The worm against allergies

New York Times, July 1st 2008 (Link):

While carrying out field work in Papua New Guinea in the late 1980s, Dr. Pritchard, an immunologist-biologist at the University of Nottingham (foto to the left), noticed that Papuans infected with the Necator americanus hookworm (foto to the right), a parasite that lives in the human gut, did not suffer much from an assortment of autoimmune-related illnesses, including hay fever and asthma.

His explanation for this phenomenon is that "the allergic response evolved to help expel parasites" and that "the worms have found a way of switching off the immune system in order to survive...".

To test his theory, and to see whether he can translate it into therapeutic pay dirt, Dr. Pritchard infected himself with hookworms: 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. “The itch when they cross through your skin is indescribable,” he said. “My wife was a bit nervous about the whole thing.”

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.