People with asthma and hay fever are being deliberately infected with hookworms to test whether the blood-sucking parasites can control the allergic reactions that cause the conditions.

If the study by British scientists is successful, it would open a new approach to controlling allergic and auto-immune conditions. Hookworm infestations could be induced under medical supervision to reduce symptoms, or the worms could help the development of new drugs. It has been understood since the 1970s that people with hookworms, an intestinal parasite, rarely have allergic conditions such as asthma and hay fever.

There is also evidence that they are protected against multiple sclerosis and Crohn’s disease. Both are caused by the body’s immune system, which overreacts to cause excessive inflammation or to attack healthy tissue.

Parasites such as hookworms can survive only by avoiding detection and destruction by the immune system, and so produce proteins to damp it down. Infections of about ten worms can be tolerated by otherwise healthy people.

Professor David Pritchard of the University of Nottingham, who is leading the research, told the festival yesterday that groups of hayfever sufferers had been given hookworms: “Many of the people who were given a placebo have now requested worms. And the people with worms, many of them have decided to keep them for the next hay fever season.”

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