Genetic researchers have successfully sequenced the genome of the tsetse fly (Glossina morsitans), a bloodsucking insect that transmits the parasite Trypanosoma brucei.
The tsetse fly, Glossina morsitans. Image credit: Alan R Walker / CC BY-SA 3.0.
The tsetse fly is the vector for a potentially fatal disease in people (human sleeping sickness) and livestock (Nagana), throughout sub-Saharan Africa, with an estimated 70 million people at risk of infection.
While there are drugs to combat sleeping sickness, they are expensive, have many undesirable side effects, and are difficult to administer in wide swaths of rural Africa where the disease is most pronounced. Left untreated, sleeping sickness is 100% fatal.
Unlike other disease vectors, such as mosquitoes and sandflies, both sexes of the tsetse fly feed exclusively on vertebrate blood, meaning that all tsetse are capable of spreading the disease.
“Human infections with African trypanosomes can be fatal if left untreated. It has not been possible to develop a vaccine for the disease due to the ability of trypanosomes to evade the mammalian immune system, this coupled with the fact that there are some significant side-effects and reports of growing resistance to current trypanocidal drug treatments means that vector control strategies remain the best hope to eliminate the disease,” said Prof Mike Lehane from Liverpool School of Tropical Medicine
It took nearly ten years and more than 140 scientists from numerous countries to map the genome of this fly.
The tsetse fly, Glossina morsitans, from Meyers Lexikon 1888/90.
The scientists found a set of visual and odor proteins that seem to drive the fly’s key behavioral 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 colors. This behavior has already been widely exploited for the development of traps to reduce the spread of disease.
Tsetse flies have an armament of salivary molecules that are essential for feeding on blood. The scientists found one family of genes, the tsal genes, which are particularly active in the salivary glands of the fly. This allows the tsetse fly to counteract the responses from the host to stop bloodfeeding.
The findings are published in a series of papers under the banner Tsetse Genome Biology Collection in the PLoS journals and a paper in the journal Science.
“This is a major milestone for the tsetse research community. Our hope is that this resource will facilitate functional research and be an ongoing contribution to the vector biology community,” said Dr Geoffrey M. Attardo from the Yale School of Public Health, the lead author of the Science paper.
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International Glossina Genome Initiative. Genome Sequence of the Tsetse Fly (Glossina morsitans): Vector of African Trypanosomiasis. Science, vol. 344, no. 6182, pp. 380-386; doi: 10.1126/science.1249656
