1. Introduction
Pseudorabies (PR) disease, or Aujeszky’s disease, caused by pseudorabies virus (PRV, a member of the family Herpesviridae , subfamilyAlphaherpescirinae , and genus Varicellocirus ), is one of the most important viral diseases of pigs and results in gravely economic harm to swine industry in many countries (Pomeranz et al., 2005, Muller et al., 2011). Infected pigs display a range of symptoms, including the neurological disorders and high mortality in newborn piglets, severe respiratory illness in adult pigs and reproductive failure in sows (Gu et al., 2018). The first description of PR was made in America as early as 1813, and the first recorded case of China was in 1948, with following epidemic in pigs in the late 1980s (Ketusing et al., 2014). Due to the use of the gE-negative vaccine strain Bartha-K61 imported from Hungary, PR was well controlled from the 1990s to 2010 (Tong and Chen, 1999, An et al., 2013). Since late 2011, PR outbreaks have occurred in Bartha-K61-immunize pig herds on many Chinese farms and led to huge economic losses (An et al., 2013).
The genome of PRV contains 72 genes that encode 70 different proteins (Klupp et al., 2004). Among these proteins, glycoprotein B (gB) and glycoprotein C (gC) induce cellular and humoral immune responses (Ober et al., 1998, Ober et al., 2000, Wang et al., 2017). Furthermore, the gC is frequently used to analyze the evolutionary relationships of PRV, and the attachment of virus to cells is initiated by the binding of gC to heparan sulfate (HS) proteoglycans (Fonseca et al., 2012, Wang et al., 2015, Ye et al., 2015). The glycoprotein E (gE) is a major virulence determinant of PRV, but is not essential for virus replication (Kimman et al., 1992). In light of this fact, gE-deleted vaccines (Bartha-K61 vaccine) were developed, and the vaccines together with a corresponding serological test to detect antibodies against gE protein have played a key role in a program for the elimination of PR.
Some researches indicated that the causative agent of currently circulating PRV was confirmed to be novel PRV strains which were genetically different from the early Chinese PRV strains, and the Bartha-K61 vaccine did not provide full protection against the PRV variants due to enhanced pathogenicity and genetic differentiation of PRV variants (He et al., 2019, Wang et al., 2019). Furthermore, PRV variants have been spread widely in China, and the PRV-positive rate was various in different years, regions and seasons (Gu et al., 2018, Sun et al., 2018, Zhai et al., 2019, Ma et al., 2020). Therefore, the present study aimed to investigate the molecular epidemiology and biological characteristics of PRV currently circulating in Henan province of China from 2012 to 2019.