Investigations into an acute paralysis syndrome in broiler chickens

The acute paralysis syndrome (APS) under investigation at the University of New England (UNE) and the Elizabeth Macarthur Agricultural Institute (EMAI), is characterised by paralysis causing sternal recumbency and marked flaccidity of the head and neck in broiler chickens, leading to death, from 24 - 40+ days of age, with typically low flock mortality. Disease is more common in warmer periods of the year, and has not been observed in other than broiler chickens. Affected birds do not typically display gross lesions, rather associated histopathological lesions include perivascular cuffing of mononuclear cells, perivascular oedema, and endothelial hypertrophy in the cerebrum and spinal cord, and additionally in the spinal cord, wallerian degeneration. Diagnostics performed in the field do not support the involvement of a range of potential causative agents including Clostridium botulinum, avian influenza (Al), and Newcastle disease (ND). Marek's disease virus (MDV) has been detected in affected flocks, however the incidence of APS has not fallen in response to HVT vaccination.