Decoding of tsetse fly genome opens way to new controls
14 July 2014
An international research team from 78 research institutes in 18 countries, has published the DNA sequence of the tsetse fly, the carrier of the sleeping sickness parasite, following a 10-year project .
The tsetse fly, Glossina morsitans, transmits the parasite to humans and pets through its bite. It took ten years of work by some 145 researchers in the consortium to reveal the genome of the vector fly. They also determined its genetic structure and the proteins coded by each gene. Knowing its genome is essential to understanding the biology of the insect.
A unique insect
The tsetse fly is distinct from all other insects in many ways. First, compared to other disease vectors among which only the female bites to feed on blood, both sexes are 'hematophagous'. More surprising, the fly has a very distinctive reproductive method which is comparable to that of mammals. It does not lay eggs but gives birth to developed larva after ten days gestation in its uterus, during which it feeds its offspring with a milky secretion.
Researchers found a set of visual and odour proteins that seem to drive the fly's key behavioural responses such as searching for hosts or for mates. They also uncovered the photoreceptor gene rh5, the missing link that explains the tsetse fly's attraction to blue/black colours. This behaviour has already been widely exploited for the development of traps to reduce the spread of disease.
A neglected disease no longer
Screening and treatment for sleeping sickness, or Human African Trypanosomaisis (HAT), is costly, difficult, and toxic. Preventing the disease by developing a vaccine seems difficult because of the ability of the trypanosome to thwart mammalian immune systems. Therefore, vector control is currently the only means of breaking the transmission cycle for the disease.
Gradually, HAT is becoming a less-neglected disease, mobilising an increasingly large scientific community through studies such as these. Access to its DNA represents a major scientific advance, and will accelerate research on its fundamental biology. It opens the way for new prospects for controlling this vector.
These studies should make new concrete progress possible for the disadvantaged populations that are the victims of this scourge.
"Tsetse flies carry a potentially deadly disease and impose an enormous economic burden on countries that can least afford it by forcing farmers to rear less productive but more trypanosome-resistant cattle." says Dr Matthew Berriman, co-senior author from the Wellcome Trust Sanger Institute. "Our study will accelerate research aimed at exploiting the unusual biology of the tsetse fly. The more we understand, the better able we are to identify weaknesses, and use them to control the tsetse fly in regions where human African trypanosomiasis is endemic."
"Though human African trypanosomiasis affects thousands of people in sub-Saharan Africa, the absence of a genome-wide map of tsetse biology was a major hindrance for identifying vulnerabilities," says Dr Serap Aksoy, co-senior author from the University of Yale. "This community of researchers across Africa, Europe, North America and Asia has created a valuable research tool for tackling the devastating spread of sleeping sickness."
1. International Glossina genome initiative. Genome sequence of the tsetse fly (Glossina morsitans): vector of African trypanosomiasis. Science, 2014, Vol. 344 no. 6182 pp. 380-386. www.sciencemag.org/content/344/6182/380
Associated studies can be found on the PLOS website
Sanger Institute: www.sanger.ac.uk