Human African trypanosomiasis

The disease

Human African Trypanosomiasis

Also called “sleeping sickness” is caused by a parasite and is fatal if left untreated. Trypanosomes are transmitted by the insect Glossina called the tsetse fly. The disease affects mostly poor populations living in remote rural areas of Africa. Travelers visiting the sub-Saharan part of the continent may also become infected when they travel through tsetse fly habitat. There is basically no risk of sleeping sickness transmission in urban areas; however, peri-urban transmission has been recently described in Kinshasa and Luanda. Following the bite of the infected fly the parasite will multiply in the lymph and the blood causing headaches, fever, weakness, sweating, pain in the joints, and stiffness; over time, it will cross the blood-brain barrier migrating to the central nervous system causing a panoply of neurological disorders including psychiatric disorders, seizures, coma and ultimately death.

People who become infected may or may not show signs of illness immediately. In the case of T.b. rhodesiense infections, the disease is acute, lasting from a few weeks to several months while in T.b. gambiense infections the disease is chronic, generally lasting several years without any major signs or symptoms. However, in both cases without proper diagnosis and treatment the outcome is death.

HAT transmission 2000-2005

WHO estimated that in 2000 that some 50 to 60 million people in Africa were exposed to the bite of the tsetse fly. At that time WHO considered that close to 300 000 children, women, and men on the African continent were affected by the disease, a figure which is much larger then the 27 000 cases diagnosed and treated that year. Since that date much control efforts were made and the population under surveillance was substantially increased. In 2007, the number of new cases reported had already fallen to 10 769 (the Country information page provides more information).

Legend: Legend: Annual number of cases reported to WHO, 2000–2007

Green: No cases reported; Blue: <50 cases reported;
Brown: 50 to 1000 cases reported; Red: >1000 cases reported

When infected individuals remain undiagnosed or diagnosed but untreated they are a source of infection for flies which will become infected when biting them. The parasite will then multiply in the salivary glands of the fly which will spread the infection to the next fly-bite individual thus closing the transmission cycle. Animals can also become infected and harbor the human infective parasites which substantially complicates the transmission cycle since infected animals become parasite reservoirs for the uninfected flies. Commonly, in the case of T.b. rhodesiense transmission the cycle involves wild and domestic animals while in T.b. gambiense the transmission cycle is mostly human to human, involving animals to a much lesser extent.

The T.b. rhodesiense acute infections occur in eastern and south eastern part of the continent. The chronic form of the disease due to T.b. gambiense is found in west, central and south western part of Africa. The distribution of the disease is focal occurring in circumscribed areas. Since the beginning of the 20th century, as soon as the disease was clearly identified and its epidemiology better understood, some 260 foci were described. Today only a number of these foci are recognized active, meaning where transmission is taking place.

Diagnosis

Diagnosis of HAT requires confirming the presence of the parasite. The disease is difficult to diagnose early by both, lack of specific signs and symptoms in the first stage of the disease and lack of sensitivity of the parasitological methods available. Serological tests available today are only useful for screening and establishing suspicion of infection. Confirmation of infection will require the performance of parasitological tests to demonstrate the presence of trypanosomes in the patient. The parasites can be present in any body fluids. However, the number of parasite can be so low (mainly in the gambiense form of the disease) that available parasitological methods may not be sensitive enough to find them. Thus a negative parasitological result in the presence of a positive serological test does not necessarily indicate absence of infection, and tests may have to be repeated over time to achieve diagnosis.

Treatment

Only four drugs are registered for the treatment of Human African Trypanosomiasis : pentamidine, suramin, melarsoprol and eflornithine. None of them are anodyne since all have a certain level of toxicity. Pentamidine and suramin are used in the first or early stage of respectively T.b.gambiense and T.b. rhodesiense infections. Melarsoprol is used in the second or advanced stage of both form of the disease and eflornithine is only used in the second stage of the T.b.gambiense infections since it has been found not to be effective in the disease due to T.b rhodesiense. All four drugs are described in a separate section.

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