Genome offers weapon against sleeping sickness

A tsetse fly

Scientists have sequenced the genome of a bacteria that is essential to the survival of the blood-sucking tsetse fly, which transmits the deadly African sleeping sickness disease. The information could help researchers reduce fly populations and thus halt the spread of the disease, which infects 300,000 Africans a year.

The bacterium Wigglesworthia glossinidia lives in the tsetse fly’s gut, where it produces nutrients required by the fly for its survival and successful reproduction. The tsetse fly itself transmits the deadly parasite Trypanosoma Brucei, which causes sleeping sickness and has a devastating effect on livestock and humans in sub-Saharan Africa.

The disease damages the nervous system, leading to confusion, poor coordination and disturbance of sleep patterns. It is fatal if untreated, but drugs against the disease have a relatively high toxicity and are becoming increasingly ineffective as a result of growing resistance.

Current plans to tackle the disease include a controversial — and expensive — proposal, backed by many African nations and the World Health Organisation, to spray 40 countries with tens of billions of male tsetse flies made sterile through irradiation, with the aim of reducing tsetse populations.

However, the completion of the genome sequencing of W. glossinidia — reported in this month’s Nature Genetics — raises hope of a new way of attacking the disease by disrupting the vital relationship between the bacteria and the fly or, for example, by using the bacteria as a vehicle to express foreign gene produces to impact the development of the parasite.

A team of scientists led by Leyla Akman of the State University of New York sequenced the genome, which is one of the shortest to date, at only 697 kilobases. “Given the pivotal role of W. glossinidia in the fecundity of its host, these data [could] lead to the development of new tsetse control strategies for managing the devastating disease it transmits,” they write.

In an accompanying article in Nature Genetics, Brendan Wren of the London School of Hygiene and Tropical Medicine welcomes the new findings as an important step towards controlling the disease.

“The sequencing of W. glossinidia marks the start of an effort to compile the genetic information of the players in the African sleeping disease cycle,” he says, adding that the genome sequences of the tsetse fly and T. brucei are now required as the basis of an effective intervention strategy against the disease.

At the same time, however, Wren also warns of the danger that scientists could be “seduced” away from research on relatively low-profile disease-related organisms — such as tsetse — toward malaria research, where substantial efforts are now being focused.

“Recent weeks have heralded the most significant step forward in vector-borne parasitology with the publication of the genome sequences of the malaria parasite (Plasmodium falciparum) and its carrier the mosquito (Anopheles gambiae),” he says. “This is in stark contrast to the handful of known tsetse fly genes.”

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Link to Nature Genetics research paper by Leyla Akman et al
Link to Nature Genetics commentary by Brendan Wren

Photo credit: WHO/TDR/Fisher