Researchers Pin Down Genome of Parasitic Worms
RENEE MONTAGNE, Host:
If you're not familiar with filarial nematodes, count yourself lucky. They are threadlike parasitic worms and they can cause painful and disfiguring swelling of the legs. It's a condition known as elephantiasis.
Now, scientists have taken a potentially important step in fighting that parasite. They've sequenced the genome of one of the worms. They're hoping the genetic information will lead to new treatments for the disease.
NPR's Joe Palca reports.
JOE PALCA: Infection with a filarial nematode is not a minor problem.
ELODIE GHEDIN: It's thought that about a billion people are at risk for this parasite.
PALCA: Yes, molecular biologist Elodie Ghedin said a billion people. Ghedin is at the University of Pittsburg School of Medicine. The parasite is transmitted by mosquito and it turns up all over the world - Africa, Asia, South America, even a handful of cases in the United States. Ghedin says you can be infected and not even know it.
GHEDIN: A lot of the people that are infected may not have disease symptoms, necessarily. They may be asymptomatic, but they're carrying the parasite.
PALCA: We'll come back to that point a little later in this story. But now, here's what happens to people who get infected and do get symptoms: The worms get into their lymph nodes and block them up.
GHEDIN: And if they're blocked, you get massive swelling and they can have - the skin can then have the consistency of elephant skin and elephant-shaped limbs and, hence, the name elephantiasis.
PALCA: A decade ago, scientists including Ghendin began a project to unravel the complete genetic sequence of the parasite. In the current issue of the journal, Science, she and 70 co-authors report they have just about succeeded.
GHEDIN: We haven't been able to assemble the genome into individual chromosomes, so it's still in little pieces. But we're able to do a lot of the analyses even on these pieces.
PALCA: For people who work on parasitic diseases, the genome sequence is a breakthrough.
MICHAEL GOTTLIEB: This is the tool that advances the field.
PALCA: Michael Gootlieb is with the Foundation for the National Institutes of Health.
GOTTLIEB: The immediacy is not that within the next couple of years we're going to have new drugs or a vaccine, but it provides the sort of very basic biology - the evolution of these organisms.
PALCA: Some people have already begun to spend new strategies for fighting the parasite based on the new sequence information. Steven Williams has been working on the filarial genome project from the start. He's now on the faculty of Smith College and at the Task Force for Child Survival and Development. He says when the parasite infects someone, the first thing it does is shed its outer skin or molt.
STEVEN WILLIAMS: Anything that blocks the molt is going to prevent development of the parasite, prevent development of the disease. Something that targets the molt is unlikely to have side effects in the human because we don't molt.
PALCA: Williams has been sifting through the new DNA sequence information looking for genes that control molting.
Now, you remember I mentioned that most people who are infected with filarial nematodes don't get sick? Elodie Ghedin says, somehow a worm knows how to slow down a human's immune system.
GHEDIN: It's accepted by the body. There's no immune response that's really mounted against it.
PALCA: Ghedin says that's interesting because maybe the worm genes that can turn off our immune system could become new drugs for preventing immune rejection of organ transplants. Poetic justice of a parasite that caused so much misery could lead to drugs that improve people's lives.
Joe Palca, NPR News, Washington.
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