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.” ...
[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.
--Elizabeth Svoboda, NYT, on an old-school antihistamine