Animal exposure over the life-course and risk of multiple sclerosis: A case-control study within two cohorts of US women

Background: Whether animal exposure and specifically the timing of such exposure alters multiple sclerosis (MS) risk is unclear. We examined whether animal exposure was associated with MS risk, and whether risk differed by the participants age.

Methods: We conducted a case-control study within the Nurses' Health Study ((NHS)/NHSII cohorts). Overall, 151 women with MS and 235 controls, matched by age and study cohort, completed an animal exposure history questionnaire. Animal exposure pre-MS onset was assessed as 'any' exposure, then by the participants age, and animal family. Conditional logistic regression was used to estimate relative MS risks, adjusted (adj.RR) for potential confounders.

Results: 'Any' animal exposure was reported by 136 (90.1%) MS cases compared to 200 (85.1%) matched controls, with dog exposure being the most common [120 (79.5%) cases vs. 170 (72.3%) controls]. There was no association between 'any' animal exposure and MS risk (adj.RR:1.52;95%CI:0.76-3.04). However, both 'any' animal and specifically dog exposure at ages 10-14 years were associated with an increased MS risk (adj.RR:1.67;95%CI:1.05-2.66 and 1.76;95%CI:1.12-2.78, respectively).

Conclusion: Animal exposure, and specifically dog exposure, in early adolescence was associated with an increased risk of MS. Further work is needed to confirm this finding.