Human African Trypanosomiasis

Overview

Human African trypanosomiasis, also known as sleeping sickness, is a vector-borne parasitic disease. It is caused by infection with protozoan parasites belonging to the genus Trypanosoma. These organisms are morphologically indistinguishable and belong to the T.brucei complex:

T.brucei brucei (animal pathogen)
T.brucei rhodesiense (East African trypanosomiasis)
T.brucei gambiense (West African trypanosomiasis)

All 3 organisms are transmitted by the blood-sucking tsetse fly of the

Glossina genus. The disease is acquired when a human is bitten by a

tsetse fly which has acquired the infection from a previous infected

human or an animal which has harboured the human pathogenic

parasite. T. brucei brucei has no pathological effect in humans. The

two human-affecting subspecies are found in different regions of

Africa, with no overlap in geographical distribution. Tsetse flies are found in in 36 sub-Saharan African countries which have a total population of 65 million people. According to the World Health Organisation (WHO), >98% of reported cases are caused by T. brucei gambiense in West and central Africa, whilst 2% of reported cases are caused by T. brucei rhodesiense in East Africa. In 2013, 6314 cases of sleeping sickness were reported. Figures are believed to be more likely around 20000, as many rural areas and misdiagnosed cases go unreported to WHO. The most recent epidemic began in the 1970s and ended in the late 1990s.

The first stage of sleeping sickness presents with non-specific symptoms including fever, headache and joint pain as the parasite remains in the systemic circulation. These non-specific symptoms commonly result in misdiagnosis. Without treatment, the second stage progresses which has an effect on the CNS as the parasite crosses the blood brain barrier. Symptoms of this second stage include inability to sleep during the night, severe neurological disorders and can lead to coma and death.

Signs and symptoms

The subspecies that cause African trypanosomiasis have different rates of disease progression and the clinical features depend on which parasite is the causative organism.

Causes

The disease is mostly transmitted through the bite of an infected tsetse fly but there are other ways in which people are infected.

Mother-to-child infection: the trypanosome can cross the placenta and infect the foetus.
Mechanical transmission through other blood-sucking insects is possible. However, it is difficult to assess its epidemiological impact.
Accidental infections have occurred in laboratories due to pricks with contaminated needles.
Transmission of the parasite through sexual contact was documented.

At risk groups / risk factors

Displacement of populations
War
Poverty

Diagnosis

Parasite located in body tissue or fluid by microscopy
Microscopic examination of lymph node aspirate
Serological testing
CSF lumbar puncture to determine involvement of the CNS

Treatment

Vaccines / prevention

There is no vaccine or drug for prophylaxis against African trypanosomiasis. Preventive measures are aimed at minimizing contact with tsetse flies. Local residents are usually aware of the areas that are heavily infested and they can provide advice about places to avoid.

Preventative 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.