Response of chickens to infection with Newcastle disease virus isolated from a guinea fowl

An isolate of Newcastle disease virus obtained from a guinea fowl was chara cterized as a viscerotropic velogenic strain based upon pathogenicity index studies. Following inoculation of the viral isolate oronasally into 3-week -old chickens, clinical signs appeared after an incubation period of 4-5 da ys and included dullness, depression, dyspnoea, diarrhoea and leg paralysis . The virus caused a mortality of 56% with haemorrhages at the tip of the g lands of the proventriculus and caecal tonsil. Histopathological changes we re prominent in the lymphoid organs, being characterized by depletion, dege neration and necrosis of the lymphoid tissues. The brain was the first orga n affected, with changes being noticed 3 days after infection. Isolation of virus from various organs was more frequent from 5 to 10 days after infect ion, but the virus persisted in some of the organs until 21 days after infe ction. In spite of the high mortality, a good immune response was elicited by the isolate, as was evident from the antibody titre.