Sex starvation among a species of parasite which causes the fatal disease African Sleeping Sickness could eventually make the bug go extinct, according to Scottish scientists.

A team of researchers from the University of Glasgow have been examining the single-celled organism Trypanosoma brucei gambiense (T.b. gambiense), which has existed for thousands of years.

Originally an animal parasite, T.b. gambiense ‘jumped’ into the human population within the last 10,000 years, at a time when livestock farming was developing in West Africa.

The team discovered that it reproduces by cloning itself rather than through sexual reproduction - meaning that every version infecting something today is a direct copy of an ancient microbe from the dim and distant past.

And this lack of sex in its life cycle may be leading the bug into an evolutionary dead end which may lead to its eventual extinction.

T.b. gambiense is transmitted to humans by the bite of tsetse flies, and once in the bloodstream can lie dormant for months or years without causing symptoms.

Infected people suffer increasing damage to their nervous system, until they eventually lapse into a come, the symptom which gives sleeping sickness its name.

Although the risk of contacting the infection is small, sleeping sickness kills thousands of people each year in sub-Saharan Africa and there is currently no vaccine against the disease.

Researchers from the University’s Wellcome Trust Centre for Molecular Parasitology in the Institute of Biodiversity, Animal Health and Comparative Medicine spent months that sequencing the genomes of the parasite and discovered it is made up entirely of asexual clones descended from a single ancestor.

The study’s lead author, Dr Willie Weir, said: “We’ve discovered that the parasite causing African Sleeping Sickness has existed for thousands of years without having sex and is now suffering the consequences of this strategy.

“An organism’s genetic blueprint is encoded in DNA packaged within structures called chromosomes. Most organisms have two copies of each chromosome and, through sexual reproduction, the DNA within the chromosomes can recombine randomly, in effect shuffling the deck of DNA cards.

“This process generates genetic diversity and, through natural selection, undesirable combinations and mutations are eliminated from the population, promoting long-term survival of the species.

The team’s research has shown that T.b. gambiense arose from a single individual parasite within the last ten millennia and, over time, mutations have accumulated on each chromosome copy.

Dr Weir added: “Some organisms appear not to have sex at all. Evolutionary theory predicts that they should face extinction in the long-term and that a lack of sexual recombination should leave a characteristic genetic ‘signature’ in their DNA. While being theoretically predicted for almost 20 years, evidence for this signature has been elusive.”

Dr Annette MacLeod, senior author on the paper, believes that the parasite's unusual method of reproduction would likely spell its doom, as it makes it easier to develop drugs which can combat it.

She said: “Essentially, the parasite compensates for its lack of sex by overwriting mutations through ‘copying and pasting’ DNA from one chromosome to another.

"However, our study suggests that this can only go some way to compensating for a lack of sex. Theoretically, this parasite species cannot survive indefinitely without sex and the predicted consequence of this is that it will become extinct in the long-term.

“In the near to medium term, though, identifying this weakness in the parasite could help researchers find ways to develop new forms of treatment for sleeping sickness which build on our findings. For example, the inability of individuals to share genetic information with each other could hamper the ability of the organism to develop resistance to multiple drugs.”