African trypanosomiasis or sleeping sickness

Sleeping sickness is a disease that is transmitted in tropical Africa by the infective bite of the tsetse fly. The disease, although prevalent in almost all tropical Africa is highly focalized, as is indicated in the accompanying map of Africa, where the white spots represent the presence of the insect vector. In West Africa, left of the dividing line, tsetse flies transmit Trypanosoma brucei gambiense, responsible for a more slowly developing type of disease, the course of which may take several years. In East Africa the causative agent is Trypanosoma brucei rhodesiense. This organism causes a fulminant type of disease that may lead to the death of the host within several weeks to months. Official figures from the World Health Organization state between 10 and 20 000 cases of sleeping sickness per year. However, the deteriorating situation in Central Africa has led to major outbreaks of the disease, with recently hundres of thousands of estimated cases in Zaire / Congo alone.

Click here to see the geographical distribution of tsetse in Africa

Tsetse fly taking a blood meal.

With the infective bite of a tsestse fly, metacyclic trypanosomes present in the proboscis and the salivary gland of the insect are injected into the host, where they develop first in the skin leading to an typical ulceration called the chancre. From there the trypanosomes move to the lymphe nodes and from there they invade the bloodstream.

Member of a medical team analysing stained bloodsmear from suspected patients for the presence of trypanosomes.

Giemsa-stained smear of blood from an experimental animal (rat) infected with Trypanosoma rhodesiense with a very high parasitaemia (2-3 billion tryps / ml). The nucleus and the kinetoplast are clearly stained. The erythrocytes that do not contain any DNA are not stained. There are almost as many trypanosomes as there are red blood cells.

Once in the bloodstream the trypanosomes divide as long slender trypomastigotes of one specific variable antigen type (VAT) until the majority of them are killed by the host's antibodies directed against this VAT. However, a small percentage of them expresses a different VAT and this survives and will establish the next wave of infection and so on, each wave of infection to a new peak of parasitaemia, high fever and malaise. To see a typical course of infection click here. After some time the trypanosomes invade the central nervous system, leading to the typical symptoms of sleeping sickness, such as an altered day and night rithm, a change of character and eventually coma. When left untreated the outcome of African trypanosomiasis is always fatal.

Boy in the streets of an African village suffering from the early symptoms of cerebral trypanosomiasis and a woman with the late stage of the disease.

Treatment of the early phase of the disease is with either pentamidine in West Africa or suramin in East Africa and with organic arsenicals (Arsobal, Melarsoprol, Mel B) for the late stage of the disease. The latter treatment is not without danger and may lead in 5-10% of cases to a fatal encephalopathy.

Trypanosomiasis victim, dying from an acute encephalopathy after treatment of the late stage of trpanosomiasis with the drug melarsoprol.

There are drugs that are widely used for the treatment of nagana or cattle trypanosomiasis such as ethidium, isomethamidium or berenil. These drugs are effective, both for treatment and for prophylaxis, but are supposed to intercalate into the DNA and therefore suspect to be mutagenic and thus cannot be used for the treatment of humans.

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