Avian Encephalomyelitis in Embryos and Abnormal Chicks on the Day of Hatching : Neurohistopathological Observations

Neurohistopathological investigation was carried out on 224 individuals which consisted of 52 not pipping embryos, 49 pipping embryos, 17 culled chicks, and 106 weak chicks and which had been randomly collected on the day of hatching. Forty-three individuals had histological lesions characteristic of avian encephalomyelitis. The percentage incidence of this disease was 11.5% in the not pipping embryos, 20.4% in the pipping embryos, 35.3% in the culled chicks and 19.8% in the weak chicks. The lesions were composed of central chromatolysis or tigrolysis (axonal reaction) of large motor nerve cells in the brain and spinal cord. The reactive changes were negligible. In addition, the same degenerative alterations as seen in the large motor nerve cells were observed in ganglion cells of the spinal ganglion. These changes were considered to be equivalent to the lesions of the brain and spinal cord. The results obtained give a morphological proof of the egg transmission of avian encephalomyelitis, which has been presumed to be possible since the first reports on this disease.