The Protective Efficacy of Recombinant Herpesvirus of Turkey (rHVT-ND-IBD) Vaccine Against Challenge with Velogenic Newcastle Disease Virus Genotype VII.1.1

Abstract

<title>Abstract</title> Newcastle disease virus (NDV) outbreaks occurred in several vaccinated and non-vaccinated poultry farms all over the world causing severe economic losses despite extensive vaccination. Class II genotype VII.1.1 NDV are predominant in Middle East and Asia, despite intensive vaccination regimes. In this study the protective efficacy of recombinant herpesvirus of turkey (rHVT-ND-IBD) expressing F protein of genotype VII with either live and /or inactivated ND conventional genotype II vaccines was evaluated in broilers against challenge with velogenic Newcastle disease virus (VNDV) genotype VII.1.1 (Chicken/ USC/Egypt /2015 with accession number MG029120) strain. Four vaccination regimes were used: live ND vaccine (V4 and LaSota) alone on day 1 &amp;14, respectively, (G4) or either with rHVT-ND-IBD vector vaccine on day 1 (G3) or inactivated NDV vaccine (G1) or rHVT-ND-IBD vector and inactivated NDV vaccines on day 1 &amp;7, respectively. In addition, non-vaccinated birds (G5). All groups were challenged on days 21 &amp; 28. The assessment of protection was based on seroconversion, clinical protection, mean lesion scores (MLS) of histopathological changes and tracheal virus shedding after challenge with velogenic NDV genotype VII.1.1. The results showed that all vaccinated groups (G1, G2, G3 &amp; G4) were clinically protected in compared to severe clinical signs with 85% mortality rate of non-vaccinated group (G5) when challenged on day 21. Whereas, after challenge on day 28 the clinical signs were varied from mild (G2 &amp; G3), moderate (G1) and severe (G4) <italic>vs</italic> very severe respiratory, neurological and gastrointestinal disorders (G5). In addition, the mortality rates were 12.5%, 0%, 0% and 50% in G1, G2, G3 and G4, respectively, <italic>vs</italic> 87.5% in G5. Moreover, the tracheal virus shedding in G2 &amp; G3 were significantly (p ≤ 0.01) reduced when compared to the G1, G4 &amp; G5. The MLS were significantly (p ≤ 0.01) decreased in G2 and G3 when compared to other groups. It was concluded from this study that a complete clinical protection against challenge with genotype VII.I.I NDV was revealed in broilers vaccinated with live NDV genotype II and both the inactivated NDV genotype II and bivalent rHVT-IBD-ND vaccines. Upon that the combination of bivalent rHVT-IBD-ND with live and inactivated ND vaccines in broilers is recommended to obtain optimum clinical protection against genotype VII.1.1, especially in endemic countries.