He did not realise it during his visit in the 1980s, but Professor Pritchard was taking the first step on a journey that was to lead to the discovery of a treatment that might change the lives of millions of people with auto-immune illnesses, such as hay fever and multiple sclerosis.

Earlier this year in Nottingham, Prof Pritchard received a shipment of Necator americanus for a worldwide first trial using hookworms as a treatment for auto-immune diseases, in which the immune system goes into overdrive.

Initial results presented yesterday to the British Association for the Advancement of Science’s conference in York, show that the hookworms appear to "down regulate" the immune system. Trials with hay fever sufferers confirmed that the hookworms stimulate the body to produce white blood cells called regulatory T-cells, that dampen down the immune response.

Volunteers are being recruited for a second trial with asthma sufferers and there are plans for studies on Crohn’s disease and multiple sclerosis. Prof Pritchard, who has infected his body with 50 hookworms, said yesterday that asthma tended to be concentrated in the developed world.

"If you superimpose a map of where hookworms are found, you will see that asthma and hookworms seem to be mutually exclusive," he said. "Similarly, Crohn’s disease seems to be a disease of the developed world."

Necator americanus is estimated to infect one billion people in tropical and subtropical countries. It attaches itself to the intestinal wall, sucking blood, and can remain in the body for five years.

Prof Pritchard said that after the hookworms migrated to his gut he felt "a dull ache under the rib cage". It was decided the correct dosage was ten – any more resulted in discomfort; any fewer and the immune-suppressing effects were not strong enough. The worms cannot reproduce inside the body and are eradicated with tablets.