A parasite that causes the African sleeping sickness has not had sex in more than 10,000 years, according to new research.
Researchers from Glasgow University’s Wellcome Trust Centre for Molecular Pathology found that the parasite species known as Trypanosoma brucei gambiense, is entirely made up of asexual clones that came from one ancestor.
‘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,’ the study’s lead author Dr. Willie Weir said.
‘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,’ Dr. Weir said.
‘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.
‘However, some organisms appear not to have sex at all.’
Dr. Weir suggested this meant the parasite could be extinct in years to come.
‘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,’ he said.
The African sleeping sickness parasite kills more than 6,000 people a year in sub-Saharan Africa where it is transferred from one person to another by a bite from the tsetse fly.
The World Health Organization states those most exposed to the tsetse fly live in rural areas and depend on agriculture, fishing, animal husbandry or hunting.
In the first stage, the parasite multiplies in the blood and lymph. This is also called haemo-lymphatic stage, which leads to symptoms of fever, headaches, joint pains and itching.
In the second stage the parasites cross the blood-brain barrier to infect the central nervous system. This is known as the neurological or meningo-encephalic stage.
More obvious signs and symptoms of the disease appear including changes of behaviour, confusion, sensory disturbances and poor co-ordination. Disturbance of the sleep cycle, which gives the disease its name, is an important feature. Without treatment, sleeping sickness is considered fatal although cases of healthy carriers have been reported.
The sleeping sickness can be treated with medication.