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 The findings announced on Thursday were the culmination of a
multimillion dollar, decade-long effort involving more than 140
scientists from 78 research institutions in 18 countries.
The fly's bite carries a parasitic microorganism that causes
sleeping sickness in people in sub-Saharan Africa and a form of the
disease in animals that can devastate livestock herds.
Sequencing the tsetse fly's genome exposed the molecular
underpinnings of its weird biology: it gives live birth to young
rather than laying eggs like other insects; it nourishes larvae
inside the uterus with a form of milk; it is oddly attracted to the
colors blue and black; and it feeds exclusively on blood.
The scientists expressed optimism that the genetic blueprint could
lead to new ways to combat the tsetse fly like a chemical that could
interfere with its reproduction or ways to improve existing traps
used to kill it.
"Like any such discoveries, there will be new leads that we might
not see now. I am, however, optimistic that unique aspects of tsetse
fly biology will lead to new methods to fight the disease," said one
of the researchers, Daniel Masiga, a molecular biologist at the
International Centre of Insect Physiology and Ecology (icipe) in
Kenya.
"If you could come up with a tsetse-specific reproductive inhibitor
that has no mammalian toxicity, that would be ideal," added
biologist Geoffrey Attardo of the Yale School of Public Health,
another of the researchers.
The tsetse fly genome was double the size of a fruit fly's but only
a tenth as big as a human's genome. It has about 12,000 genes and
366 million letters of genetic code.
SHEER MISERY
The tsetse fly has brought misery to humans and animals for eons.
They have existed far longer than people; a tsetse fly fossil found
in Colorado date back about 34 million years.
African sleeping sickness, also known as trypanosomiasis, is a
widespread tropical disease throughout sub-Saharan Africa that is
fatal if not treated.
Its form in animals is called nagana. It has caused billions of
dollars in economic damage and has forced farmers to rear hardier
but scrawnier cattle that provide less meat and milk but can better
withstand the parasite, said tropical disease researcher Matthew
Berriman of the Wellcome Trust Sanger Institute in Britain.
The fly is not born with the parasite but ingests it when it bites
an infected person or animal to eat blood. It spreads the parasite
through saliva when it bites another victim.
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In its advanced stages, sleeping sickness targets the central
nervous system, causing alteration of the biological clock
(circadian rhythm), changes in personality, confusion, slurred
speech, seizures and difficulty walking and talking.
"Sleeping sickness threatens millions of people in 36 countries in
sub-Saharan Africa. Many of the affected populations live in remote
areas with limited access to adequate health services, which
complicates the surveillance and therefore the diagnosis and
treatment of cases," said John Reeder, who heads World Health
Organization's program for research and training in tropical
diseases.
In recent years, public health efforts have cut the number of cases
and deaths. The WHO, an agency of the United Nations, said it
considers the disease to be "entering into a phase of elimination."
According to WHO figures, 5,967 cases were reported last year
compared with 26,574 reported in 2000.
Disease prevention has focused on reducing fly populations. Experts
think a preventive vaccine is unlikely because of the way the
parasite evades the mammalian immune system.
Sleeping sickness causes far fewer infections and deaths than the
mosquito-borne tropical diseases malaria and dengue.
In mosquitoes, only females feed on blood, using its protein for egg
development. Both sexes of tsetse flies eat blood.
Experts say tsetse flies may be easier to target than mosquitoes.
For one thing, female mosquitoes can lay more than 100 eggs at a
time while tsetse flies multiply fairly slowly as they give birth to
only one larva per reproductive cycle.
The study was published in the journal Science, with accompanying
research appearing in other journals.
(Reporting by Will Dunham; editing by Toni Reinhold)
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