Trypanosomiasis

Synonyms: Human African trypanosomiasis, Human African trypanosomosis, HAT, sleeping sickness, Animal African trypanosomiasis, Animal African trypanosomosis, AAT, nagana

What is it?

The trypanosomiases are caused by trypanosomes (Trypanosoma spp.) and, in Africa, are mostly transmitted by tsetse flies (Glossina spp.).  Tsetse flies are exclusively found in Africa and their geographical distribution covers most of Sub-Saharan Africa. Tsetse flies are usually found in warm ecosystems and are absent from highlands, deserts and cooler climates. Different species are adapted to different environments: savannah, riverine ecosystem and forest. Tsetse flies are diurnal haematophagous (blood-feeding) insects. Both males and females bite. They become infected when they feed on infected mammals. Trypanosomes are blood parasites (specifically uniflagellate protozoans) which develop and multiply in tsetse flies. Tsetse flies are infective 2 to 5 weeks after an infective blood meal and remain infective for their whole life (3-6 months, depending on weather and the availability of food). Several genera are infective for wildlife, domestic animals and humans. Humans are only affected by Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense. T. b. rhodesiense is found in Eastern and Southern Africa (mostly Uganda, Tanzania and Malawi with some cases reported from Kenya, Zambia and Zimbabwe). T. b gambiense is found in West and Central Africa (mostly in the Democratic Republic of the Congo and, to a lesser extent, in Angola, the Central African Republic, Chad, Congo, Guinea, South Sudanand Uganda, with some cases reported from Cameroon, Côte d’Ivoire, Equatorial Guinea and Gabon). Whereas animals (domestic livestock and wildlife) are the main reservoir hosts for T. b. rhodesiense, humans are the main source of T. b. gambiense infection for tsetse flies.

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CDC (English only)
Drugs for Neglected Diseases Initiative (English only)
MSF Sleeping Sickness (English only)
Tsetse.org (English and French)
WHO factsheet (English, French, Spanish and others)
Simplified video
Animated lifecycle of Trypanosoma brucei in human host
Animated lifecycle of Trypanosoma brucei in tsetse (English only)
MSF Sleeping Sickness (English only)
MSF animation (1'12; English)
New approaches to sleeping sickness - SOS Uganda (8'23; English)
Patients tackling sleeping sickness in Uganda (1'07; English)
SOS project (7'42; English)
SOS project (15'33; English)
SOS project - intervention in animals (6'18; English)
Sleeping sickness secures £1 million (6'10; English)
Technical text
CDC (English only)
The History of African trypanosomiasis (English only)
WHO (English only)
Technical video
Distinguished Lecture Series, Columbia University (13'50; English)

How to recognize it

In humans, African trypanosomiasis causes a two-stage disease. At first, a chancre (a red sore spot or ulcer) at the tsetse bite site will be observed. This local skin reaction is caused by the primary multiplication of trypanosomes under the skin. Trypanosomes then migrate to the blood stream through lymphatic vessels. The second stage of the disease, which occurs once the parasite crosses the blood-brain barrier, affects the central nervous system and causes the classic symptoms of sleeping sickness.

Most patients develop fever, headache, muscle and joint aches, and enlarged lymph nodes within 1-2 weeks of the infective bite. Some people develop a rash. After a variable period lasting from weeks to many months, or even several years, after the initial infection, the parasite invades the central nervous system and eventually causes mental deterioration and other neurologic problems, including nighttime sleep disturbance with daytime sleepiness. T. b. gambiense infection progresses more slowly, causing milder symptoms. In untreated individuals death ensues within months or years for T. b. rhodesiense and T. b. gambiense, respectively.

In humans, trypanosomes can be isolated from blood, lymph node biopsies or cerebro-spinal fluid (spinal aspirate). The abundance of T. b. gambiense in blood can be too low for detection. Isolated trypanosomes can be concentrated by centrifugation before they are observed under the microscope. The stage of the disease must be known to determine the treatment to be given to the patient. Thus spinal aspirates are required to distinguish between stages 1 and 2 of human African trypanosomiasis (HAT).

