African sleeping sickness parasites strike back
Assisted by Danish researchers, Belgian researchers have discovered how parasites in African tsetse flies cheat an otherwise intelligent immune mechanism in humans to cause the deadly sleeping sickness (trypanosomiasis). The discovery provides more knowledge about how to combat the disease which constitutes a major problem in Africa.
According to the WHO, some 60 million people are threatened by the deadly African sleeping sickness which infects the brain. The disease spreads through bites of the tsetse fly, which leaves parasites in the body. Up to 500,000 people are believed to be infected by the disease. Hopes were therefore raised when Danish and Belgian researchers a couple of years ago discovered a new mechanism in the human immune system which fights some types of the disease.
However, new research from almost the same research team now reveals that the most dangerous type of sleeping sickness parasites can cheat this immune mechanism. Just published in the international journal Nature, the result will contribute to re-evaluate the options for developing an effective treatment.
Parasite adapts to survive
The response from the parasites is the result of millions of years of evolution.
“The sleeping sickness parasite needs parts of our haemoglobin, which carries oxygen and other gases in our blood. We first discovered that the body has developed a mechanism that releases a haemoglobin-binding protein – the so-called haptoglobin-related protein – which brings another substance into the parasite, where it becomes deadly toxic to the parasite. In this way, the body cheats the parasite, which explains why people are resistant to some types of sleeping sickness parasites, for example those causing Nagana, the widespread and serious sleeping sickness in cattle. However, the new research findings now also show that the most dangerous sleeping sickness parasite, which infects humans, has developed its counter move. It absorbs less toxin and may even inactivate the toxin to bypass our otherwise sophisticated immune mechanism and carry on with its undesirable job", says Professor Søren Moestrup from Aarhus University.
No vaccine on the horizon
The researchers have no new therapy in the immediate pipeline, but the new discoveries are an important step in the development of a new medicine to circumvent the parasite's defences, adds Søren Moestrup. Despite the new findings, it may be long into the future before an actual drug can be offered to the Africans.
“We also have to face the fact that it is extremely difficult to get the pharmaceutical industry to invest money in Third World diseases,” says Søren Moestrup.
Denmark has only seen very few cases of sleeping sickness. Tourists travelling in the affected areas in Africa do, however, risk being infected by the disease. Until a vaccine is available, the most effective preventive measure is to avoid tsetse fly bites.
Read the scientific article ‘Mechanism of Trypanosoma brucei gambiense resistance to human serum’
Professor Søren Moestrup, MD
Aarhus University, Department of Biomedicine
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