Antibody and titer virus shedding in the chicken vaccinated against inactivated local strain of Newcastle disease virus (NDV) genotype VII

Abstract

Newcastle disease is a very contagious disease in chickens and one of the most important diseases of poultry in the world. This study aimed to compare the effect on immune response and virus shedding in vaccinated chickens of the new inactivated vaccine of Newcastle disease virus (NDV) and commercial vaccine LaSota. The local subtype of NDV Genotype VIId (isolate 12234/10) was chosen as inactivated vaccine candidate and three different adjuvants were used which includes Oil-emulsion Complete Freund’s, Oil-emulsion Squalene-based, and aluminium hydroxide gel (Alum). Ten different groups of chicken consists of ten each, were vaccinated with and without adjuvant of the inactivated vaccine via intramuscular and subcutaneous, respectively. As a comparison, a group of chicken was vaccinated with commercial vaccine and control group was not vaccinated. Then, all of the chickens were challenged with NDV Genotype VIIh (isolate 7979/01) two weeks after vaccination. Blood sera of the chickens were taken weekly for haemaglutination-inhibition (HI) test starting from prior to vaccination. Virus shedding of the chickens were calculated based on the virus isolation done within two weeks after challenge. With 100% survival rate and highest mean HI titre of log2 7.8, the inactivated vaccine with adjuvant Oil-emulsion Complete Freund’s surpassed the LaSota and the virus shedding also reduced significantly. Alum-adjuvanted inactivated vaccine gave most impressive results as LaSota with all chickens survived at log2 6 of antibody titer and zero virus shedding. Whereas, without adjuvant, the chicken HI antibody titre is below log2 4 after vaccination and only 20-30% were survived. Based on the post-mortem findings on the survived chicken from each vaccinated group, their internal organs appeared normal and no sign of haemorrhage or pathognomonic signs of Newcastle disease (ND). Conclusively, vaccinated chicken are effectively protected from morbidity and mortality against virulent genotype VII challenge with the addition of adjuvant into inactivated local strain of NDV genotype VII vaccine. Thus, the development of inactivated local NDV genotype VII vaccine is a promising candidate to control the current ND endemic in Malaysia.