Scientists in Belgium say they have made significant progress in creating a cure for the most common form of sleeping sickness.
The gambiense strain of the trypanosoma parasite causes more than 97% of sleeping sickness cases in western and central Africa.
The parasite is resistant to the proteins the immune system produces to fight the infection.
The Belgium scientists from the Universite Libre de Bruxelles say they have developed a mutant version of the protein, which has shown in early tests that it can kill a wide range of trypanosomes, including gambiense.
According to the World Health Organization, there were 7,197 cases of the sleeping sickness in 2012.
During the study the researchers outlined how gambiense evolved a three-part defence mechanism against the protein apoL1, which is what the immune system uses to fight the parasite.
The protein is usually taken up by the parasite by tricking it into believing that it is beneficial.
The apoL1 protein then embeds itself into the walls of the gut membrane, where it kills the parasite.
However, the gambiense defends itself by creating a protein that stiffens the membranes against the apoL1 protein, which acts as a barrier.
It then makes it more difficult for the parasite to absorb the protein. Failing all this, its last line of defence is the fact that gambiense is able to digest apoL1 quicker than other forms of the parasite, so that it cannot be absorbed by membranes.
Lead author of the research, Prof Etienne Pays, speaking to the BBC said: "The crucial thing here is that apoL1 is still there. It has not been absorbed. It can still be used to kill the parasite."
The mutant strain of apoL1 not only kills gambiense, but can kill all African trypanosomes, pathogenic for humans or for cattle.
Pays added: "Needless to say, this is a promising discovery," he added.
"However, it remains to be seen if this apoL1 variant could be used to treat sleeping sickness. In the blood, this protein could be either unstable or toxic in itself, so more work is needed to appreciate the potential of this finding."
Professor of protozoology at the University of Bristol, Wendy Gibson, who has been studying the evolution of trypanosome, told the BBC: "They’ve finally solved the mystery of how the gambiense has been fighting our defences. It is a meticulous piece of work."
Image: Trypanosoma forms in a blood smear. Image courtesy of CDC/Dr. Myron G. Schultz.