Intestinal helminths : a clue explaining the low incidence of inflammatory bowel diseases in Subsaharan Africa ? Potential benefits and hazards of helminth therapy

In their review, the authors state that the very low incidence and prevalence of IBD in sub-Saharan Africa cannot be explained by genetic factors since in Black populations of the USA and UK, the incidence of these diseases is approaching that of the white popu- lations. Beside helminths whose intestinal infestation is frequent in sub- Saharan Africa, other micro-organisms such as atypical mycobac- teria, lactobacilli, etc, might have been reduced in Western popu- lation. This is a new variant of the Hygiene hypothesis. After Rook et al., these micro-organisms were acting as adjuvants for induc- tion of T regulatory cells which, associated with antigen-present- ing cells secrete IL-10 and TGF-b, inhibiting the maturation of CD4 T cells to Th1 and Th2 effector cells, and consequently reduc- ing the occurrence of Th1-mediated diseases like Crohn's disease and Th2-mediated diseases like ulcerative colitis. The effects of intestinal helminths on host immunity have been studied in Ethiopian Jews emigrated to Israël. Thorough studies before and after deworming have demonstrated that chronic helminth infestation provokes a state of chronic immune activa- tion with anergy, reversible after deworming. Administration of ova of Trichuris suis, an helminth non patho- genic in man, has given encouraging results in the treatment o Crohn's disease and ulcerative colitis with a good safety record but long-term trials are needed since the potentially harmful effects of helminths on immunity. (Acta gastroenterol. belg., 2006, 69, 418- 422).