Equine grass sickness is associated with major abnormalities in the ultrastructure of skeletal neuromuscular junctions

Background Equine grass sickness (EGS) is a frequently fatal multisystem neuropathy of equids. The aetiology is unknown; proposed causes include toxicoinfection with Clostridium botulinum and a mycotoxicosis. The effect of EGS on the organisation and structural integrity of the skeletal neuromuscular junction (NMJ), the target of botulinum neurotoxins (BoNTs), is unknown. Objectives To compare the organisation and structural integrity of skeletal NMJs from EGS horses, control horses and one horse with a presumptive diagnosis of botulism. Study design Blinded, retrospective case control. Methods NMJs in samples of diaphragm or intercostal muscle from six EGS horses, three control horses and one equine botulism case were compared using electron microscopy, morphometry and confocal light microscopy. Results A significantly higher percentage of EGS NMJs had abnormal morphology (EGS 72.2%, 95% CI 55.6–84.4; Controls 6.9%, 1.7–23.8; OR 35.1, 8.47–244.8; p