PATHOMORPHOLOGICAL OBSERVATIONS IN BROILE R-CHICKENS WITH DIFFERENT IMMUNE STATUS, EXPERIMENTALLY INFECTED BY VELOGENIC NEWCASTLE-DISEASE VIRUS

Broiler chickens, immunized at the age of four weeks against ND, and s howing different serological responses were challenged with the HERTS 33/56 velogenic strain of NDV three weeks later. 24% of the chickens d ied 5 to 9 days later (Fig 1), 33% showed clinical disease but 43% sur vived and showed no clinical symptoms throughout the observation perio d of the two week experiment. Clinical symptoms (Table 1) and gross-pa thological alterations (Table 2) characteristic for ND were more signi ficant in the dead and affected but survived chickens than in the symp tomless animals, in which macroscopic alterations were observed only s poradically. The histopathological examinations revealed lymphocytic e ncephalomyelitis accompanied by exudative alterations of circulatory d isturbances were observed in the central and peripheral nervous system of dead and/as well as affected and two weeks later exsanguinated chi ckens. Circulatory disturbances, exudative and degenerative alteration s were found in the viscera and signs of lymphocyte degeneration and i nflammation in the lymphoid organs (Figs 2 to 13). Proliferative lymph ocytic inflammation was observed in the central and peripheral nervous system of sick but survived and symptomless chickens. The viscera sho wed also proliferative multiples focal lympho-histiocytic infiltration and hyperplasia in the lymphoid organs (Tables 3, 4 and 5). Morbidity as well as mortality and character of the pathological features showe d a direct correlation with the degree of seroconversion observed at t he time of challenge (Table 6).