Molecular epidemiology of outbreak-associated pseudorabies virus (PRV) strains in central China

In several parts of China, there have been a large number of pseudorabies (PR) outbreaks which have devastated many swine farms even though the herds had been previously immunized with gE-deleted vaccines (Bartha-K61). The emergence of these outbreak-associated PRV strains might indicate that Bartha-K61 vaccine could not provide effective protection and poses challenges for current serologic diagnostics of anti-PRV antibodies. Here, we performed phylogenetic analyses based on partial gE, gB, and gC genes to provide information about the molecular epidemiology, diagnostics, and immune protection in these outbreak-associated PRV strains. Our results indicated that the maximal nucleotide sequence divergence for gE, gB, and gC genes are 1.7, 0.4, and 2.7 % within the cluster where outbreak-associated PRV strains were located, and are 2.3, 2.7, and 7.6 % with other clusters in the phylogenetic trees, respectively. Phylogenetic analyses revealed that gE, gB, and gC genes of the twelve outbreak-associated PRV strains clustered to a relatively independent branch of the tree, and evolved from the same ancestor with strains Ea-China-1999, Fa-China-2001, and BJ-China-2008. The genetic relationship between these outbreak-associated PRV strains and strain Bartha is not close which may genetically explain the emergence of PR outbreaks in Bartha-K61-vaccinated swine farms. We suggest that these outbreak-associated PRV strains originate from earlier strains in local regions in China.