In 2004, David Pritchard applied a dressing to his arm that was crawling with pin-size hookworm larvae, like maggots on the surface of meat. He left the wrap on for several days to make sure that the squirming freeloaders would infiltrate his system.
David Pritchard, an immunologist-biologist at the University of Nottingham, infected himself with hookworms.
David Pritchard, shown writing in 1990 with his research team on Karkar Island, Papua New Guinea.
“The itch when they cross through your skin is indescribable,” he said. “My wife was a bit nervous about the whole thing.”
Dr. Pritchard, an immunologist-biologist at the University of Nottingham, is no masochist. His self-infection was in the interest of science.
While carrying out field work in Papua New Guinea in the late 1980s, he noticed that Papuans infected with the Necator americanus hookworm, a parasite that lives in the human gut, did not suffer much from an assortment of autoimmune-related illnesses, including hay fever and asthma. Over the years, Dr. Pritchard has developed a theory to explain the phenomenon.
“The allergic response evolved to help expel parasites, and we think the worms have found a way of switching off the immune system in order to survive,” he said. “That’s why infected people have fewer allergic symptoms.”
To test his theory, and to see whether he can translate it into therapeutic pay dirt, Dr. Pritchard is recruiting clinical trial participants willing to be infected with 10 hookworms each in hopes of banishing their allergies and asthma.
Never one to sidestep his own experimental cures, Dr. Pritchard initially used himself as a subject to secure approval from the National Health Services ethics committee in Britain.
In the tropics, where it is common, hookworm kills 65,000 people a year and afflicts hundreds of thousands with anemia. In low numbers in adults in a controlled experiment, Dr. Pritchard said, the worms have not caused problems.
His interest in the immunology of parasite infection stretches back to 1977. Intrigued by anecdotal reports from third world countries that parasites warded off allergy symptoms, he completed his Ph.D. thesis at the University of Birmingham on that topic.
Afterward, he was an allergist at a pharmaceutical company, but the work bored him, and he returned to academia at Nottingham in 1981, investigating the ways parasitic worms suppressed rodents’ immune systems.
“At that time,” he said, “I realized the definitive work had to be carried out in humans. So I began to make inquiries about possible tropical venues for this research.”
In the late 1980s, the Wellcome Trust issued a grant, and Dr. Pritchard and his Nottingham team set up camp on Karkar Island, Papua New Guinea.
“We didn’t speak the language, and we were sparsely equipped,” he recalled. “But we established a rapport with the people. We gave them worm tablets and would ask them politely, in pidgin English, to collect their fecal matter in buckets for us.”
Hookworm infiltrates a victim’s system when the larvae, hatched from eggs in infected people’s excrement, penetrate the skin, often through the soles of the feet. From there, they enter the bloodstream, travel to the heart and lungs, and are swallowed when they reach the pharynx. They mature into adults once they reach the small intestine, where they can subsist for years by latching onto the intestinal wall and siphoning off blood. After sieving the fecal samples to extract hookworms eliminated when the worm treatment pill was given, the team reached an intriguing conclusion: Villagers with the highest levels of allergy-related antibodies in their blood had the smallest and least fertile parasites, indicating that these antibodies conferred a degree of protection against parasite infection.
And the hookworms seemed equipped to retaliate. After colonizing a digestive tract, the host often showed signs of a blunted immune response, leading Dr. Pritchard to suspect that the worms were reducing the potency of the body’s defenses to make their environment more hospitable.
“Sitting in the jungle for long periods gives you time to think,” he noted. “And this led to the idea that worm burdens of tolerable intensity could be beneficial under some circumstances.”
He began considering a left-field possibility. What if he could round up allergy sufferers, give them worms and see whether their wheezing and watery eyes disappeared?
Nearly 20 years later, his musing began to come to fruition. After Dr. Pritchard’s self-infection experiment, the National Health Services ethics committee let him conduct a study in 2006 with 30 participants, 15 of whom received 10 hookworms each. Tests showed that after six weeks, the T-cells of the 15 worm recipients began to produce lower levels of chemicals associated with inflammatory response, indicating that their immune systems were more suppressed than those of the 15 placebo recipients. Despite playing host to small numbers of parasites, worm recipients reported little discomfort.
Trial participants raved about their allergy symptoms disappearing. Word about the study soon appeared online among chronic allergy sufferers, and a Yahoo group on “helminthic therapy” sprung up.
“Many of the people who were given a placebo have requested worms, and many of the people with worms have elected to keep them,” Dr. Pritchard said.
Now he is recruiting patients for a larger-scale trial of the therapy, and he said he hoped to publish his results within the next year.
Some allergy sufferers cannot wait. The moderator of the Yahoo group, Jasper Lawrence, a Silicon Valley entrepreneur, has started a clinic in Mexico, to offer the unproven therapy (a basic worm “inoculation” costs $3,900).
Mind Control By Parasites