The
genome of
Trypanosoma brucei (CL-Brener strain) has been sequenced by
The Institute for Genome Research (TIGR) and
Welcome Trust Sanger Institute.
This organism belongs to the Trypanosoma brucei species complex. Members
of this complex cause disease in humans and in other mammalian species. Humans
are the main reservoir host for T.b. gambiense. Domestic cattle and wild
animals, including antelopes, are the main animal reservoir of
T.b. rhodesiense.
The
two sequencing centers have used different sequencing strategies. TIGR used
seed BAC clones mapped onto particular chromosomes by ESTs and ordered by
restriction or genetic mapping for sequencing of Chromosomes II-VIII. The
Sanger Institute has employed a whole chromosome shotgun approach for
chromosomes I and IX-XI. In addition, both sequencing centres carried out
extensive genome survey sequencing. The latest official release (version
2.0) contained 125 contigs, representing 25.544 Mb, and a new release
containing essentially single sequence contigs (with the exception of
sub-telomeric repeat regions) for each chromosome is expected within the next
month. Annotation of this sequence at WTSI and Sanger predicted 13,321
protein-coding genes.
Disease
Trypanosomiasis
caused by T. brucei species is found in 36 countries in sub-Saharan
Africa. T.b. gambiense is present in foci in the tropical countries of
western and central Africa. T.b. rhodesiense occurs in east Africa,
extending south as far as Botswana. The parasites enter the blood stream via
the bite of blood feeding tsetse flies (Glossina spp.). Inside the human
host, the trypanosomes multiply and are capable of invading most tissues. T.b.
gambiense
causes a chronic illness with onset of symptoms after a prolonged incubation
period of weeks or months. T.b. rhodesiense causes a more acute illness,
with onset a few days or weeks after the infected bite; often, there is a
striking inoculation chancre. Initial clinical signs include severe headache,
insomnia, enlarged lymph nodes, anaemia and rash. In the late stage of the
disease, there is progressive loss of weight and involvement of the central
nervous system. As the parasites invade the central nervous system, mental
deterioration begins, leading to coma and death. Without treatment, the disease
is invariably fatal.
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