When parasites are practical

Studies: Often health hazards, the creatures may become a vital tool in the fight against autoimmune disorders.

Medicine & Science

August 30, 2004|By David Kohn | David Kohn,SUN STAFF

Schistosoma is not a pleasant creature. A parasitic worm about a centimeter long, it begins life by infecting snails and eventually emigrates to whatever body of water its host inhabits.

When the creature crosses paths with a human, it grabs hold and burrows under the skin, making its way to the intestines or bladder, where it can live for more than a decade, gorging on blood cells.

The worm, which infects 200 million people globally, can cause a variety of problems, from fever to liver damage.

But nasty as it is, Schistosoma could turn out to be a tiny Florence Nightingale.

By introducing the parasite and others like it into patients, scientists now think they can help treat a variety of autoimmune disorders - including allergies, asthma, rheumatoid arthritis, multiple sclerosis, diabetes and some intestinal diseases.

"It's becoming quite fashionable now," says Cambridge University immunobiologist Anne Cooke, who is studying the worms' effect on diabetes.

Scientists have had success using worm eggs to treat Inflammatory Bowel disease, a painful, sometimes fatal, disorder of the digestive tract.

"We saw significant benefit," says University of Iowa gastroenterologist Joel Weinstock, who led the studies. He gave about 120 patients several doses of 2,500 eggs from a worm called Trichuris suis, which normally infects pigs. The parasites live for only a few weeks in humans, and seem to cause no symptoms or damage.

Half of Weinstock's subjects were so happy with the results that they maintained the worm regimen even after the studies ended.

Raymond Fiedler was among this group. Before the experiment, the 66-year-old retired schoolteacher from Clinton, Iowa, was in bad shape - his colon so inflamed that doctors thought it would need surgery.

`It's been wonderful'

But after the worm treatment, the inflammation disappeared, as did his persistent diarrhea. Fiedler's disease is now in remission.

"It's been wonderful for me," he said. He had no qualms about gulping the worm eggs. Dissolved in a glass of Gatorade, they were invisible to the naked eye and had no taste, he said.

Weinstock is now working with drug companies to standardize the worm treatment, and hopes to begin large-scale human trials in Europe this year.

Apparently the pigworm treatment works by calming the immune system, which attacks the body's own intestines. Researchers say this "immunomodulation" is the key to the parasites' promise.

Known scientifically as helminths, these creatures exist all over the world. About 50 afflict humans and some cause serious health problems, including blindness, anemia and intestinal damage.

To survive, the creatures have developed ingenious ways of selectively tweaking the human immune system. In some cases, they can survive for decades.

By understanding how the helminths subtly dampen our immune response, researchers hope to develop treatments for other diseases in which the immune system attacks the body's own tissues. These include asthma, rheumatoid arthritis and multiple sclerosis.

Researchers say a worm-based approach could neutralize overly aggressive immune cells, providing help for disorders that currently have no cure.

Current treatments rely heavily on harsh immunosuppressive drugs, which typically don't cure the underlying disease and often impair the immune system, leaving patients vulnerable to other illnesses.

Scientists aren't sure how the parasites work their immunomodulatory magic. Many researchers think the worms activate specialized cells called Regulatory T cells, which put a leash on the immune system's attack dogs.

Helminths may have helped humans avoid some diseases over the ages.

Researchers say it's no coincidence that rates of autoimmune disorders have risen rapidly in the Western World while parasitic infections have dropped sharply.

This theory, known as the Hygiene Hypothesis, argues that until the past century, an overwhelming majority of humans likely were infected with these parasites. In the face of this widespread infection, the human immune system calibrated itself to the worms' presence. With improvements in sanitation, refrigeration and modern medicine, the worms - along with a range of bacterial and viral infections - all but disappeared from the developed world.

Proponents of the idea say that in the absence of these worms, the human immune system is more likely to get confused and attack its own body.

"When you take away the parasites, the immune system has a tendency to overreact," says Rick Maizel, an immunologist at the University of Edinburgh in Scotland.

Parasites' secrets

Most scientists agree that worms themselves won't make good medicine. Even if researchers could render the creatures harmless, worm-based treatments would be a tough sell to the typical medical consumer. But once the parasites' secrets are unraveled, researchers say they can develop drugs to mimic helminthian tricks.

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