult to detect trypomastigotes in routine blood smears because parasitemia levels are usually low and variable. The classic approach for diagnosing T. b. gambiense infection is by light-microscopic detection of the parasite in a lymph node aspirate (usually, from a posterior cervical node). Concentration techniques and serial examinations can be used for blood (centrifugation followed by buffy coat examination, mini-anion exchange centrifugation technique, or microhematocrit centrifugation technique). With T. b. rhodesiense, parasitemia is usually higher than with T. b. gambiense and symptomatic patients typically have detectable parasites in the blood. The parasite also may be found in chancre fluid, or bone marrow aspirates.

Reliable serologic testing for T. b. rhodesiense is not available and microscopic detection of the parasite is definitive diagnosis.

Serologic testing for T. b. gambiense is used for screening purposes only and the definitive diagnosis rests on microscopic observation of the parasite. Recently, rapid diagnostic tests for T. b. gambiense infection were developed and introduced to use in the field in endemic countries: the HAT Sero-K-SeT (Coris BioConcept, Gembloux, Belgium) and the SD Bioline HAT 1.0 (Standard Diagnostics, Yongin, South Korea). These tests are more suitable for passive screening and surveillance in fixed health centers in endemic countries that often lack electricity and laboratory infrastructure.

Staging for both T. b. gambiense and T. b. rhodesiense (i.e., assessment of neurological infection) is performed by microscopic examination of CSF collected by lumbar puncture on a wet preparation looking for motile trypomastigotes and white blood cells (WBC). Patients with five or fewer WBC per microliter and no trypomastigotes are considered to be in the first stage, and those with more than five WBCs per microliter or trypomastigotes are considered to be in the second stage. CSF testing is done after a parasitologic diagnosis has been made by microscopic examination of blood, lymph node aspirates, chancre fluid, or bone marrow or when indications of infection are present that justify a lumbar puncture (e.g., clinical signs and symptoms of sleeping sickness or strong serologic suspicion). Isolation of the parasite by inoculation of rats or mice is a sensitive diagnostic method, but its use is limited to T. b. rhodesiense.

Anyone diagnosed with African Trypanosomiasis should be treated, with specific drug and treatment course depending on type of infection (T. b. gambiense or T. b. rhodesiense) and disease stage (i.e., presence or absence of central nervous system involvement). Pentamidine, the recommended drug for first stage T. b. gambiense infection, is available in the United States. The other drugs (suramin, melarsoprol, eflornithine, and nifurtimox when used in combination with eflornithine) used to treat African trypanosomiasis are not commercially available in the United States but can be obtained from CDC. Physicians can consult with CDC staff to obtain these otherwise unavailable treatment drugs.

There is no test of cure for African trypanosomiasis. After treatment, patients should be closely followed for 24 months and monitored for relapse. Recurrence of symptoms will require examination of body fluids, including CSF, to detect the presence of trypanosomes.

There is no vaccine or drug for prophylaxis against African trypanosomiasis. Preventive measures are aimed at minimizing contact with tsetse flies. Local residents in endemic countries are usually aware of the areas that are heavily infested and may be able to provide advice about places to avoid. Other helpful measures include:

• Wear long-sleeved shirts and pants of medium-weight material in neutral colors that blend with the background environment. Tsetse flies are attracted to bright or dark colors, and they can bite through lightweight clothing.
• Inspect vehicles before entering. The flies are attracted to the motion and dust from moving vehicles.
• Avoid bushes. The tsetse fly is less active during the hottest part of the day but will bite if disturbed.
• Use insect repellent. Permethrin-impregnated clothing and insect repellent have not been proved to be particularly effective against tsetse flies, but they will prevent other insect bites that can cause illness.

The World Health Organization has targeted West African trypanosomiasis for elimination as a public health problem by 2020. The final goal will be the sustainable disease elimination by 2030, defined as the interruption of the transmission of West African trypanosomiasis. (https://www.who.int/news/item/25-03-2021-who-validates-cote-d-ivoire-for-eliminating-sleeping-sickness-as-a-public-health-problem). Strategies for elimination of West African trypanosomiasis rests on three strategies: active and passive case finding followed by treatment of the confirmed cases, and vector control to reduce the tsetse population. Reducing the reservoir of infection is more difficult for T. b. rhodesiense, since there are a variety of animal hosts (zoonosis). For this reason, it is not considered feasible to reach total interruption of transmission of East African trypanosomiasis. Vector control is the primary strategy in use but a multisectoral approach (animal health and resource management) is important in reducing transmission.

What is African trypanosomiasis?

African trypanosomiasis disease, also called sleeping sickness, is caused by a parasite. People can get this parasite when an infected Tsetse fly bites them.

Symptoms include fatigue, high fever, headaches, and muscle aches. If the disease is not treated, it can cause death.

Who is at risk?

Tsetse flies are found in sub-Saharan Africa. Travelers spending a lot of time outdoors or visiting game parks in these areas can be bitten by tsetse flies and get infected.

What can travelers do to prevent African trypanosomiasis?

There is no vaccine or medicine that prevents African trypanosomiasis. Travelers can protect themselves by preventing tsetse fly bites.

Prevent tsetse fly bites by taking the following steps:

• Cover exposed skin by wearing long-sleeved shirts, long pants, and hats.
  • Clothing fabric should be at least medium weight because the tsetse fly can bite through thin fabric.
  • Wear neutral-colored clothing. The tsetse fly is attracted to bright colors, very dark colors, metallic fabric, particularly the colors blue and black.
• Avoid bushes during the day; the fly rests in bushes and will bite if disturbed.
• Inspect vehicles for tsetse flies before entering. The flies are attracted to the motion and dust from moving vehicles.
• Although, there is limited evidence that insect repellent works against tsetse flies, you should still use insect repellent as it can prevent other diseases spread by bug bites. Learn more about how to avoid other bug bites.

