Comparative efficacy of three mismatched enterotropic Newcastle disease vaccines against genotype VII challenge in...

Newcastle disease (ND) is a highly contagious disease with the potential to cause massive losses in the global poultry industry. This study evaluated the efficacy of three commercial live ND vaccines based on genotypes I and II (enterotropic) on mortality and viral shedding in specific pathogen-free (SPF) chickens challenged with circulating virulent Newcastle disease virus (vNDV) of genotype VII. Forty one-day-old SPF chickens were randomly divided into four experimental groups (n = 10) and vaccinated (one dose ≥ 10⁶ EID50) with one of three enterotropic ND vaccines (E1, E2, or E3) or received phosphate-buffered saline (PBS) as the control on the 8th day of age. At 28 days of age, the chicks were intramuscularly challenged with genotype VII (GVII) vNDV. Blood samples were collected before the challenge (at 28 days of age) and at 7 and 14 days post-challenge (dpc) to measure serum antibody titers against NDV using the hemagglutination inhibition (HI) test. Cloacal and oropharyngeal swabs were taken on the 3rd, 5th, 7th, and 10th dpc to evaluate viral shedding. The vaccinated groups showed significantly higher antibody titers and protection rates compared with controls (P < 0.05). At 28 days of age, the E2 group had a higher antibody titer compared to E3 (P < 0.05); however, no significant difference was noted between the vaccinated groups at 35 and 42 days of age. All vaccinated chickens showed significantly higher protection in the challenge test compared to the control group; where the E2 group acknowledges the complete protection (70%, 100%, 60%, and 0% for E1, E2, E3, and control, respectively). The E2 group also had the lowest number of shedder birds compared to the E1 and E3 groups (0% vs. 30% and 40%, respectively; P < 0.05). This study shows that some commercially mismatched enterotropic ND vaccines not only provide high levels of protection against genotype VII of vNDV but also effectively control viral shedding in infected chickens.