Molecular tools are available to identify specific DNA that might be present in biopsies. A serological test, the Card Agglutination Trypanosomiasis Test (CATT) is  also available to detect specific antibodies but is only effective for T. b. gambiense.  It is commonly used for mass screening, to identify individuals who might be infected, or in epidemiological studies.

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CDC (English only)
Drugs for Neglected Diseases Initiative (English only)
MSF Sleeping Sickness (English only)
Simplified video
MSF Sleeping Sickness (English only)
MSF animation (1'12; English)
SOS project (7'42; English)
Technical text
Clinical Presentation of T. b. rhodesiense Sleeping Sickness in Second Stage Patients from Tanzania and Uganda (English only)
Focus–Specific Clinical Profiles in Human African Trypanosomiasis Caused by Trypanosoma brucei rhodesiense (English only)
Resources for health professionals: sleeping sickness, CDC (English only)
The best practice for preparation of samples from FTA® cards for diagnosis of blood borne infections using African trypanosomes as a model system (English only)
WHO (English only)
Technical video
Distinguished Lecture Series, Columbia University (14'31; English)

In animals, several species of trypanosomes transmitted by tsetse flies cause a disease called nagana or animal African trypanosomiasis (AAT): Trypanosoma congolense, T.vivax, T.brucei brucei, etc. Some animal species and breeds appear to be more resistant and tolerant than others. As such, wildlife and some indigenous livestock breeds are generally more tolerant. Nagana is usually a chronic wasting disease causing undulant fever and not affecting the central nervous system. In cattle, the coat has a characteristic rough and upstanding appearance and animals lose weight. Animals become listless, lag behind the herd, lose interest in their surroundings, ears and tail hang limply and animals cease to react to biting insects. Some animals die from the disease. T. b. rhodesiense and T. b. gambiense do not cause disease in animals although animals may act as healthy carriers, particularly cattle for T. b. rhodesiense.  Trypanosomiases in animals are confirmed using parasitological or molecular methods as described for humans. Serology is sometimes used in epidemiological studies. However, T. b. rhodesiense and T. b. gambiense are difficult to detect because of their low abundance in animals, their affinity for tissues (making them even less abundant in blood) and their resemblance to other animal trypanosomes. Molecular characterization is the only way to identify them at sub-species level.

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SOS project (7'42; English)

Tsetse flies belong to the order diptera, roughly resembling domestic flies. They are black in color and are slightly larger than domestic flies. They fold their wings completely when they are resting so that one wing rests directly on top of the other over their abdomen. Tsetse also have a long proboscis, which they keep horizontal at rest. Tsetse flies are mostly active at temperatures around 25°C (coolest time of warm days or warmest time of cool days) or after rain. They are more abundant in areas with thick vegetation cover. Captured flies can be characterized (species, sex, age) and tested for trypanosomal infections (by dissection and/or using molecular tools).

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Tsetse.org (English and French)
Technical text
Using molecular data for epidemiological inference: assessing the prevalence of Trypanosoma brucei rhodesiense in tsetse in Serengeti, Tanzania (English only)
WHO (English only)

How to control it

African Human Trypanosomiasis is prevented through the control of tsetse flies and the animal or human reservoir. Transmission of trypanosomosis to humans often occurs when people live or work close to or within forest areas or forested streams.   Farmers, people washing clothes or fetching water at streams, hunters and safari professionals and tourists are more exposed. Deforestation and cultivation contribute to the destruction of tsetse’s habitat.  However, populations of some tsetse species are able to persist in small woodland areas. The wild animal reservoir is difficult to control but domestic animals that are suspected to play a reservoir role in HAT may be treated against trypanosomes, tsetse flies or both to reduce the risk of transmission to humans.  Where humans are the main source of infection, early identification and treatment of infected persons is considered to be the main way of reducing the incidence of HAT.

There is no vaccination against HAT or AAT because the parasite constantly changes its antigenic coat. In endemic areas, animals tend to develop some premunition against animal trypanosomiasis, which enables them to remain healthy with a low number of trypanosomes in their blood.  In animals, chemoprophylaxis is possible (chemoprophylaxis based on isometamidium chloride lasts 2-4 months in animals). Otherwise, control of trypanosomiasis relies on tsetse control and chemotherapy.

