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Tsetse Fly Genome Breakthrough: FAO and IAEA Crack the Code

A pregnant female of the tsetse species Glossina morsitans

A pregnant female of the tsetse species Glossina morsitans.(Photo: Geoffrey M. Attardo, Research Scientist, Yale School of Public Health)

With the recent breakthrough in cracking the genome of the tsetse fly species Glossina morsitans, another milestone has been achieved in helping to solve a problem that has had horrendous ramifications for the African region.

Tsetse flies, large biting flies, which populate most of mid-continental Africa between the Sahara and the Kalahari deserts, are vectors for the single-cell parasites also known as trypanosomes. This specific parasite causes trypanosomosis, the sleeping sickness in humans. Konstantinos Bourtzis, a Molecular Biologist with the Joint FAO/IAEA Division, explained the potential gravity of the tsetse bite for human health, for which a vaccine is not available and for which costs of medical treatment are very high. He mentioned that currently, approximately 70 million people face the risk of sleeping sickness, while over 50 000 people are estimated to be infected. Sleeping sickness attacks the central nervous system, changes the biological "time clock", and causes changes in personality including confusion, slurred speech, seizures and difficulty in walking and talking.

Livestock on the other hand, can be hit by nagana, a wasting disease that is transmitted when the tsetse flies bite animals to feed on their blood. Nagana is the root cause of a debilitating chronic condition that reduces fertility, weight gain, meat and milk production, and makes livestock too weak to be used for ploughing or transport, which in turn affects crop production. It results in the yearly death of 3 million animals, with over 50 million animals facing the risk of infection. For African farmers, the tsetse flies are a nightmare to their livelihood; they also impact food security and the socio-economic progress in sub-Sahara Africa.

Finding a solution over the years to the havoc created by tsetse flies to livestock, has been a major challenge to the combined scientific efforts of the International Atomic Energy Agency (IAEA) and United Nations Food and Agriculture Organization (FAO), with the World Health Organization (WHO) focusing on combating human sleeping sickness.

Conducting joint research over the last decades to block to the spread of severe infection from tsetse flies resulted in the introduction by the FAO and IAEA of the well-established environment-friendly Sterile Insect Technique (SIT), a biologically-based method for the management of key insect pests of agricultural, medical and veterinary importance in Africa. A form of insect birth control, SIT involves releasing mass-bred male flies that have been sterilized by low doses of irradiation into infested areas, where they mate with wild females. These do not produce offspring and, as a result, the technique can suppress and, if applied systematically on an area-wide basis, eventually eradicate populations of wild flies. The new acquired knowledge of the genome provides wealth of information for the improvement of the entire SIT package and can help unravel interactions between tsetse flies, symbionts and trypanosomes. The decoding of the genome was detailed in a press release issued by the IAEA recently.

The successful unravelling of the tsetse fly genetic code has been part of an international collaboration that involved the Joint FAO/IAEA Insect Pest Control Laboratory and the support of over 140 scientists worldwide. This scientific breakthrough will enable a better understanding of the biological and genetic potential of the tsetse flies including their nutrition, reproduction, immunity and vectorial capacity, explained Bourtzis.

Bourtzis further elucidated that this discovery will enable scientists to enhance the SIT by integrating it with new and complementary methods in an area-wide approach to control the devastating impact from tsetse flies on animals and humans and that the purpose of developing solutions is not to eliminate a tsetse species but to eradicate local populations of tsetse flies.

Tsetse flies have been successfully eradicated in 1997 from the Tanzanian island of Zanzibar using the SIT. Ethiopia and Senegal are making significant progress in infested areas with the same method. The FAO and IAEA are helping 14 countries control tsetse populations applying area-wide integrated pest management approaches.

Background

Tsetse flies are known to have established sophisticated symbiotic associations with three different symbiotic bacteria. All tsetse fly species examined to date harbour an obligate symbiont of the genus Wigglesworthia, which has a long-lasting symbiotic association with tsetse flies providing them important nutrients, such as vitamins, which are not available in the human and animal blood.

Tsetse flies have also established a symbiotic association with another bacterium, namely Sodalis. Recent experimental work suggests that both tsetse fly midgut-associated symbionts (Sodalis and Wigglesworthia) can affect trypanosome development and thus they can be exploited in order to prevent the establishment and transmission of these parasites.

Tsetse's third symbiont is the alphaproteobacterium Wolbachia. This bacterium is the most successful symbiont on Earth since it infects more than 40% of all insect species. Wolbachia is known to manipulate the reproductive properties of its hosts most commonly causing cytoplasmic incompatibility, a kind of male sterility. Recently in mosquitoes, it has been shown that this symbiont prevents the establishment and transmission of major human pathogens that cause such diseases as dengue, chikungunya and malaria. Whether Wolbachia can also prevent the establishment and transmission of African trypanosomes in tsetse flies, thus blocking the spread of sleeping sickness and nagana, is currently under investigation. Interestingly, the deciphering of the genome of Glossina morsitans, also unravelled the presence of hundreds of Wolbachia genes in the tsetse fly genome. The potential function of these genes, if any, is as yet unknown.


- By Aabha Dixit, IAEA Office of Public Information and Communication

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