Despite the efforts to fight Human African trypanosomiasis (HAT), also known as sleeping sickness, it continues to plague several parts of Africa. This disease, fatal if untreated, is caused by parasites called trypanosomes, which are transmitted to humans by the infamous tsetse fly.
In Western Africa, particularly in the mangroves of Guinea or in the Ivory Coast forests, increasingly close contacts between humans and the vector encourage the transmission and the persistence of the disease.
To maximize and target more effectively the difficult and costly fight against the disease, an improved surveillance network has been set up in Africa during the past few years. An IRD1 team based at CIRDES2 in Burkina Faso – which has now been designated as a WHO Collaborating Centre – has developed a state-of-the-art diagnostic method, the immune trypanolysis test3, which helps identify populations at risk and hence pinpoint priority areas for intervention.
This parasitic infection affects predominantly poor and rural populations, so HAT receives little attention from donors and the pharmaceutical industry, and is in effect a neglected disease. After it was thought to be under control in the middle of the 20th century, the disease re-emerged in the 80s, as mass screening was no longer implemented and medical surveillance was poor. Faced with this new epidemic, the measures taken to fight the disease in the late 20th century did help turn this African curse back again.
In 2009, for the first time in the last 50 years, the number of reported cases dropped below the symbolic threshold of 10,000 – compared with nearly 40,000 in 1998. Nevertheless, the disease continues to be a serious public health issue in some regions of Africa.
The tsetse fly (genus Glossina), which transmits the pathogen to humans through bites, flourishes in these environments. The mangroves of Guinea are exploited for their wood, for the extraction of salt, for fishing and for cultivating rice. In the Ivory Coast, the forests are gradually being replaced by cash crop plantations of coffee and cocoa. These pioneer fronts are increasingly affected by human activity and bring humans in much closer contact with the vector, thus encouraging the disease to spread.
To deal with the disease in these areas while avoiding past mistakes which led to its resurgence, the World Health Organization and the African Union have launched a major campaign for the eradication of trypanosomiasis.
The aim is to pinpoint the risk areas so that costly and difficult medical and anti-vector interventions can be better targeted and optimized. In order to do so, Institut de Recherche pour le Développement (IRD) scientists working in collaboration with their partners have recently developed a surveillance tool, the immune trypanolysis test. This laboratory test means a large number of people can be screened for diagnosis. A serum sample collected from a subject is put into contact with the parasite and observed under microscope. If the trypanosomes die as a result, the tested serum contains the corresponding antibodies. In other words, the subject will have been in contact with the pathogen during his or her lifetime.
This very specific technique has now been approved by the WHO. It is more reliable than field diagnostic tools, and is now used routinely at the CIRDES2 in Burkina Faso to test all blood samples collected in Western Africa for the purpose of epidemiological surveillance. The collection of samples onto filter paper, a technique also developed by the team, has simplified the preservation and transport of samples to the laboratory.
In collaboration with the National Sleeping Sickness Control Programme team in Guinea, scientists have also increased the sensitivity of a diagnostic test, the minicolumn4 which helps confirm the presence of parasites in the blood of suspected patients. This method is instrumental in reducing the human reservoir by helping to detect and treat more patients in affected areas. The same team has also been able to identify risk factors associated with the disease5 based on a geographical approach, whilst also highlighting priority intervention areas in any given place.
Although the name of the disease implies the opposite, infected patients do not fall asleep. The disease causes sleep disturbance, but it is often in reality a disturbance in sleep pattern: the patient sleeps during the day and is awake at night. The parasite Trypanosoma brucei first invades the blood, then the host’s nervous system, which is the reason for the disturbance. This is followed by sensory, motor, mental and neurological problems. The few treatments available so far are very toxic and require hospital admission for 3 to 4 weeks.
The state-of-the-art work achieved in this field has led the CIRDES-based IRD team to be selected as a WHO Collaborating Center for research on host/vector/parasite interactions for surveillance and control of Human African Trypanosomiasis. These developments contribute to optimize the efforts to control the disease and help use more efficiently the scarce funds available to eliminate the disease. This is the IRD scientists’ target for the next few years in the mangrove areas of Guinea. This work was conducted in collaboration with scientists from the Institute of Tropical Medicine in Antwerp, the National Control Programs against HAT in Guinea, Burkina Faso and the Ivory Coast, and the technical team of the WHO Collaborating Centre.