BRAIN-LESIONS IN YOUNG BROILER-CHICKENS NATURALLY INFECTED WITH A MESOGENIC STRAIN OF NEWCASTLE-DISEASE VIRUS

Thirty-nine 4- to 5-week-old broiler chickens from an outbreak of Newc astle disease (ND) in Japan were examined pathologically. The causativ e agent was identified as a mesogenic strain of ND virus. Predominant gross lesions included haemorrhage in the lungs, congestion of the tra chea, splenomegaly, atrophy of the thymus and bursa of Fabricius, and whitish discolouration of the brain. Microscopically, there was mild h aemorrhagic pneumonia, catarrhal tracheitis, lymphoid necrosis in the spleen, thymus, bursa of Fabricius and caecum and diffuse non-suppurat ive encephalitis. Lesions associated with encephalitis were characteri zed by multifocal perivascular cuffing, malacia, demyelination and pro liferative vasculitis. Malacic lesions occurred in the hyperstriatum, neostriatum, subleptomeningeal and periventricular regions of the cere brum, whereas demyelination was seen mainly in the brain stem. The mor phological changes that occurred in the brain in these cases were dist inctive and the lesions in the lymphoid tissues were related to concur rent infection with infectious bursal disease virus.