Growth characteristics and complete genomic sequence analysis of a novel pseudorabies virus in China

Swine pseudorabies (PR) re-emerged in Bartha-vaccinated pig herds and caused death of millions of piglets in China since the later part of 2011. We isolated a novel pseudorabies virus (PRV), named HNX strain, from the brain of abortion fetuses to diagnose the disease. To reveal the genomic organization and characterize the HNX strain, the complete genomes of HNX and Fa strain, an isolate in the 1960s, were sequenced and analyzed. The genomic size of HNX and Fa strains were 142,294 and 141,930 nt, respectively, with corresponding G + C contents of 73.56 and 73.70 %. The two strains consistently possessed 70 open reading frames. In addition, comparative genomic analysis between HNX and Bartha strains was performed to understand the possible reason of immune failure. The major virulence-associated genes of HNX strain had slight changes, whereas glycoprotein B and glycoprotein C genes of HNX strain had 73 mutations; the homology at the whole genomic level between HNX and Bartha strains was 90.6 %. Genome-wide comparison between HNX and Fa strains indicated that the strains shared about 96.4 % of homology and clustered in a separate Chinese isolate group; the two strains are also distant from the isolates from other countries. Similarity plot and bootscanning analysis of complete genome sequences of nine PRV strains, including HNX and Fa, four newly Chinese strains, and three traditional reference strains, revealed that non-recombination events occurred in the HNX strain. The PRV HNX strain with genomic variations might contribute to the PR outbreak in China since the later part of 2011.