Idiopathic polyneuritis in SPF chickens

Paralysis due to peripheral neuritis occurred sporadically in a flock of Rhode Island Red chickens over a period of 8 years and is named idiopathic neuritis (IP). The flock was housed in isolators and free from many common pathogens including all known neurotropic viruses of chickens. The pathology of the nerve lesions, including their ultrastructure, is described and comparisons made with the lesions of Marek's disease and experimental allergic neuritis in chickens. Demyelination with invasion of nerve fibres with lymphocytes and macrophages occurs in all three diseases but there are differences in lesion distribution and intensity of cellular infiltration. The closest similarity is between the lesions of IP and the B-type lesions of Marek's disease. Attempts to isolate a cytopathic virus and to transmit the disease by inoculation failed to demonstrate an infectious causal agent. An autoimmune response to normal nerve is suggested as the most likely aetiology amongst several alternatives. The heritability of IP is not established, but the disease has not been detected in a light Sussex flock maintained under similar conditions.