European outbreaks of atypical myopathy in grazing equids (2006-2009): spatiotemporal distribution, history and clinical features.
Authors: van Galen G, Marcillaud Pitel C, Saegerman C, Patarin F, Amory H, Baily J D, Cassart D, Gerber V, Hahn C, Harris P, Keen J A, Kirschvink N, Lefere L, McGorum B, Muller J M V, Picavet M T J E, Piercy R J, Roscher K, Serteyn D, Unger L, van der Kolk J H, van Loon G, Verwilghen D, Westermann C M, Votion D M
Journal: Equine veterinary journal
Summary
# Atypical Myopathy in European Grazing Equids: Epidemiological Patterns and Clinical Presentation (2006–2009) Between 2006 and 2009, a multinational European surveillance network identified 354 confirmed or highly probable cases of atypical myopathy (AM) amongst 600 suspected animals, with major outbreaks clustering in autumn 2006 and 2009 across Belgium, France and Germany. The investigation characterised the spatiotemporal distribution, clinical presentation and management circumstances surrounding AM development, revealing that affected equids spent more than six hours daily on pastures containing or bordered by trees, with an estimated incubation period of up to four days preceding clinical signs. Beyond the traditionally recognised presentation in adult horses, this outbreak series documented AM affecting donkeys, zebras and geriatric equines for the first time, whilst expanding the known clinical phenotype to include gastrointestinal impaction, diarrhoea, penile prolapse, buccal ulceration and renal dysfunction alongside rhabdomyolysis; however, survival remained poor at 26% overall. Although breed predisposition, body condition and pasture management varied geographically, the core clinical signs and high mortality were consistent across affected countries, suggesting a common aetiological agent with environmental triggers relating to tree-associated exposure. These findings provide valuable epidemiological scaffolding for prevention and diagnosis, yet the causal mechanisms warrant investigation through prospective case-control studies to establish which specific management and environmental factors genuinely modulate disease risk versus those merely correlating with affected populations.
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Practical Takeaways
- •Grazing horses should be monitored closely during autumn months (particularly September-November) in tree-bordered or tree-containing pastures, especially in continental Europe; consider reduced grazing time or alternative management during high-risk periods
- •AM presents with variable clinical signs including muscle weakness, gastrointestinal signs, and renal dysfunction; clinicians should maintain high suspicion in autumn-affected grazing horses regardless of age or breed
- •Environmental management focused on pasture characteristics (proximity to trees) and grazing duration may help reduce AM incidence; further case-control studies needed to confirm causal relationships
Key Findings
- •354 confirmed or highly probable AM cases identified from 600 suspected cases across Europe (2006-2009)
- •Largest outbreaks occurred in autumn 2006 and 2009 in Belgium, France and Germany with 26% overall survival rate
- •For the first time, donkeys, zebras and older horses were documented as affected, expanding previous understanding of susceptibility
- •Affected horses spent >6 hours/day on pastures containing or surrounded by trees with estimated latency period up to 4 days