Picture: THINKSTOCK
Picture: THINKSTOCK

SOUTH African scientists and their international collaborators have sequenced the genome of the tsetse fly, which carries the parasite that causes sleeping sickness.

The research is important not only for its potential to open up new avenues for controlling the disease, but also because it has involved African scientists from the very outset. The genome sequence was published on Thursday April 24 in the journal Science, with a set of related papers in the Public Library of Science (Plos). It is the result of a 10-year collaboration called the International Glossina Genomics Initiative, which included 146 scientists from 18 countries, many in Africa.

"The result has been a better understanding of the tsetse fly genome, a host of scientific papers, a number of which were authored by African scientists, and the creation of a vibrant community of African scientists who work (in this field)," said Winston Hide, professor of bio-informatics at Harvard University and one of the project’s founders. No African scientists had been involved in sequencing the malaria parasite 10 years ago, he said.

Sleeping sickness has been eliminated in South Africa, but it remains a threat in some neighbouring states. An estimated 70-million Africans are at risk of sleeping sickness and the livestock version of the disease, called nagana, kills about 3-million cattle each year.

There is no vaccine and there are limited treatments available, so strategies to control the disease are largely focused on the tsetse fly.

Analysing the genome of the tsetse fly had enabled scientists to identify some of the genes responsible for its unusual biology, which would in turn help to accelerate research aimed at identifying and exploiting its weaknesses, said Prof Alan Christoffels, director of the South African National Bioinformatics Institute and co-author of an editorial published Thursday April 24 by the Public Library of Science.

The tsetse fly has some unique biological features that help it source and infect its prey. It has an advanced sense of smell and sight, and is particularly attracted to blue-black colours. Unlike most insects, which lay large numbers of eggs, the female tsetse fly gives birth to live young that it has nourished with a milk-like substance. It has a unique symbiotic relationship with three different kinds of bacteria, and both males and females feed exclusively on blood.

The researchers identified a set of visual and odour proteins that appear to drive the fly’s key behavioural responses, such as searching for mates. They also found the photoreceptor gene rh5 that explains its attraction to blue-black colours.

The team also found a family of genes in the tsetse fly’s salivary glands, the tsal genes, which help the fly counteract its host’s responses to blood-feeding, such as clotting.

"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," said Dr Serap Aksoy, 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." he said.