HELMINTHS AND IBD EPIDEMIOLOGY

There are a wealth of data that support an immunoregulatory role for helminth infection in animal models and the human host.^1–3 Recently, this concept has been utilised therapeutically for the treatment of patients with inflammatory bowel disease (IBD). Specifically, Summers and colleagues⁴ report the results of their open study of live Trichuris suis ova therapy in 29 patients with Crohn’s disease (CD) in this issue of Gut(see page 87).⁴ Treatment with T suis appears safe and effective in the short term, even with concurrent immunosuppressive therapy. Extension of this concept into the “hygiene hypothesis”⁵ may seem increasingly attractive in terms of an explanation for some epidemiological observations in patients with IBD, in particular the north-south gradient for IBD prevalence in both North America and Europe, and the lack of IBD in developing nations.^6–8 However, some of these epidemiological observations should be viewed with caution. Studies that find a north-south gradient are limited to determining incidence rates and do not attempt to tackle the more difficult task of finding epidemiological reasons behind the gradient. In addition, the stringent “rules” that are now being applied to replication of genetic association and linkage studies have not been applied to all epidemiological studies in IBD. Recent data on paediatric IBD and twin studies would support an increasingly important role for environmental factors over genetics. Specifically, paediatric IBD has increased in frequency in the recent past (1990–2001), is becoming increasingly multi-ethnic, and less often familial, and repeat twin studies from Scandinavia using a new (younger) cohort show reduced concordance rates for CD.^9–11 Multiple environmental factors, including pathogen exposure, diet, …