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DairyPost Africa • May 2014
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.
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 dates 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.
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.