Abstract
Class II genotype VII Newcastle disease viruses (NDV) are predominant in the Middle East and Asia despite intensive vaccination programs using conventional live and inactivated NDV vaccines. In this study, the protective efficacies of three commercial vaccine regimes involving genotype II NDV, recombinant genotype VII NDV-matched, and an autogenous velogenic NDV genotype VII vaccine were evaluated against challenge with velogenic NDV genotype VII (accession number MG029120). Three vaccination regimes were applied as follows: group-1 received inactivated genotype II, group-2 received inactivated recombinant genotype VII NDV-matched, and group-3 received velogenic inactivated autogenous NDV genotype VII vaccines given on day 7; for the live vaccine doses, each group received the same live genotype II vaccine. The birds in all of the groups were challenged with NDV genotype VII, which was applied on day 28. Protection by the three regimes was evaluated after infection based on mortality rate, clinical signs, gross lesions, virus shedding, seroconversion, and microscopic changes. The results showed that these three vaccination regimes partially protected commercial broilers (73%, 86%, 97%, respectively, vs. 8.6% in non-vaccinated challenged and 0% in non-vaccinated non-challenged birds) against mortality at 10 days post-challenge (dpc). Using inactivated vaccines significantly reduced the virus shedding at the level of the number of shedders and the amount of virus that was shed in all vaccinated groups (G1-3) compared to in the non-vaccinated group (G-4). In conclusion, using closely genotype-matched vaccines (NDV-GVII) provided higher protection than using vaccines that were not closely genotype-matched and non-genotype-matched. The vaccine seeds that were closely related to genotype VII.1.1 provided higher protection against challenge against this genotype since it circulates in the Middle East region. Updating vaccine seeds with recent and closely related isolates provides higher protection.
Highlights
Newcastle disease virus (NDV) is a member of Avulavirinae of the family Paramyxoviridae viruses of the genus Avian orthoavulavirus-1 [1]
ND is caused by virulent strains of Newcastle disease viruses (NDV), which are enzootic in many countries and have been reported worldwide
This study aimed to evaluate the efficacy of the inactivated GII (LaSota) and inactivated recombinant reverse genetic ND vaccine on LaSota backbone-carrying F-HN genes from an Asian NDV-GVII isolate and an autogenous velogenic Newcastle disease virus (VNDV)
Summary
Newcastle disease virus (NDV) is a member of Avulavirinae of the family Paramyxoviridae viruses of the genus Avian orthoavulavirus-1 (formerly designated as the Avian avulavirus-1, commonly known as Avian paramyxovirus) [1]. ND is caused by virulent strains of Newcastle disease viruses (NDV), which are enzootic in many countries and have been reported worldwide. Despite the introduction of vaccines for these viruses for control more than 60 years ago, ND remains one of the most important avian diseases and affects major poultry farms in various countries [2]. NDVs are single stranded, non-segmented, negative sense RNA viruses that encode at least six structural proteins [4]. Many former sub-genotypes did not fulfill the distance (VIIb, VIId, VIIe, VIIj, VIIl), branch support (VIIh, VIIi, VIIk), and/or number of independent isolates (VIIk) criteria. These were merged into a total of three genotype
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