Case Study: Polioencephalomalacia in Merino hoggets
On a farm near Heathcote in central Victoria, in a mob of 400 Merino wether hoggets grazing lush pasture, four were found dead and three others showed nervous signs. Of the latter, one was recumbent with opisthotonus (Figure 1), one was standing and stargazing (Figure 2), and one was up and down and adopting unusual postures. All had a pupillary light reflex, none had a menace reflex and all behaved as though blind. Vaccination history was uncertain.
Polioencephalomalacia was confirmed histologically based on the laminar pattern of oedema and necrosis in the deep gray matter of the sulci and gyri of the cerebral cortex. There was no evidence of focal symmetrical encephalomalacia, the brain lesion of enterotoxaemia and the main differential diagnosis, thus urgent vaccination was not warranted.
- Tristan Jubb, Bendigo Sheep Vets