The findings reveal that climate change and measures to control populations of tsetse flies, which carry the disease, may drive molecular changes in the organisms that cause sleeping sickness — which can be fatal if left untreated.
The parasites — known as African trypanosomes — are normally transmitted by tsetse flies in sub-Saharan Africa. However, they have evolved to enable them to cause infection without tsetse flies, researchers say.
New strains that directly infect animals have been detected in Asia, South America and southern Europe. There is a risk that the same could happen in forms that affect people, the team says.
Until now, the molecular changes that give rise to these new, more virulent forms of the parasites were unknown.
A team led by scientists at the University of Edinburgh has revealed that changes to key genes have simplified the organism’s life cycle, enabling it to spread beyond its normal geographical range.
Researchers analysed the genetic make-up of more than 80 samples of trypanosomes collected from people, tsetse flies, cows and other animals. The information was used to construct a family tree of different parasite strains.
The team then used a gene-editing tool — called CRISPR-Cas9 — to test whether different molecular changes are involved in the parasite’s evolution to spread without tsetse flies. This revealed multiple mutations in genes that play an important role in their life cycle.
Knowing which genes and specific mutations are involved could be key in identifying and combatting emerging virulent strains of the parasites, the team says.
The study, published in the journal Nature Communications, was supported by the Wellcome Trust, Medical Research Council, Bill & Melinda Gates Foundation and the Flemish Government. It also involved researchers from the University of York, KU Leuven, Institute of Tropical Medicine, Antwerp, and the French Agency for Food, Environmental and Occupational Health & Safety.
