July 14, 2005
Gene Maps May Help Drug Hunt for Parasites
WASHINGTON -- Scientists have mapped the genes of a trio of parasites that sicken and kill millions in poor countries and found they share a surprising amount of DNA, even though they cause markedly different illnesses and are spread by different insects.
The research opens the possibility of finding drugs that would fight all three ancient scourges: African sleeping sickness, Chagas disease and leishmaniasis.
Already, scientists have begun using the gene maps to identify possible vaccine candidates against Chagas disease.
The work, in six research reports to be published Friday in the journal Science, is remarkable not so much for the basic genetics; after all, unraveling the genomes of different creatures has become common.
Instead, it is the attention from teams of international scientists that is unprecedented. Despite their toll, these "trypanosome" parasites largely have been neglected - there are no vaccines and inadequate drugs - because they are mostly a problem of the developing world.
"I sometimes thought I'd never see the day when three small parasites would be so celebrated," Rockefeller University parasite specialist George A.M. Cross wrote in an editorial accompanying the research.
"Because of their distinct evolution, the trypanosomes present a plethora of potential drug targets, and potential drugs are almost certainly languishing in the chemical libraries of pharmaceutical companies," Cross said.
The parasites are:
-- Trypanosoma brucei, which causes sleeping sickness. Spread by the tsetse fly throughout equatorial Africa, this parasite is thought to infect between 300,000 and 500,000 people a year. It is fatal if untreated. Therapies are scarce, can be toxic and often fail if given too late.
-- Trypanosoma cruzi, which causes Chagas disease. It is spread by bloodsucking triatomine bugs, which commonly are known as the "assassin bug" throughout Latin America. Some 18 million people are infected, and 45,000 die annually. Symptoms may not appear for years. There is no cure and the parasite eventually causes heart failure. It also can be spread through blood.
-- Leishmania major, which causes a variety of leishmaniasis, spread by the sand fly. Twelve million people from Latin America to the Middle East are thought to be infected and tens of thousands die from various strains; the Leishmania major strain usually causes disfiguring skin lesions.
First among the Science reports, teams of international scientists independently mapped each parasite's genome.
Next, comparing those maps uncovered 6,200 genes that the three parasites share. Their genetic similarities outweigh their differences, concluded researchers led by the University of Washington and The Institute for Genomic Research in Rockville, Md. That suggests it may be possible to find common treatments.
Finally, University of Georgia scientists are teasing out what proteins the Chagas genes create, illuminating how the parasite infects and finding possible vaccine candidates.
The work was funded by the National Institutes of Health and The Wellcome Trust.