The Price of Cleanliness
Colin F. Burrows, BVetMed, PhD, MRCVS, Diplomate ACVIM
Two small human studies, 1 of 54 patients with ulcerative colitis and 1 of 29 patients with Crohn's disease, evaluated the effect of orally ingested ova of Trichuris suis (porcine whipworm). The hypothesis was that infection with parasitic worms is protective because the infections downregulate the immune response. For patients with ulcerative colitis, 43.3% that ingested ova experienced disease improvement compared with 16.7% of patients receiving placebo. By the 12th week, 75.9% of patients with Crohn's disease had a decrease in symptoms and by the 24th week, 79.3% showed improvement with 72.4% in remission. Pig parasites were used instead of the human parasite T. trichiura, because T. suis colonizes the gut for only a short time.
COMMENTARY: The concept that some diseases of the 20th and 21st centuries result from changes in lifestyle or the environment has been postulated for a long time. People in "developed" countries live in a cleaner, more sanitary environment with minimal exposure to parasites and food- or water-borne infectious disease than their third-world counterparts. They are also more likely to be vaccinated against common diseases. However, as is pointed out in this review, disorders like inflammatory bowel disease are much more common in developed than in undeveloped countries. We drink purified water; eat purified, processed, or inspected foods; and breathe filtered conditioned air. Our immune systems therefore do not receive the same degree of exposure to antigens as those of persons who live in less-sterile environments. My mother, who grew up in rural England in the early 20th century, used to say that children should eat a peck of dirt as they grew up. There was a firm belief among these rural folk that getting dirty was healthy. As I grew up and learned about the sciences of food hygiene and infectious disease, I naturally scoffed at this belief. The fact, however, that porcine intestinal parasites positively modulate 2 related diseases that are believed to be associated with an imperfect immune system gives much food for thought. Modern food hygiene has saved countless lives, and there should be no desire to step back in time to when we ate uninspected, fly-blown meat or drank water straight from potentially polluted rivers and streams. But these studies do raise a number of interesting questions. Have we perhaps gone too far down the sterile and clean road? Are our immune systems being insufficiently stimulated or stimulated in the wrong way? We have a long way to go before treatment of inflammatory bowel disease with Trichuris extract becomes routine, but the prospect of what lies ahead is fascinating.
Pig whipworm ova found active in Crohn's disease and ulcerative colitis. Harby K. DIGESTIVE DISEASE WEEK 2004:Abstracts 580 and 644.