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.