The disappearance of intestinal parasites from humans in developed countries may be responsible for the upsurge in many diseases including Celiac Disease, Crohn's, ulcerative colitis, asthma and hay fever. A parasite's survival relies on its ability to interfere with the host's immune response. The mechanisms employed to do this are similar to those required by a person to regulate against the so-called autoimmune disorders, diseases in which the system turns on itself. The investigators suspect that when parasites are excluded from the environment, some individuals become sufficiently self-reactive to develop an autoimmune disease. American researchers have successfully treated patients with Crohn's and ulcerative colitis using a pig whipworm (Trichuris suis). The investigators have undertaken a similar preliminary study using a human hookworm in Crohn's patients.