COMPARATIVE PATHOLOGICAL STUDY OF EXPERIMENTAL INFECTION OF NEWCASTLE DISEASE VIRUS GENOTYPES VII IN CHICKENS AND DUCKS

Newcastle disease virus (NDV) is a highly contagious virus infects a wide range of avian species including chicken and ducks. The disease can be fatal for many types of them. It was believed that ducks and geese act as natural reservoirs of NDV because of their natural resistance. Recently, NDV isolates were pathogenic for ducks. Therefore, our study aimed to investigate the pathogenicity of highly pathogenic NDV genotype VII in white Ross commercial broiler chickens and Mallard ducks on the basis of clinical, histological observation and immunohistochemistry findings of virus antigen through studying the sequential pathological lesions of both species at 2nd, 5th and 10th dpi. Both species were inoculated via intranasal route by NDV genotype VII (accession number MT887290). Clinical lesions and mortalities were evident mostly in chickens rather than in ducks. Respiratory, digestive and nervous signs were clearly manifested in chickens. Ducks showed low level of mortalities and the nervous signs were the most obvious symptoms. Microscopic findings of chickens showed severe pancreatitis, pneumonia, enteritis as well as pericarditis and brain malacia. Similar findings were noticed in ducks but with lower degree of severity. Brain lesions in ducks included encephalitis and perivascular reaction mostly within the cerebellar tissue. Immunohistochemistry reaction against NDV antigen showed marked immunostaining within epithelial cells, purkinje cells and inflammatory cells mostly the macrophages. The immunohistochemistry reaction was correlated with the pathological findings in both species. In conclusion, the mortality and lesions of NDV in both species were correlated with systemic alterations associated with pancreatitis, pneumonia and encephalopathy. Moreover, the obtained data revealed possible susceptibility of ducks to NDV genotype VII, which might be need forthcoming viral vaccination strategy for ducks against NDV.