Evaluation of the Efficacy of Inactivated Oil-Emulsion Newcastle Disease Komarov Vaccine against Clinical Disease, Lesions and Immune Response, Following Challenge with Velogenic Newcastle Disease Virus in Laying Chickens
Since the first recognition of Newcastle disease (ND) in Nigeria, it has been observed to be enzootic despite the intensive vaccination policy, leading to significant economic losses in the poultry industry. This study evaluated the ability of inactivated oil-emulsion ND Komarov vaccine to protect laying chickens from challenge with a velogenic ND virus (VNDV). Two hundred and forty pullets were randomly divided into two groups of 120 each viz: vaccinated and unvaccinated groups. The vaccinated group was given ND vaccines. At peak production, 32-weeks of age, vaccinated and unvaccinated laying chickens were sub-divided into four groups of sixty birds each designated; Vaccinated and challenged (VAC); Vaccinated and unchallenged (VAU); Unvaccinated and challenged (UNC); and Unvaccinated and unchallenged (UNU). Groups VAC and UNC were each inoculated intramuscularly with 0.2ml of a VNDV with a median embryo infective dose (EID50) of 106.46 per ml. Groups VAU and UNU were each inoculated with 0.2ml of phosphate buffered saline. Group VAC showed no clinical signs, no clear lesions grossly and mild histopathologic changes. Group UNC showed severe depression, anorexia, whitish-greenish diarrhoea, nervous signs and necrosis of the organs. All infected groups (VAC and UNC) showed significantly higher (P < 0.05) sero-conversion determined by enzyme-linked immunosorbent assay (ELISA) 10 days post-challenge. The inactivated oil-emulsion ND Komarov vaccine not only induced higher immunity, but also conferred long-lasting protection against morbidity, mortality, and severe organ damage in VAC group. This immunization procedure can be recommended for prevention of ND in laying chickens in an endemic environment.
Key words: Newcastle disease, vaccine, laying chickens, immunity.