If you traveled and feel sick, particularly if you have a fever, talk to a healthcare provider, and tell them about your travel. Avoid contact with other people while you are sick.

What is African trypanosomiasis?

There are two types of African trypanosomiasis (also called sleeping sickness); each is named for the region of Africa in which they were found historically. East African trypanosomiasis is caused by the parasite Trypanosoma brucei rhodesiense. West African trypanosomiasis is caused by the parasite Trypanosoma brucei gambiense. Both types of African trypanosomiasis are transmitted by the tsetse fly which is found only in rural Africa.

How is African trypanosomiasis spread?

A person will get East or West African trypanosomiasis if he or she is bitten by a tsetse fly infected with the Trypanosoma brucei rhodesiense or Trypanosoma brucei gambiense parasite respectively. The proportion of tsetse flies that are infected with these parasites is low. The tsetse fly is found only in rural Africa. Occasionally an infected pregnant woman may pass T. brucei gambiense infection to her baby. Other routes of transmission are possible though rare and poorly documented (sexual, blood transfusion and organ transplantation).

Is African trypanosomiasis a serious illness?

Yes. East and West African trypanosomiasis are eventually fatal if not treated.

Where can you become infected with African trypanosomiasis?

East African trypanosomiasis is found in rural parts of Eastern and Southeastern Africa. In 2020, fewer than 100 cases of East African trypanosomiasis were reported to WHO (https://www.who.int/data/gho/data/indicators/indicator-details/GHO/number-of-new-reported-cases-of-human-african-trypanosomiasis-(t-b-rhodesiense)).

West African trypanosomiasis is found in rural parts of central Africa and in a few areas of West Africa. In 2020, fewer than 600 cases of West African trypanosomiasis were reported to WHO; more than 50% of these were reported by the Democratic Republic of Congo (https://www.who.int/data/gho/data/indicators/indicator-details/GHO/hat-tb-gambiense).

What are the signs and symptoms of African trypanosomiasis?

Infection occurs in two stages: a first stage where the parasites are found in the blood and lymphatic system, followed by a second stage after the parasites invade the central nervous system. East African trypanosomiasis is a more acute disease than West African trypanosomiasis, progressing to the second phase within a few weeks. West African trypanosomiasis disease progresses more slowly, with a mean duration estimated at 3 years. With East African trypanosomiasis, a bite by the tsetse fly is often painful and can develop into a red sore, also called a chancre. This reaction is rarely seen with West African trypanosomiasis. Fever, severe headaches, irritability, extreme fatigue, swollen lymph nodes, and aching muscles and joints are common symptoms of sleeping sickness. Some people develop a skin rash. Progressive confusion, personality changes, and other neurologic problems occur after infection has invaded the central nervous system (second stage). If left untreated, the illness becomes worse and death will occur within months.

How soon after infection will I have symptoms of African trypanosomiasis?

For East African trypanosomiasis, symptoms usually occur within 1 to 3 weeks after an infective bite. For West African trypanosomiasis, symptoms may be minimal or intermittent during the first months of infection. They are usually apparent within a few months to a year after getting an infected tsetse fly bite.

What should I do if I think I may have African trypanosomiasis?

If you suspect that you may have African trypanosomiasis, immediately consult with your health care provider. There are several tests that can be done to look for the parasite (e.g., skin biopsy of the chancre, blood tests, and a spinal tap).

What is the treatment for African trypanosomiasis?

Medical treatment of African trypanosomiasis should begin as soon as possible and is guided by the infected person’s laboratory results. Hospitalization for treatment is usually necessary. Follow-up may require lumbar puncture every 6 months (or sooner if symptoms return) for 2 years.

Once infected, am I immune to African trypanosomiasis?

Even if you had the disease once, you can become re-infected.

Who is at risk for contracting African trypanosomiasis?

The tsetse flies that transmit African trypanosomiasis are found in rural areas in endemic countries. They inhabit forests and savannah areas as well as areas of thick vegetation along rivers and waterholes, depending on the species of fly. Travelers to urban areas in those endemic countries are at minimal risk, although transmission has been observed in some urban settings in the past. The flies bite during daylight hours. In areas where the disease is present, most flies are not infected with the parasite that causes African trypanosomiasis, so the risk of infection increases with the number of times a person is bitten by the tsetse fly. The persons most likely to be exposed to the parasite that causes African trypanosomiasis infection are hunters and villagers with infected cattle herds. Tourists and others working in or visiting game parks may be at risk for contracting African trypanosomiasis if they spend long periods of time in rural areas where the disease is present. Since the tsetse flies that transmit African trypanosomiasis are only found in endemic countries within Africa, the disease cannot be contracted within the United States.

Can I take a medication to prevent African trypanosomiasis?

There is neither a vaccine nor recommended drug available to prevent African trypanosomiasis.

How can I prevent African trypanosomiasis and prevent other insect bites?

1. Wear protective clothing, including long-sleeved shirts and pants. The tsetse fly can bite through thin fabrics, so clothing should be made of medium-weight material.
2. Wear neutral-colored clothing. The tsetse fly is attracted to bright colors and very dark colors.
3. Inspect vehicles for tsetse flies before entering. The flies are attracted to moving vehicles.
4. Avoid bushes. The tsetse fly is less active during the hottest period of the day. It rests in bushes but will bite if disturbed.
5. Use insect repellant. Though insect repellants have not proven effective in preventing tsetse fly bites, they are effective in preventing other insects from biting and causing illness.