Atypical Myopathy: Epidemiology and Aetiopathogenesis

Since 2006, more than 1000 European horses have been suspected of suffering from atypical myopathy (AM) (Votion 2004), a highly fatal myopathic syndrome that may affect horses kept on pastures. For unknown reasons, this last decade, outbreaks of AM have occured more frequently in Europe (van Galen et al. 2012a). Epidemiological investigations have highlighted the contribution of environmental factors as triggering factors of outbreaks (Votion et al. 2007, 2009; van Galen et al. 2012a). With the contribution of specific laboratory research, epidemiological studies have raised some aetiological hypotheses and ruled out others. The hypothesis of toxic products, such as ionophores, herbicides, weed killers, nitrates and nitrites has been discarded. Also, nutritional myopathy is not believed to be the cause of AM even if the administration of antioxidants was the only medical support that appeared to be beneficial for a positive outcome (van Galen et al. 2012b). The seasonality of AM (outbreaks are mainly reported in autumn) and its link with climatic conditions that are favourable to fungal growth have raised the hypothesis of the action of a mycotoxin, but none of the toxins suspected were known to induce a rhabdomyolysis syndrome (Brandt et al. 1997). Toxic plants were not consistently present in the pastures of affected horses (Hosieet al. 1986; Brandt et al. 1997; Votion et al. 2007). However, the possible role of maple leaves contaminated with an endophyte in the aetiology of AM has been suggested (van der Kolk et al. 2010) but scientific evidence was lacking. In the same way, the role of Clostridium sordellii was suspected (Unger-Torroledo et al. 2010). […]