Page last updated at 17:51 GMT, Thursday, 29 January 2009

Are worms vital to human health?

By Diane Roberts
BBC News health producer

The hookworm may help treat people with asthma

Could the humble worm hold the key to wiping out allergies and a whole lot of disorders of the immune system?

Researchers in Nottingham are investigating whether giving hook worms to asthma sufferers can cure their condition.

Another group in the US is trying a pig worm on patients with ulcerative colitis or inflammation of the colon and bowel.

And scientists in Cambridge have proved that giving an extract of the tropical worm which causes bilharzia to mice can stop them developing type 1 diabetes.

The theory behind all this is that worms and other organisms, through our evolutionary history, developed a role in driving our immune systems.

Professor Danny Altman, professor of immunity at Imperial College, said: "There is compelling evidence that something in our immune systems has changed since our ancestors, in fact has changed since our great grandparents.

"But what we're not saying is that this mechanism is the only reason we're seeing the rise in allergies."

Worms and immunity

The scientists, who have all written articles for the journal Immunology, said the key compound in question is found in worms, in mud and in the tiny organisms (flora) in our guts.

Professor Graham Rook, an expert of medical microbiology at University College London, said: "What we think is that the immune system has become dependent on signals from certain organisms."

He said a fascinating recent study had illustrated this.

Bacteria were introduced to a group of amoebae. The amoebae did not like the bacteria and tried to kill them - but could not.

And five years later neither organism could live without the other.

The amoebae had deleted certain genes in their own immune systems and the bacteria had done the same so they could coexist peacefully.

As a result, the amoebae no longer had a complete genome unless the bacteria were present.

Professor Rook said: "It now looks more and more likely that the development of our regulatory immune system depends on molecules that are encoded not in the genome of the human but in the genome of some other organism we lived with throughout history."

Girl sneezing
Hay fever and asthma are both disorders of the immune system
He said the hygiene hypothesis theory that our over clean environment was causing allergies was being constantly disproved.

And there were now good reasons to think that a whole range of autoimmune disorders and even some cases of depression were a result of our diminished exposure to these bugs.

And it is not just humans; animals too can benefit.

Professor Rook described an experiment carried out by a veterinary company on dogs suffering from eczema.

The dogs had been forced to eat human food and drink bottled water by their owners.

A bacterium found in the mud surrounding cowsheds was given to them and the eczema disappeared.

He said instead of focusing on the hygiene hypothesis scientists would be better advised to examine this more recent theory - the "old friends" hypothesis.

Some worms 'good'

Professor Jan Bradley, a parasitologist from the University of Nottingham, said some worms could live in the human body for 15 to 20 years.

She said: "The question I've been asking is how does a worm modify the host so it can survive that long?

"If you dissect any free-living organism it has worms. It's full of them, in its blood, guts, everywhere.

"It is only in the last 50 years in Britain that humans have been free of worms. If, for instance, you look at the faeces of the Vikings you can find evidence of them having worms."

Professor Bradley said in the past we would have eaten our own sewage through contaminated water systems or spreading it on crops.

And even getting bitten a lot by insects would help to keep a healthy amount of worms in our system.

"We have evolved to have worms. Worms can have adverse consequences but maybe there's a positive side which we can exploit in new therapies for allergies."


Professor Anne Cooke, professor of immunology at the University of Cambridge, talked about the rise in type 1 diabetes cases.

She said type 1 had both genetic and environmental causes and it had been known for some time that certain infections could block the development of the condition.

"In the UK the number of cases is increasing by 4% a year, that's faster than can be accounted for by genetic changes."

Hay fever
Inflammatory bowel disease
Neuroinflammatory diseases like Alzheimers
Clogged arteries
Some forms of depression
Some forms of cancer

She has looked at the tropical worm, Schistosoma mansoni, which carries a parasite which causes the illness bilharzia.

The worm can remain in the human body for up to 40 years.

During that time male and females mate and excrete eggs which come out in the faeces.

They hatch and infect water snails which eventually may reinfect the human.

So it is likely that there has been an adaptation between the parasite and its human host.

Professor Cooke said it had been shown that an infection with schistosoma mansoni could prevent the development of type 1 diabetes in mice.

But she said we were a long way off a treatment for humans.

"As we work out the genes that govern diseases, who an individual is is down to the organisms their ancestors were exposed to.

"Infection shapes the genetic endowment of the population.

"It will allow you to identify pathways of disease and allow you to modify them with small molecules, not the whole worm."

"Before I would even consider treating a child with type 1 diabetes I would have to be sure it was safe and understand the mechanisms underlying it.

"We are talking about using fractions not the whole parasite."

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