Effect of post-infection vaccination on immune status of Newcastle disease-infected chicken

Abstract

This study investigated the response of chicks infected with velogenic Newcastle disease virus (NDV) to Newcastle disease vaccine - NDV-I2. A total of 90 day-old cockerel chicks were used for this study. At three weeks of age, the chicks were randomly separated into
two equal groups of 45 chicks designated A and B. After separation, Group A chicks were vaccinated with NDV-I2 vaccine intraocularly, while Group B chicks were not vaccinated. At six weeks of age, Groups A and B chicks were further randomly separated into sub groups A1, A2, A3 and B1, B2, B3 of 15 chicks each respectively. After separation, chicks in subgroups A2, A3, B2, and B3 were exposed to chicks infected with NDV. Upon manifestation of clinical infections, chicks in subgroups A2 and B2 were revaccinated with NDV-I2 vaccine, while subgroups A3 and B3 were not vaccinated. Percentage morbidity was 42.86, 64.29, 100 and 92.86 % for subgroups A2, A3, B2 and B3 respectively, while percentage mortality was 14.29, 50, 100 and 71.43 % in subgroups A2, A3, B2 and B3 respectively. This study showed that vaccination of previously vaccinated chicks during Newcastle disease outbreak protects the chicks and reduces both morbidity and mortality significantly.

Keywords: Cockerels, Newcastle disease, Vaccination, Revaccination, Geometric mean titre, Morbidity, Mortality