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Haemoglobin plays a role in protecting humans from a species of the trypanosome parasite that infects cattle, scientists say.

The researchers say this sheds light on how humans are resistant to some trypanosome species and could lead to treatments for African trypanosomiasis (sleeping sickness), caused by Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense.

According to the WHO, sleeping sickness kills 60,000 people a year in Sub-Saharan Africa.

The research was published in PLoS Pathogens last week (7 September).

Numerous trypanosome species in Africa cause varying severities of disease in humans and cattle. Humans are resistant to most, including a species called Trypanosoma brucei brucei.

The researchers discovered that when haemoglobin binds to a protein component of a complex called trypanosome lytic factor (TLF) in the laboratory, TLF kills T. b. brucei much more efficiently.

Since the presence of trypanosomes in humans causes haemolysis — the rupture of red blood cells and release of massive amounts of haemoglobin into the blood — the researchers suggest that T. b. brucei can infect humans but is rapidly killed by the TLF complex strongly activated by the released haemoglobin.

As the parasite brings about the haemolysis that makes the haemoglobin available, it effectively brings about its own destruction, says Stephen Hajduk, head of the Department of Biochemistry and Molecular Biology at the University of Georgia in the United States and a researcher on the study.

The team are now creating a mouse model to confirm their theories.

"We are trying to determine the biological relevance of TLF — specifically which proteins play what role in protecting humans from T. b. brucei," says Hajduk.

"Understanding how TLF kills T.b. brucei in conjunction with understanding how rhodesiense and gambiense are protected from TLF will hopefully lead to both human and cattle treatments."

But Sue Wellburn, head of the Trypanosomiasis Research Group at the University of Edinburgh, Scotland, told SciDev.Net that while the research is interesting science, it is unlikely to have a bearing on the treatment of people with sleeping sickness.

"People do not get infected with T. b. brucei," she says. "It is misleading to suggest otherwise — there has never been a report of T. b. brucei infection in a human."

She added that T. b. brucei infection does not present a large threat to most indigenous cattle populations in Africa either, as they exhibit no symptoms. Other species of trypanosome cause serious cattle infection and loss of revenue for farmers.

Link to full paper in PloS Pathogens

Reference: PLoS Pathogens doi 10.1371/journal.ppat.0030129