Comparison of protection and viral shedding following vaccination with Newcastle disease virus strains of different genotypes used in vaccine formulation

Newcastle disease (ND) is a devastating disease and cause high t mortality and morbidity in poultry and nonpoultry avian species worldwide. An intensive vaccination program against ND is a routine practice in Pakistan like other developing countries, but still frequent outbreaks have been recorded in the field. In this study, vaccines prepared from ND viruses corresponding to four different genotypes were compared, to determine if the phylogenetic distance between vaccine and challenge strain influences the protection induced the amount of challenge virus shed. In the experiment, 1-day-old pathogen-free Hubbard chicks were divided into five groups and all groups except control were received live LaSota vaccine. The chicks were re-vaccinated at day 5 and were given oil-adjuvanted inactivated vaccines prepared from one of four different inactivated NDV strains including SFR-55 (genotype-VIIi), Chicken-12 (XIIIb), Mukteswar (III), and LaSota (II), and control group was treated with PBS only. Pre- and post-challenge serum was collected from all groups and tested for antibody against NDV using hemagglutination inhibition (HI) assay. After challenged with virulent SFR-55, the birds were examined daily for morbidity and mortality and were monitored at selected intervals for viral shedding. All the vaccines induced high immune response, and all the groups except the control induced >84% protection against vNDV challenge. The vaccine genetically and antigeneically similar with challenge NDV strain reduced oral shedding significantly as compared to mismatched strains. From the present study, it was concluded that genotype-matched vaccine has potential to result in better protection by limiting the viral shedding.