A range of different techniques have been developed to control tsetse flies. Aerial and hand/ground spraying of tsetse habitat have been shown to be very effective.  Ground spraying is very labour-intensive and requires considerable organisation.  Aerial spraying is expensive, requires a large scale approach to be effective and needs to be carried out under very strict conditions to be safe and efficient. However, it is the most rapid technique and has been shown to rapidly reduce disease transmission and can be capable of eliminating some isolated tsetse populations.  Stationary and mobile baits are cheaper options but also require careful organization.  Stationary baits consist of traps and insecticide-impregnated targets/screens.  Their effectiveness is based on the attraction of tsetse flies to the black and blue colors and, for some tsetse species, to odor baits. Traps present the advantage of capturing tsetse flies for further analysis. Large deployments are required for impregnated targets/screens to have an effect on tsetse populations but protecting small areas with impregnated targets/screens is also possible.  Insecticide treated fences, placed around animal pens are also effective in protecting livestock and killing tsetse flies.   Insecticides can also be applied directly to cattle, which act as mobile baits. Spraying only the legs and the head is considered to be more cost-effective. The use of insecticide on animals may affect ticks as well.  This can contribute to the control of tick-borne diseases without interfering with their endemic stability in the livestock populations, provided that insecticide is applied only to parts of the animal and at appropriate intervals. Finally, where elimination of an isolated tsetse population is the strategic goal, sterile male tsetse can be released from airplanes.  Their effect is based on the principle that females are fertilized only once in their life. If the fertilization is sterile, the female is not able to produce any offspring for the whole of its life.  This expensive technique is sometimes considered in the final stage of such campaigns, once the tsetse populations have been substantially reduced by other methods, but where these methods have not succeeded in eliminating an isolated tsetse population.   It should be noted that most tsetse populations in Africa are not isolated.  To date, the many efforts to protect non-isolated cleared areas by ‘barriers’ of targets, traps, insecticide treated cattle or aerial or ground-spraying have almost all failed in the long term.  Except in one or two areas on the fringes of the tsetse distribution and habitat, either the barriers have not been sustained, or tsetse flies have reoccupied the cleared areas, or both.

Veterinary trypanocides are widely available in Africa (diminazene aceturate and isomethamidium chloride). They are relatively cheap and efficient. Unfortunately, their efficacy is threatened by the resistance of trypanosomes (mainly animal trypanosomes). Resistance is the result of large scale use of trypanocides, underdosage and insufficient alternation.

Chemotherapy in humans is based on suramin (used for T.b. rhodesiense) and pentamidine (used for T. b. gambiense) for first stage treatment. For second stage treatment, melarsopol (an arsenic derivative, quite toxic, responsible for some 5% mortality in treated patients) is the only drug used for treating T.b. rhodesiense, the zoonotic form of HAT.  Treatment always requires hospitalization, typically between 4 and 8 weeks.  For T. b. gambiense,  eflornithine  and a combination of eflornithine and nifurtimox are increasingly used to replace melarsoprol. . The effect on trypanosomes in the CNS is monitored by CNS punctures. Resistance has been reported against some of these drugs.

