Are worms vital to human health?


Recent research projects in Nottingham, the US and Cambridge (focusing on hook worms and asthma, pig worms and ulcerative colitis and the tropical worm which causes the parasitic disease, bilharzia and type 1 diabetes) all suggest that worms and other organisms, through our evolutionary history, have developed a role in driving our immune systems.

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 our gut flora.

Professor Graham Rook, a medical microbiologist at University College London, said that they thought 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....
The hygiene hypothesis theory that our overclean environment is causing allergies is being constantly disproved. There are now good reasons to think that a whole range of autoimmune disorders and even some cases of depression are a result of our diminished exposure to these bugs.

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

‘If you dissect any free-living organism’ she said, ‘it has worms. It's full of them, in its blood, in its guts, everywhere. ‘It is only in the last 50 years in Britain that humans have been free of worms. In the past we would have eaten our own sewage through contaminated water systems or spreading it on crops. 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 that 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 (of 4% a year), far faster than can be accounted for by any genetic change.
She has looked at the tropical worm, Schistosoma mansoni, which carries a parasite that 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 still a long way off a treatment for humans.

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First Published in March 2009

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