USA – In underdeveloped countries, a high percentage of the population is infected with worms.  However, it has puzzled researchers how the parasites protect their host from Crohn’s disease and other inflammatory bowel diseases that occur much more frequently in industrialized countries.

American doctors have now found that the worms affect the composition of the intestinal flora.  As experiments with mice, germs analyzed from infected humans before and after a worm treatment showed the parasites change the germ counts of two groups of intestinal bacteria. The health-promoting displacement of the germ spectrum based on the fact that the worm infection stimulates the immune system to produce specific messengers, according to the researchers who published their work in the journal Science.

“We were able to show that worms can reduce inflammation in the intestine by promoting the growth of protective intestinal bacteria, causing the spread of pro-inflammatory bacteria is inhibited,” explained Ken Cadwell and his colleagues at the New York University School of Medicine.

Their findings are consistent with the hygiene hypothesis.  After frequent contact with environmental pathogens, the immune system is stimulated from rare to excessive immune reactions and allergic diseases. Often asymptomatic, intestinal infection caused by parasitic worms had positive side effect: The infected patients are less likely to suffer from inflammatory bowel disease.

Mice study

The researchers began their investigations with mice whose intestinal mucosa showed similar damage due to a defective gene (Nod2), as they also occur in Crohn’s disease. These animals had Bacteroides vulgatus that can cause inflammation, a greater proportion of total intestinal flora than in normal mice.  Then the scientists infected the animals with Trichuris muris, related with the whipworm type of nematodes. Thereby, the damaged intestinal mucosa returned to normal gradually, which enhances the immune messengers interleukin-4 and interleukin-produced.

Thirteen further experiments confirmed that these interleukins ensured a reduction in Bacteroides vulgatus germ counts.  At the same time increased the proliferation of another group of intestinal bacteria, the Clostridia, which are anti-inflammatory. Similar results delivered infections with the parasite worm Heligmosomoides polygyrus.

Human study

Finally, the researchers moved to human subjects.  They were analyzed of intestinal bacteria of two populations in Malaysia.  Members of the people of the Orang Asli, who lived far from major cities, were 96% infected with worms.  For residents of the capital Kuala Lumpur, there were only 5 percent.  In fact, people with intestinal parasites had lower bacterial counts on Bacteroides bacteria.  And after a drug treatment of helminths infection of Bacteroides showed increased on the intestinal flora, while the Clostridienzahl decreased. These are indications that certain variants of the gene Nod2 have increased susceptibility to Crohn’s disease. Perhaps only those patients benefit from a worm infection, but not those with normal Nod2 gene, the authors write.  However, the new results could help to develop new treatment strategies, at least for those affected.