People lived closer to the soil in the past, without indoor plumbing and with direct exposure to animals. The result was near universal colonization with helminths, which are complex wormlike animals that inhabit the gastrointestinal tracts of mammals. Like the many bacteria also found in the gut, some helminths can cause disease in a host animal but many are relatively harmless and, in fact, are important regulators of the immune system.
According to Dr. J. Weinstock , a gastroenterologist at Tufts University, " helminths exert a powerful effect on immunity in the host, primarily by inducing the regulatory arm of the immune system, which is important in reigning in the effector ' fight and kill ' arm of the immune system." The regulatory arm hones and shapes the immune response to bacteria, viruses, and parasites, quelling the effects of the effector arm so as to prevent needless tissue damage by turning against the host.
Diseases such as IBD, asthma, rheumatoid arthritis, and multiple sclerosis remain uncommon in less-developed parts of the world where helminthic colonization is still widespread.
Interestingly, petrified human stool many thousands of years old has been found to contain helminth eggs, and autopsies of mummies have found traces of helminths. In fact, the frozen iceman Otzi, found in the northern Alps in 1991 where he had lain in a glacier since 3300 B.C., had T. trichiura in his gut.
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Ann. Rheum. Dis. 2008;67:518-23