Experimental vermeersiekte (Geigeria ornativa O. Hoffm. poisoning) in sheep. II: Histological and ultrastructural lesions.

The histological and ultrastructural lesions of sheep (n = 5) with experimentally-induced vermeersiekte (Geigeria ornativa O. Hoffm. poisoning) were studied. Histological changes in the muscles of the skeletal system, diaphragm and oesophagus comprised hypertrophy and vacuolation of myofibres. In 2 sheep, foci of myocardial degeneration and necrosis were present. No microscopical changes were detected in the central nervous system and in peripheral nerves of the oesophagus and the hind limb. Ultrastructural alterations in the myocardium, semimembranosus muscle and oesophagus were characterised by concurrent myofibrillar degeneration and mitochondrial swelling. The earliest myofibrillar change appeared to be loss of the thick filaments followed by fragmentation and disorganisation and eventually by lysis of central myofibrils. Focal thickening, fragmentation and clumping of Z-band material and dissociation and fragmentation of intercalated discs accompanied the myofibrillar and mitochondrial alterations.