Rapid Development of an Effective Newcastle Disease Virus Vaccine Candidate by Attenuation of a Genotype VII Velogenic Isolate Using a Simple Infectious Cloning System.

Nannan Wang,Ding Xiang Liu,Jun Xian Ye,Qian Ru Du,Liang Hai Wen,Mei Huang,Rui Ai Chen,To Sing Fung,Qiong Luo

doi:10.3389/fvets.2020.00648

Abstract

Genotype-matched vaccines provide ideal protection against infection caused by new Newcastle disease virus (NDV) genotypes or variants even in the vaccinated chickens. In this study, we report a protocol for attenuation and rapid development of a velogenic NDV isolate as an effective vaccine candidate, using a simple and reliable infectious cloning platform. Based on DHN3, a genotype VII velogenic NDV isolate, recombinant rDHN3 was rescued by co-transfection of plasmids expressing the genomic RNA, NDV proteins NP, P and L, and the T7 polymerase without using a helper virus. Subsequently, an attenuated strain rDHN3-mF was produced by substitution of residues from amino acids 112 to 117 in the DHN3 F protein with the corresponding sequence from the LaSota strain. Both rDHN3 and rDHN3-mF are genetically stable during propagation in cell culture and chicken embryos. Further characterization through determination of EID50, MDT and clinical assessments confirmed that rDHN3 is velogenic and rDHN3-mF lentogenic. Vaccination of one-week-old SPF chicks with inactivated rDHN3-mF produced much higher anti-DHN3 antibody response and better protection against live DHN3 challenge than did the commercial LaSota vaccine, providing 100% protection and much earlier viral clearance. This attenuated NDV isolate would merit further development into a vaccine product.

Highlights

Newcastle disease (ND) is a highly contagious infectious disease of poultry caused by Newcastle disease virus (NDV)
Sequencing and Phylogenetic Analysis of DHN3, a Local NDV Isolate Classified as Genotype VII
The genome of DHN3 was sequenced from ten cDNA fragments produced by RT-PCR with specific NDV primers (Table 1), in which the primer sequences were conserved in NDV genomes available from GenBank

Summary

Introduction

Newcastle disease (ND) is a highly contagious infectious disease of poultry caused by Newcastle disease virus (NDV). NDV is an enveloped, single-stranded, negative-sense RNA virus, belonging to the Avulavirus genus of the family Paramyxoviridae. NDV attacks multiple organs of chickens, including the respiratory, nervous and digestive systems, with a lethal rate up to 100%. This virus is able to infect over 240 species of birds and spreads by direct contact from the infected to healthy birds [2]. NDV virulence is determined by multiple genetic factors, involving different tissue/cell tropisms and specific immunoresponses induced by viral replication in the infected birds. The ICPI scores > 1.5 are considered velogenic, between 1.5 and 0.7 are mesogenic, and < 0.7 are lentogenic [3]. The mean death time (MDT) scores < 24 hours (h) are considered velogenic, between 24 and 96 h are mesogenic, and >96 h are lentogenic [4]

Methods

Results

Conclusion