Association between exposure to farm animals and pets and risk of Multiple Sclerosis

https://doi.org/10.1016/j.msard.2016.08.015Get rights and content

Highlights

  • Inconsistent evidence exists regarding the association between exposure to pets and/or other animals and MS risk.

  • Our group recently showed that farming and exposure to livestock increased the risk of demyelination.

  • In this study, farming, exposure to livestock or specific farm animals were not associated with MS.

Abstract

Purpose

There exists inconsistent evidence regarding animals including pets as risk factors for the development of Multiple Sclerosis (MS). We investigated the association between farm animals and pets as possible environmental factors in MS development.

Methods

Population based case-control study with 136 clinically definite MS cases and 272 controls randomly chosen from the community matched on sex and age. Data was collected from both questionnaire and a lifetime calendar detailing residence, occupation and pet/animal exposure over the course of participant's lives.

Results

Exposure to farming, livestock, specific farm animals and remoteness of residence showed no significant association with MS risk. Exposure to cats prior to disease onset was associated with a greater risk of MS (Adjusted Odds Ratio 2.46 (1.17–5.18)) but without a clear dose-response (test for trend, p=0.76).

Conclusions

In contrast to other literature, farming and exposure to farm animals were not associated with MS. While we identified an association between cat exposure and MS, there was no dose-response relationship, and previous studies showed inconsistent results, leaving us to conclude that there is no strong evidence that exposure to cats is associated with MS.

Introduction

Multiple Sclerosis (MS) is a complex disease of the central nervous system, and aetiological factors continue to be uncovered (Pakpoor and Ramagopalan, 2014). Contagious viral illnesses of pets, such as canine distemper, may potentially be associated with an increased risk of MS. However, immune modulation as a result of exposure to pets could also have a beneficial effect, in line with the “hygiene hypothesis”, which proposes that early life infections may down-regulate allergic and autoimmune disorders (Bach, 2001). Inconsistent evidence exists regarding the association between exposure to pets and/or other animals and MS risk (Ghadirian et al., 2001, Bansil et al., 1997, Alonso et al., 2011), but our group recently identified a positive association between farming and exposure to livestock and risk of central nervous system demyelination (Valery et al., 2013). In a population based case-control study in Tasmania, we examined whether farming, and exposure to pets and farm animals prior to the onset of MS was associated with MS risk.

Section snippets

Study participants

The population is described in greater detail elsewhere (van der Mei et al., 2003, Ponsonby et al., 2005). People with MS under the age of 60 years were recruited in the state of Tasmania through the use of advertising, information evenings and letters from neurologists. In total, 169 subjects volunteered to participate, while 136 cases were included in the final sample. Thirty (17.8%) did not meet the study protocol with regard to the diagnosis of MS, one person refused a neurological

Results

Overall, 68% of participants were female, and the mean time since diagnosis of the cases was 9.4 years (Table 1). Table 2 shows the association between exposure to various animals and MS. In relation to farm-related variables, no associations were found for being a farmer (only two controls were farmers and no cases), living on a farm, exposure to specific farm animals (cows, sheep, horses, pigs, poultry, goats, sheep dogs, native animals or ferrets), or a variable that combined the individual

Discussion

This population-based case-control study investigated whether farming and exposure to various pets or farm animals influenced the risk of MS. No associations were observed for farming, exposure to farm animals or remoteness of residence. We observed that people with MS were more likely to have had exposure to cats before diagnosis (OR 2.46 (1.17–5.18)), but there was no dose-response association with duration of exposure to cats, leaving it doubtful whether this was a true association. If there

Conflict of interest

There are no relevant conflicts of interest to declare.

Funding

This project was supported with funding from the National Health and Medical Research Council (NHMRC) of Australia (ID 106928), the Australian Rotary Health Research Fund, and MS Australia. IvdM is supported by an ARC Future Fellowship.

Acknowledgements

We thank the participants, Trish Groom and Jane Pittaway for conducting the environmental interviews, Ceri Flowers for the genetic fieldwork, Natasha Newton for administrative support and data entry, Sue Sawbridge and Tim Albion for the development and management of the database, Andrea Polanowski for the genotyping, the Tasmanian Multiple Sclerosis Society for assisting with the recruitment of volunteers, and Trevor Kilpatrick, H. Butzkueven, A. Hughes, B. Drulovis, and S. Siejka who were

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    Furthermore, it has been proposed that exposure to animals (kept as pets) may influence the risk of MS. For instance, exposure to animals who are prone to demyelinating diseases (e.g. German Shepherds) might be associated with an increased risk of MS (Clemmons, 1992; Lincoln et al., 2008). Despite previous efforts, studies have shown conflicting results (Cook and Dowling, 1977; Jotkowitz, 1977; Cook et al., 1978; Read et al., 1982; Norman et al., 1983; Anderson et al., 1984; Flodin et al., 1988; Operskalski et al., 1989; Landtblom et al., 1993; Bansil et al., 1997; Ghadirian et al., 2001; Hernán et al., 2001; Alonso et al., 2011; Conradi et al., 2011; Gustavsen et al., 2014; Siejka et al., 2016). Several studies have shown that people living with MS were more often exposed to animals in the years before the onset compared to healthy controls or controls with other neurological diseases (Cook and Dowling, 1977; Jotkowitz, 1977; Cook et al., 1978; Flodin et al., 1988; Landtblom et al., 1993; Bansil et al., 1997; Hernán et al., 2001; Siejka et al., 2016).

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