US Researchers Develop Drug to Treat Schistosomiasis

18 March 2008 -- U.S. researchers have developed a drug that appears to be highly effective in the treatment of schistosomiasis, a parasitic illness that afflicts more than 200 million people, mostly in developing countries.

After malaria, experts say schistosomiasis is the most prevalent infectious disease throughout the tropics, infecting an estimated two hundred million people in Asia, including the Philippines and China, and Latin America, primarily in Brazil, and in the Middle East and Africa.

The experts say another 600 million people are at risk of infection.

The parasitic worm thrives in remote areas in communal water sources, such as lakes and rivers, that are used for bathing and fishing. The parasites infect snails that lay infected eggs. The eggs hatch and the worms are either ingested by humans or penetrate their skin, in what becomes a vicious cycle. When humans excrete into the water new eggs produced by the worms, more snails and people are infected.

If the eggs become lodged in a person's intestinal wall, the disease can cause obstruction of the colon and blood loss. Eggs can also become lodged in the liver and cause a potbelly.

In urinary tract schistosomiasis, the presence of the parasitic eggs causes pain and difficulty urinating in addition to blood loss. People with this kind of schistosomiasis are also at increased risk for bladder cancer.

There is treatment for schistosomiasis. But biochemist David Williams of Illinois State University in Normal, Illinois thinks he and his fellow researchers may have found something better.

"We think it's the Achilles heel in the parasite that we are trying to exploit," said David Williams.

In a paper published in the journal Nature Medicine, Williams and colleagues report the discovery of a compound that appears to be highly effective against the three species of schistosomiasis parasite and in all its stages of infection.

In experiments, the experimental drug significantly reduced the number of worms in mice as well as signs of liver infection.

Williams explains that the parasite needs oxygen to survive. Oxygen use produces oxygen-free radicals that can destroy an organism. But the parasite has an enzyme to protect itself against oxygen-free radicals. Williams says the experimental drug disables the enzyme, causing the parasite to self-destruct.

Williams says the current treatment for schistosomiasis, praziquantel, is effective. But he says it is important for researchers to find other drugs as well.

"In almost every case of every pathogen, every germ, they eventually evolve drug resistance," he said. "So, you think of malaria. You think of chloroquine 20 years ago being a tremendous medication for malaria. It's almost completely worthless now in most places."

Jeffrey Sachs is Director of the Earth Institute at Columbia University in New York. At a recent conference near Washington DC, Sachs weighed in on new drugs to treat tropical illnesses. He said what is needed is a two-pronged approach: trying to stay ahead of drug resistance at the same time remembering the people who are being served.

"Those powerful tools, prevention and treatment, don't reach the poorest of the poor for the very obvious but powerful and tragic reason that the poorest of the poor are too poor to be able to afford just the few dollars that they need to stay alive," said Jeffrey Sachs.

Meanwhile, Illinois State University's Willliams says the experimental drug will have to be reformulated before it is ready for human trials in four to five years.

Source: VOA News

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