Polymorphisms affecting the gE and gI proteins partly contribute to the virulence of a newly-emergent highly virulent Chinese pseudorabies virus.

An outbreak of a highly virulent pseudorabies virus strain, ZJ01, occurred in PRV-vaccinated pigs in China in 2011. In this study, ZJ01 caused fatal diseases, while the Chinese prototypic PRV strain LA caused mild respiratory disorders. Full-genome sequencing results indicate the two viruses can be classified into two sub-clusters that distinct from traditional European and US strains. To examine the potential role of the gE and gI proteins in ZJ01 virulence, we generated several recombinant viruses. In two chimeric viruses (rZJ01-LA/gEI and rLA-ZJ01/gEI), the gE and gI genes were swapped using corresponding genes from ZJ01 and LA. rZJ01-LA/gEI and the parental virus rZJ01 retained high virulence in piglets, although the survival time for rZJ01-LA/gEI infected piglets was obviously prolonged. In contrast, rLA-ZJ01/gEI exhibited higher virulence than its parental virus rLA. We conclude that changes in gE and gI proteins partly contribute to the enhanced virulence of ZJ01 strain.

Comparative pathogenicity and immunogenicity of triple and double gene-deletion pseudorabies virus vaccine candidates.

Pseudorabies (PR) outbreaks have re-emerged in many pig farms with vaccination coverage in China, which suggests that current vaccine strains provide poor protection against novel, epidemic strains. In this study, based on the highly virulent PRV ZJ01 variant, a PR virus (PRV) thymidine kinase (TK)/gE/gI deleted strain-rZJ01ΔTK/gE/gI-was generated, which showed similar growth features in vitro compared to the parent strain PRV ZJ01 and its gE/gI deleted strain rZJ01ΔgE/gI. The results of a piglet experiment (with 10 piglets each group) showed that the rZJ01ΔTK/gE/gI vaccine generated similar levels of neutralizing antibodies against ZJ01 compared to the rZJ01ΔgE/gI vaccine (p>0.05). However, rZJ01ΔgE/gI inoculation resulted in slight inflammatory cell infiltrations, hemorrhages, and congestion in the brain and lungs. After a ZJ01 challenge, all animals in the rZJ01ΔTK/gE/gI- and rZJ01ΔgE/gI-vaccinated groups survived without exhibiting any clinical symptoms, whereas all non-vaccinated control animals died within 7days post-challenge. Furthermore, microscopic lesions and virus loads in the brains and lungs in the two vaccinated groups were significantly lower than those in the control group. Meanwhile, the virus levels in the brains of piglets in the rZJ01ΔTK/gE/gI group were significantly lower than those in the rZJ01ΔgE/gI group. These results indicate that the triple gene-deleted PRV rZJ01ΔTK/gE/gI strain has lower pathogenicity and higher protective efficacy against variant PRV challenge compared with the double gene-deleted PRV rZJ01ΔgE/gI strain. Together, all these data indicate that the PRV rZJ01ΔTK/gE/gI strain should be an ideal vaccine candidate for the prevention of PR in China.

Emergence of highly virulent pseudorabies virus in southern China.

Pseudorabies has been controlled efficiently in China for many years by vaccination. However, it suddenly broke out in many pig farms in 2012-2013 in southern China. In this study, a systematic investigation that included virus isolation, genetic and pathological studies, and immunogenicity analysis was carried out with the aim of understanding the pathogenetic and antigenic features of novel isolates of pseudorabies virus (PRV). Of 38 tissue samples collected from pigs with clinical signs of pseudorabies on 13 farms in 4 provinces in southern China in 2012-2013, 29 showed wild-type PRV infection by polymerase chain reaction. Sequence analysis of 5 isolates from the 4 provinces showed that they belonged to a relatively independent cluster that shared 2 insertions of a single amino acid in the gE gene and 1 insertion of 7 amino acids in the gC gene. In experiments, isolate ZJ01 caused death in 100% of pigs that were either 14 or 80 days old. The serum antibodies to the commercial PRV vaccines had significantly lower neutralizing activity against the ZJ01 isolate than against the vaccine strains. The antigenic relatedness between ZJ01 and the vaccine strains was 0.378 to 0.455. These findings indicated that a novel, highly virulent PRV strain with antigenic variance had spread widely in southern China.

La pseudorage a été maitrisée de manière efficace en Chine pendant plusieurs années grâce à la vaccination. Toutefois, en 2012­2013 des poussées de cas sont apparues soudainement dans des fermes porcines dans le sud de la Chine. Dans la présente enquête, l'isolement viral, des études génétiques et pathologiques, et des analyses d'immunogénicité furent effectués avec l'objectif de comprendre les caractéristiques pathogénétiques et antigéniques des nouveaux isolats du virus de la pseudorage (VPR). À partir de 38 échantillons de tissu prélevés en 2012­2013 chez des porcs avec des signes cliniques de pseudorage provenant de 13 fermes dans quatre provinces du sud de la Chine, 29 se sont révélés positifs par réaction d'amplification en chaîne par la polymérase pour une infection par une souche sauvage du VPR. L'analyse de séquence de cinq isolats provenant des quatre provinces montrait qu'ils appartenaient à un regroupement relativement indépendant qui partageait deux insertions d'un acide aminé unique dans le gène gE et une insertion de sept acides aminés dans le gène gC. Lors d'expériences, l'isolat ZJ01 causait la mort chez 100 % des porcs qui étaient âgés de 14 ou 80 jours. Les anticorps sériques envers les vaccins VPR commerciaux avaient une activité neutralisante significativement moindre contre l'isolat ZJ01 que contre les souches vaccinales. La parenté antigénique entre ZJ01 et les souches vaccinales variait de 0,378 à 0,455. Ces trouvailles indiquent qu'une souche nouvelle et hautement virulente du VPR avec une variance antigénique s'est répandue largement dans le sud de la Chine.(Traduit par Docteur Serge Messier).

A novel inactivated gE/gI deleted pseudorabies virus (PRV) vaccine completely protects pigs from an emerged variant PRV challenge.

A highly virulent and antigenic variant of pseudorabies virus (PRV) broke out in China at the end of 2011 and caused great economic loss in the pig industry. In this study, an infectious bacterial artificial chromosome (BAC) clone containing the full-length genome of the emerged variant PRV ZJ01 strain was generated. The BAC-derived viruses, vZJ01-GFPΔgE/gI (gE/gI deleted strain, and exhibiting green autofluorescence), vZJ01ΔgE/gI (gE/gI deleted strain), and vZJ01gE/gI-R (gE/gI revertant strain), showed similar in vitro growth to their parent strain. In pigs, inactivated vZJ01ΔgE/gI vaccine generated significantly high levels of neutralizing antibodies against ZJ01 compared with Bartha-K61 live vaccine (p<0.05). After fatal ZJ01 challenge, all five animals in the inactivated vZJ01ΔgE/gI vaccine group survived without exhibiting any clinical sings, but two of five animals exhibited central nervous signs in the Bartha-K61 group. Meanwhile, all the non-vaccinated control animals died at 7 days post-challenge. This indicates that the inactivated vZJ01ΔgE/gI vaccine is a promising vaccine candidate for controlling the variant strains of PRV now circulating in China.