Vaccination of chickens against Newcastle disease with live and inactivated Newcastle disease virus.

Chickens were vaccinated and revaccinated with inactivated Newcastle disease (ND) vaccines from 2 different sources and also with LaSota strain, live Newcastle disease virus (NDV). Both inactivated vaccines induced higher virus neutralizing (VN) and hemagglutination-inhibition (HI) titers than the LaSota virus. One of the inactivated preparations was found superior to the other by both the VN and HI tests. However, poor protection from apparent virus replication, virus shed, and transmission occurred after challenge with a velogenic NDV strain in those vaccinated with each of the inactivated vaccines. In contrast, LaSota virus, given by the eye drop route, produced excellent protection by the same criteria. In one of the groups of chickens, gross lesions of airsacculitis were seen after vaccination with an inactivated vaccine and subsequent challenge. Revaccination with inactivated vaccines did not enhance the protection of the respiratory tract but did result in an anamnestic serological response (VN and HI). In the post-challenge period, the use of tracheal swabs proved more sensitive as an indicator of virus shed than did cloacal swabs with the velogenic NDV strain used. The practical implications of observations made from the trials are discussed.