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CDC (English only)
Drugs for Neglected Diseases Initiative (English only)
MSF Sleeping Sickness (English only)
Stamp out sleeping sickness (English only)
Tsetse.org (English and French)
WHO factsheet (English, French, Spanish and others)
WHO programme to Eliminate Sleeping Sickness: Building a Global Alliance 2002 (English only)
Simplified video
3V Vets: Spraying cattle (1'36; English)
MSF Sleeping Sickness (English only)
SOS approach (1'07; English)
SOS project (7'42; English)
SOS project (15'33; English)
SOS project - Involvement of students (2'46; English)
SOS project - intervention in animals (6'18; English)
SOS project - private sector (1'49; English)
Sleeping sickness in Kaberamaido, Uganda - SOS (5'55)
The SOS model in Nigeria (9'18; English)
The SOS model in Nigeria (9'18; English)
WHO Conference (3'25; English only)
Technical text
Available drugs for chemotherapy African trypanosiasis (English only)
Challenges of controlling sleeping sickness in areas of violent conflict: experience in DRC (English only)
Report of a WHO Informal Consultation on sustainable control of human African trypanosomiasis (English only)
Resources for health professionals: sleeping sickness, CDC (English only)
Spatial Predictions of Rhodesian Human African Trypanosomiasis (Sleeping Sickness) Prevalence in Kaberamaido and Dokolo, Two Newly Affected Districts of Uganda (English only)
The Burden of Human African Trypanosomiasis (English only)
The History of African trypanosomiasis (English only)
The innovation trajectory of sleeping sickness control in Uganda: research knowledge in its context (English only)
Using molecular data for epidemiological inference: assessing the prevalence of Trypanosoma brucei rhodesiense in tsetse in Serengeti, Tanzania (English only)
WHO (English only)
Technical video
Distinguished Lecture Series, Columbia University (14'31; English)

Cultural and geographical specificities

Pastoralist communities

In many parts of Africa pastoralists have traditionally avoided grazing their animals in tsetse-infested areas.  However, many pastoralist communities live in tsetse infested areas.  Either as a result of this or while temporality grazing in tsetse-infested areas, their livestock sometimes suffer from trypanosomiasis.  However, zoonotic trypanosomiasis in humans is rare.

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Communities in northern Africa and the Sahel region

While there are no tsetse flies and no trypanosomes in Northern Africa, extensive parts of the Sahel region are infested.  However, within the region the zoonotic form of trypanosomiasis is absent.  Several ancient foci of the anthroponotic form exist, but no cases have been reported from any Sahelian countries for over a decade.

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Mixed farming communities in more humid regions

Animals act as reservoir of T. b. rhodesiense, the zoonotic form of HAT in eastern and southern Africa, justifying interventions targeting animals to reduce the transmission to humans.  Since tsetse flies are vectors of human and animal trypanosomes, controlling them in this area benefits both human and animal health. Insecticide treatments of animals reduce the abundance of tsetse flies, which may have a direct impact on human health. Insecticide treatments of animals may also reduce the abundance of ticks and the incidence of tick-borne diseases, but, as discussed above, care must be taken to maintain the endemic stability of tick-borne diseases in livestock.  Where wildlife are scarce, in the absence of tsetse control, the proximity of livestock may increase the abundance of tsetse flies and human exposure. Yet, in the absence of animals, tsetse flies will have no other choice than to feed on humans, so it is also argued that livestock could have a protective effect.  Disease modelling is providing some answers to some of these questions and strongly indicates that in these areas treating cattle with trypanocides and spraying them with insecticides has a strong effect in reducing the incidence of zoonotic HAT.

Simplified text
Stamp out sleeping sickness (English only)
Tackling Africa's deadly sleeping sickness, BBC news (English only)
Simplified video
3V Vets: Spraying cattle (1'36; English)
SOS project (7'42; English)
SOS project - Involvement of students (2'46; English)
SOS project - intervention in animals (6'18; English)
SOS project - private sector (1'49; English)
Sleeping sickness in Kaberamaido, Uganda - SOS (5'55)
Stamping out Sleeping Sickness - interview with a politician (1'06; English)
The SOS model in Nigeria (9'18; English)
The SOS model in Nigeria (9'18; English)
Technical text
Burden of rhodesiense sleeping sickness in Uganda (English only)
From research into use: Monitoring and evaluation of a public-private partnership, Stamp out sleeping sickness case study (English only)
Quantifying the Burden of Rhodesiense Sleeping Sickness in Urambo District, Tanzania (English only)
Report of a WHO Informal Consultation on sustainable control of human African trypanosomiasis (English only)
Spatial Predictions of Rhodesian Human African Trypanosomiasis (Sleeping Sickness) Prevalence in Kaberamaido and Dokolo, Two Newly Affected Districts of Uganda (English only)
The Burden of Human African Trypanosomiasis (English only)
The Stamp out sleeping sickness campaign in Uganda: An institutional and policy study (English only)
The innovation trajectory of sleeping sickness control in Uganda: research knowledge in its context (English only)