Investigating an Outbreak of Newcastle Disease among Vaccinated and Unvaccinated Poultry Chicken

The burden of Newcastle disease may continue to increase due to non-adherence to poultry vaccination policies among some commercial poultry farmers. The purpose of this study was to investigate a suspected outbreak of Newcastle disease (ND) among clusters of vaccinated and unvaccinated poultry chickens. Poultry Farm (Farm Z) with 600 capacity deep litter pen (A and B) and capacity of 300 birds each procured two sets of poultry at 21 days of life from two separate farms (X and Y mixed layer & broiler) on the 2nd of May 2024. Pen A: was stocked with Layers of chicken from farm (X) poultry chicken has prior vaccination against ND as of 21st of May 2024 (N=242), Pen B were stocked with broilers chicken (N₂=216) from farm Y with no history of vaccination against Newcastle diseases as at 21st of May, 2024. On the 5th of May, 2024, 142 poultry chickens were procured comprising 58 layers and 84 broilers from farm (Y) with no vaccination history against Newcastle disease to make up a poultry flock size of 300 in each pen A (N=58; 242), Pen B (N₂=84;216). The risk of NCD amongst Vaccinated poultry was 3% and 45% in unvaccinated poultry. The relative risk of NCD in the vaccinated poultry population was 7%, and vaccine effectiveness against ND in vaccinated Poultry was 97%. 142(100%) samples from moribund and dead poultry chicken were positive for Newcastle disease by indirect ELISA test of these 8(6%) were from vaccinated poultry and 134(94%) were unvaccinated. Practices such as mixing of vaccinated and unvaccinated poultry flocks may be inimical to the growth of the poultry subsector. Vaccination regimens against ND in poultry should not be compromised as a means to reduce the cost of production by procuring cheap unvaccinated apparently healthy flocks