A 10-year project involving more than 140 scientists around the world has resulted in the successful sequencing of the genetic code of the tsetse fly Glossina morsitans. The fly is the sole carrier of African sleeping sickness or trypanosomiasis, a disease that threatens millions of people across sub-Saharan Africa and devastates livestock.
The international team, led by Yale School of Public Health in New Haven, CT, has also mined the genome data to advance knowledge on the biology of the tsetse fly and the trypanosome parasite it carries, which is responsible for the disease.
The team hopes their work will now spur scientific breakthroughs to eliminate the scourge of African sleeping sickness in sub-Saharan Africa.
Along with the genetic map, which is published in the journal Science, the team has also produced eight research papers, which are published with an editorial and two historical profiles in a special collection across a number of PLOS journals.
Dr. Geoffrey M. Attardo, a research scientist at Yale School of Public Health, and lead author of the Science paper, says publishing the whole genetic code of the tsetse fly is a "major milestone for the tsetse research community and represents years of hard work by scientists." He adds that they hope the "resource will facilitate functional research and be an ongoing contribution to the vector biology community."
African sleeping sickness threatens millions in sub-Sahara
An estimated 70 million people in across sub-Saharan Africa are at risk for sleeping sickness, which occurs in two stages.
The first stage of infection causes fever, headaches, aching joints and itching. The second stage, when the parasite crosses the blood-brain barrier, causes confusion, poor co-ordination and the sleep problems that give the disease its name.
Without treatment, African sleeping sickness is fatal. Also, diagnosis and treatment are difficult, and require specially trained staff to administer them. And while drugs exist, they are expensive and have many undesirable side effects.
In livestock, trypanosome infection causes anemia and weight loss, which can lead to death. The result is billions of dollars of livestock lost every year.
The worst affected countries are Uganda, the Democratic Republic of the Congo and Sudan, but the disease range also includes 30 or more other countries in the region. International efforts have brought disease numbers down in much of the region, but hotspots remain, and armed conflict can cause numbers to rise.
Genetic blueprint is a 'parts list' of the tsetse fly
By unraveling the genetic code of the tsetse fly, the team has essentially produced a "parts list" of the organism. The blueprint contains codes for all the 12,000 genes that control protein activity in the fly.
Giving scientists access to the blueprint is expected to speed up research into the fly's unusual biology and lead to new methods and strategies for controlling the fly.
As well as helping to control the disease, it is hoped the genome map of the tsetse fly will help scientists understand more about evolutionary biology.
The team had to deal with numerous biological, technical and economic challenges in the project. Not unusual for a genome project, they limited the sequencing to a single genetic line - this makes it easier to compile the small fragments of code (each comprising thousands of letters) into large structures (millions of letters).
The tsetse fly genome comprises around 366 million letters of code, which is about one tenth of the size of the human genome.
But while that simplifies matters on the technical front, it complicates them on the biological front, for unlike other flies the tsetse only gives birth to few offspring at a time, and each fly only yields a small amount of genetic material.
When the project started it was laborious and costly to obtain genetic material from the fly, but as techniques improved, it sped up progress.
As well as helping to control the disease, it is hoped the genome map of the tsetse fly will help scientists understand more about evolutionary biology. This is because the tsetse fly is highly unusual among insects in that they have developed unique partnerships with bacteria for several aspects of their biology, and they give birth to live young that have developed to a large size by feeding on specialised glands in the mother.
Insights from mining the tsetse genome
Having the full blueprint of the tsetse genome gives scientists a chance to "mine" the data to find potential weaknesses that might be useful for developing new ways to prevent and treat African sleeping sickness.
The Science and PLOS papers include some examples of the genetic adaptations that allow the tsetse fly to have such unique biology and transmit the disease to humans and animals.
For example, the tsetse fly has developed a unique biological method to source and infect its prey. Different fly species track down their potential hosts either by smell or sight.
The team found a set of visual and odor proteins that appear to drive the fly's behavior when it searches for hosts or mates.
They also found a light-sensitive receptor gene rh5, the "missing link" that might explain why the fly is attracted to blue-black colors. This feature has already been used to make traps to control spread of the disease.
The tsetse fly also has a large array of salivary molecules for feeding on blood. The team discovered one group of genes, the tsal genes, seem to be particularly active in the fly's salivary glands. They may be involved in helping the fly counteract responses from the host to stop bloodfeeding.
Researchers 'happy to finally reach the finish line' of huge project
Serap Aksoy, a professor in the division of epidemiology of microbial diseases at Yale School of Public Health, was instrumental in starting the whole project in the early 2000s, which began with seed funding from the World Health Organization. Costing around $10 million in total, further funds came from several public and private sources.
Prof. Aksoy says they were "very happy to reach the finish line finally," and reiterated the hope that "tsetse research will now enjoy broader participation from the vector community and lead to improved and/or novel methods to eliminate disease."
The Yale team worked closely with colleagues at the Wellcome Trust Sanger Institute in Cambridge, UK, where the genome was sequenced and assembled, plus many other researchers in Europe and Africa.
Dr. John Reeder, Director of WHO's Special Programme for Research Training in Tropical Diseases, says, "This information will be very useful to help develop new tools that could reduce or even eradicate tsetse flies."
In May 2012 Medical News Today reported how scientists created a satellite-guided plan to control the tsetse fly. Using 10 years of NASA satellite images of Kenyan landscape - and by monitoring tsetse movement - a team from Michigan State University developed the plan, which, with unprecedented precision, can provide details on where and when to direct eradication efforts.
Written by Catharine Paddock PhD