Scientists Move Closer to Curing Tsetse Sleeping Sickness

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A tsetse fly feeds on human blood. (Photo: Courtesy)

Scientists have sequenced and annotated the genome of sleeping sickness disease vectors. The study which has been published this month in Science, describes the genetic code for a representative Savannah species of tsetse fly (Glossina morsitans), vectors of protozoan parasites, trypanosomes that cause sleeping sickness in humans and nagana in animals mainly in sub-Saharan Africa. It is estimated that 70 million people are at risk of infection and economic loss in agricultural output runs into several billion US $ per year.

Control of sleeping sickness is hampered by expensive drugs and no vaccine has been developed because the trypanosome parasites have developed mechanism to evade the mammalian immune system. Control methods that target the vector (tsetse fly) include trapping, pesticide treatment and sterile insect technique. It is believed that information contained within the genome will provide valuable resource and accelerate research on tsetse’s unique biology i.e. exclusive blood feeders, give birth to live young, provide nutrition to their young by lactation and endosymbiont relationship with bacteria.

The sequencing of the Glossina morsitans genome started in 2003 when the International Glossina Genome Initiative (IGGI) was established with funding from WHO. About 146 scientists were associated with the ten year collaborative project with 3 scientists’ affiliated to Jomo Kenyatta University of Agriculture and Technology, namely: Dr. Steven Ger Nyanjom and Dr. Johnson Kinyua from Biochemistry Department and Dr. Sheila Cecily Ommeh from the Institute for Biotechnology Research (IBR).

Dr. Nyanjom sets up Ngu trap for the Tese-tses

Dr. Nyanjom sets up Ngu trap for the Tese-tses

The analysis of Glossina morsitans genome focused on identifying and annotating genes that codes for proteins that make up the tsetse fly. The proteins are involved in different aspect of tsetse life cycle and include olfaction (smell), gustation (taste), vision, reproduction, digestion, blood feeding, immunity, metabolism, stress response, symbiotic relationship, hormonal regulation of genes and physiological functions.

“This is just the beginning” says Dr. Steven Nyanjom. “With the sequencing of the tsetse genome, researchers will now have access to the 3 important genomes in the life cycle of sleeping sickness: the human host, the pathogenic parasite (Trypanosoma brucei) and the vector host (G. morsitans)

 “Our group focused on olfaction i.e. how the tsetse identify and locate potential hosts by smell. In tsetse preferred hosts are located and recognized through olfaction and visual cues. The antenna is the main olfactory organ and expresses the olfactory proteins including odorant/pheromone binding proteins, chemosensory proteins and odorant receptors. A total of 116 olfactory proteins were annotated. The olfactory genes could be used to help design potent repellants that would deter the tsetse from biting animals and attractants to be used to lure tsetse into traps,” Dr. Nyanjom adds.

Dr. Ommeh characterized the new findings as great milestone for Bioinformatics research in Africa.

‘The publication and many others to follow shows how a Pan-African approach can help discover, solve and alleviate some of the continent’s pertinent  problems like African Trypanosomiasis” says Dr. Ommeh. “It is also a great achievement for African Bioinformaticians in the continent to publish in the prestigious Science journal which has an impact factor of 31 according to the science citation report of 2012. This further demonstrates the power of forging collaborations especially the “Pan-African Bioinformatics network – ABIONet with most members from Africa present in the author list.”

Dr. Ommeh further encourages, African Universities to fully embrace a curricula with Bioinformatics as a core subject since this applied field in Biology coupled with computer science will give scientists the relevant tools and skills to be able to mine and analyze the available Biodata which is currently being generated in large amounts with the current Next Generation Sequencing – NGS technology.

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Dr. Nyanjom (siting right) and Dr. Ommeh (third right- standing) with other scientists during at tsetse annotation jamboree at ICIPE in May 2008

Dr. Kinyua says, “Transmission of trypanosomiasis involves four interacting organisms: the human host, the insect vector, the pathogenic parasite and the domestic and wild animal reservoirs. Glossina are efficient vectors and are responsible for linking these organisms and any reduction of their numbers should lead to significantly reduced transmission and hence contribute to HAT elimination and the sustainability of control efforts. Recent advances in molecular technologies and the Availability of tsetse fly genomic information could lead to the development of new control strategies aimed directly at the fly or its parasite transmission ability. Beyond disease control, the genome is an important resource for evolutionary biology. Tsetse flies are unique from the majority of other insects in multiple aspects of their biology. The analyses performed by the research groups were used to update the automated predictions and add information to the gene predictions in the database”.

Dr. Kinyua He adds that “the process of annotation is ongoing and information will be continually added to this resource over time. The genome opens a whole other world of research regarding African trypanosomiasis”.

Currently, 5 more tsetse genomes are being sequenced. This will facilitate examination of evolutionary biology and adaptations of tsetse on a genomic level relative to other related insects (e.g. fruit fly and mosquitoes).

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