Genetic mutations in parasites may lead to global spread of sleeping sickness

Parasites that cause the deadly illness known as sleeping sickness can spread beyond their native Africa as a result of mutations to key genes, a study shows.

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. The research is published in the journal Nature Communications.

Researchers analyzed 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 combating emerging virulent strains of the parasites, the team says.

Professor Keith Matthews, of the University of Edinburgh’s School of Biological Sciences, who co-led the study, said, “Trypanosomes have found ways to expand their geographic range by excluding the tsetse fly from their life cycle. The molecular changes they exhibit can allow us to detect the emergence of these virulent parasites that threaten both cattle and, potentially, humans.”

Dr. Guy Oldrieve, also of the University of Edinburgh’s School of Biological Sciences, the other study co-author, said, “We plan to continue this research and develop a portable diagnostic tool to facilitate detection of future outbreaks in real-time.”