Hookworms have infected humans for thousands of years
Parasitic gut worms, such as hookworm, might aid the development of new treatments for asthma and other allergies, a study in Vietnam suggests.
Infection with hookworm and other parasitic worms is endemic in Vietnam, but rates of asthma and other allergies are low.
British and Vietnamese scientists gave local children treatment to clear their body of worms.
They found this led to an increase in dust mite allergy among the children.
Thanks to improved hygiene practices, parasitic worms have been mostly eradicated among human populations living in developed countries.
However, experts believe that over millions of years of co-evolution worms have found methods to dampen down host immune responses to prolong their own survival inside humans.
This relationship seems to have become so intertwined that without gut worms or other parasites, our immune system can become unbalanced, which, in turn, could contribute to the development of asthma and other allergies.
The latest study was conducted in a rural area of central Vietnam where two in every three children have hookworm and other gut parasite infections, and where allergies are extremely rare.
More than 1,500 schoolchildren aged six to 17 took part.
Some of the children were given repeated tablet treatments to clear their body of gut worms.
The treatment did not produce any conclusive effect on rates of asthma or eczema.
However, those children who received the tablets did have a significantly increased risk of developing allergies to the house-dust mite.
Up to 80% of people with asthma also have allergies to house-dust mites and other environmental allergens.
The researchers said this strongly suggests that gut worms have the potential to tone down human immune responses.
Researcher Dr Carsten Flohr, of the University of Nottingham, said: "The next step is to understand exactly how and when gut parasites programme the human immune system in a way that protects against allergies, and for such studies, follow-up from birth will be essential."
The hope is that the work could aid the development of new treatments which work in the same way as gut parasites, by dampening down or rebalancing the immune system so that the body does not respond to allergens and trigger asthma attacks.
Dr Elaine Vickers, research relations manager at the charity Asthma UK, which funded the research, said: "The prospects of further studies in this area are very exciting as we could see groundbreaking treatments for asthma and other allergies developed as a result."