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Friday, 2 November, 2001, 00:52 GMT
Worm infestation 'beats asthma'
The hookworm uses sharp "teeth" to attach itself to the gut
The humble hookworm may have a secret which could help scientists investigating treatments for asthma.

Infestations with these parasites are commonplace in countries such as Ethiopia.

The worms migrate through the body via the lungs to the gut, then attach themselves to the lining to drink blood.

Researchers found that Ethiopians who showed signs of having had hookworm infestation were far less likely to report wheezing - a key symptom of asthma.

It seems possible that the hookworm, and perhaps some other types of gut parasite, are able to suppress the kind of immune reactions which are oversensitive in asthmatics.

They may block the allergy response which causes asthma

Dr Sarah Scrivener, Nottingham City Hospital
However, although the study may offer clues for scientists studying asthma, this could never be considered a reasonable trade-off for people infected with the parasite.

In susceptible children hookworms cause intellectual, cognitive and growth retardation, as well as intrauterine growth retardation, prematurity and low birth weight among newborns born to infected mothers.

A quarter infected

The results of the study, conducted principally at the University of Nottingham and Jimma University in Ethiopia, are published in the medical journal The Lancet.

They examined just over 200 Ethiopians with asthma, and compared them with almost 400 non-asthmatic controls.

Faecal samples were examined for signs of parasitic infection.

In total, hookworm was present in 24% of everyone tested.

They found that people with hookworm infestation were only half as likely to suffer from wheeze - and there seemed to be some relationship between the level of infection and the risk.

The project concluded that there was an increased risk of wheeze in urban areas covered by the project partly due to the protective effect of hookworm infestation, and partly due to increased dust-mite allergen exposure in a town setting.

The reason behind this, however, remains at least partly a mystery to the teams.

The journey of the worm into the human host is circuitous - from the feet, the parasite makes its way up via blood vessels to the lung, where it can move up into the throat, and then get swallowed down into the digestive system.

Here it uses sharp "teeth" to attach itself firmly to the gut wall.

Eradication programme

One suggestion is that, while passing through the lung, the worm can digest a body chemical which primes the immune system for action.

Dr Sarah Scrivener, from Nottingham University said: "They may block the allergy response which causes asthma.

"Some kinds of hookworm secrete proteins which can damp down the immune response."

The finding has implications in two areas - firstly, for investigators looking for new drugs which may help people control asthma, and secondly, for the worm-eradication programmes being undertaken in many parts of the world.

Hookworm infestation is certainly a contributor to ill-health in many parts of the globe.

The Gates Foundation - founded by Microsoft's Bill Gates and his wife Melinda - has donated $18m to the Sabin Vaccine Foundation in an effort to produce a hookworm vaccine.

However, researchers have warned that eradication of worms may mean an upsurge in asthma, particularly in urban areas.

Rates of asthma in developed countries are far higher than those in developing countries, and scientists are still trying to work out all the reasons why.

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