Scientists decode deadly parasite genomes

Published Jul 15, 2005

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By Maggie Fox

Washington - Three parasites that sicken or kill millions of people in the developing world every year have been genetically sequenced and are giving up clues that could be used to fight them, scientists said on Thursday.

The international team said they had mapped out the genomes of the parasites that cause African sleeping sickness, Chagas disease and leishmaniasis, which kill 150 000 people a year and cripple many more.

They found a "common core" of genes that ties the three together and might pave the way for the development of new drugs or vaccines.

Sleeping sickness, or human African trypanosomiasis, reduces victims to a zombie-like state. Chagas disease damages the hearts and other internal organs of millions of Latin Americans, while leishmaniasis, also known as kala azar and "Baghdad boil," causes fever, a swollen spleen and disfiguring lesions.

Each is spread by a different insect or bug but it turned out they are genetically related - and this could be a weakness that science can exploit, the researchers report in Friday's issue of the journal Science.

All three parasites share about 6 200 genes.

"The basic building blocks of all three parasites are now known," said Matthew Berriman of Britain's Sanger Institute.

"This common core of genes is extremely important because it may provide targets for a new generation of drugs that might fight all three parasites, which threaten millions of people worldwide," said Najib El-Sayed, a molecular biologist at The Institute for Genomic Research who worked on the genome-decoding projects.

"At the moment, there are no vaccines and only a few inadequate drugs to fight these devastating and neglected diseases."

Nearly 250 researchers from 46 organisations representing 21 countries worked on the three studies. Scientists usually compete on such projects, but genome research is an exception.

"Now that the genes of these parasites are mapped out, it's much easier to identify genes that are critical for parasite survival," said Seattle Biomedical Research Institute researcher Peter Myler.

"The core genome of all three is very similar with the differences mainly at the end of chromosomes. So that tells us that if we focus on the genes that are the same in all three, but different from humans, we have the potential to develop a class of drugs that can target all three diseases."

Trypanosoma brucei is carried by the tsetse fly and causes an estimated 500 000 cases of sleeping sickness every year in sub-Saharan Africa. Trypanosoma cruzi is carried by "kissing bugs" and infects millions of people across Central and South America, killing 50 000 a year.

Leishmania major is carried by phlebotomine sandflies and can cause skin ulcers that leave permanent scars. At any one time some 12 million people from Brazil to Nepal will have it. When it affects internal organs it can cause fatal weight loss and anemia.

One comparative analysis found dozens of genes that all three parasites may have acquired from bacteria. Another found the mechanism that the Chagas disease parasite uses to elude the human immune system.

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