Up until recently, Crohn’s disease (CD) had been considered a disease specific to industrialized countries. Indeed, developing countries (Africa, Asia and South America) have not been strongly affected by CD up until now; rather, they have a high percentage of infections, especially intestinal parasites. In contrast, counties that have the highest levels of intestinal inflammatory bowel disease (IBD) are those that are least affected by parasitic infections. These observations incited scientists to explore possible links between the two types of disease. In emerging countries and those undergoing epidemiological transition, such as India, i.e. countries in which the standard of living is rising and parasite infections are decreasing, the rate of IBD has drastically increased.

In one Indian study, the authors examined the inverse association between CD and a parasitic worm, the ankylostoma, or hookworm, which infects over 750 million persons throughout the world. By testing the immune system, they showed that most CD patients had never been infected by hookworm, whereas control subjects had a much higher level of infection markers.

That study suggested that the evolution in the standard of living and the decrease in infections (the “hygiene hypothesis”) in industrialized or emerging countries might contribute to an increase in IBD in these countries; it provides additional arguments in favor of a beneficial role for parasites. Moreover, although the idea of infecting CD patients with parasites cannot be envisaged on a large scale, this type of study should trigger us to better elucidate the phenomena by which parasites protect against IBD so as to develop new therapeutic strategies.

Reference:

Kabeerdoss J, Pugazhendhi S, Subramanian V, Binder HJ, Ramakrishna BS. Exposure to hookworms in patients with Crohn's disease: a case-control study. Aliment Pharmacol Ther. 2011 Oct;34(8):923-30.