A little dirt is good for you

In the studies of hygiene hypothesis,researchers are concluding that organisms like the millions of bacteria,viruses and especially worms that enter the body along with dirt spur the development of a healthy immune system. Several continuing studies suggest that worms may help to redirect an immune system that has gone awry and resulted in autoimmune disorders,allergies and asthma.

These studies,along with epidemiological observations,seem to explain why immune system disorders like multiple sclerosis,Type 1 diabetes,inflammatory bowel disease,asthma and allergies have risen significantly in the developed countries.

Training the immune system

What a child is doing when he puts things in his mouth is allowing his immune response to explore his environment, Mary Ruebush,a microbiology and immunology instructor,wrote in her new book,Why Dirt Is Good (Kaplan).

Leading researcher Dr Joel V. Weinstock,the director of gastroenterology and hepatology at Tufts Medical Center in Boston,said in an interview that the immune system at birth is like an unprogrammed computer. It needs instruction. He said public health measures like cleaning up contaminated water and food have saved the lives of many children,but they also eliminated exposure to organisms that are probably good for us.

Children raised in an ultraclean environment, he added,are not being exposed to organisms that help them develop appropriate immune regulatory circuits.

Studies he has conducted with Dr David Elliott,a gastroenterologist and immunologist at the University of Iowa,indicate that intestinal worms,which have been all but eliminated in developed countries,are likely to be the biggest player in regulating the immune system to respond appropriately,Dr Elliott said.

Most worms are harmless,especially in well-nourished people,Dr Weinstock said. There are few diseases that people get from worms, he said. Humans have adapted to the presence of most of them.

Worms for health

In studies in mice,Dr Weinstock and Dr Elliott have used worms to both prevent and reverse autoimmune disease. Dr Elliott said in Argentina,researchers found that patients with multiple sclerosis who were infected with the human whipworm had milder cases and fewer flare-ups of their disease over a period of four and a half years. At the University of Wisconsin,Madison,Dr John Fleming,a neurologist,is testing whether the pig whipworm can temper the effects of multiple sclerosis.

In Gambia,the eradication of worms in some villages led to childrens having increased skin reactions to allergens,Dr Elliott said. And pig whipworms,which reside only briefly in the human intestinal tract,have had good effects in treating the inflammatory bowel diseases,Crohns disease and ulcerative colitis,he said.

How may worms affect the immune system? Dr Elliott explained that immune regulation is now known to be more complex than scientists thought when the hygiene hypothesis was first introduced by a British epidemiologist,David P Strachan,in 1989. Dr Strachan noted an association between large family size and reduced rates of asthma and allergies.

Dr Elliott said: Dirtiness comes with a price. But cleanliness comes with a price,too. If we properly understand how organisms in the environment protect us,maybe we can give a vaccine or mimic their effects with some innocuous stimulus.

Wash in moderation

Dr Ruebush,the Why Dirt Is Good author,correctly points out that bacteria are everywhere: on us,in us and all around us. Most of these micro-organisms cause no problem,and many,like the ones that normally live in the digestive tract and produce life-sustaining nutrients,are essential to good health. The typical human probably harbours some 90 trillion microbes, she wrote. The very fact that you have so many microbes of so many different kinds is what keeps you healthy most of the time. Dr Ruebush deplores the current fetish for the hundreds of antibacterial products. Plain soap and water are all that are needed to become clean.

I certainly recommend washing your hands after using the bathroom,before eating,after changing a diaper,before and after handling food, and whenever they are visibly soiled,she wrote. When no running water is available,she suggests an alcohol-based hand sanitiser.

Dr Weinstock goes a step further. Children should be allowed to

go barefoot and play in the dirt and not have to wash their hands before eating, he said. He and Dr Elliott pointed out that children who

grow up on farms and are frequently exposed to worms and other organisms are much less likely to develop allergies and autoimmune diseases. Also helpful,he said,is to let kids have two dogs and a cat,which will expose them to intestinal worms that can promote a healthy immune system.