Outbreak and epidemic of Getah virus infection in swine by virulence-enhanced GIII variant in Henan, central China in 2024.

The Getah virus (GETV), an emerging mosquito-borne virus, poses a threat to many animal species and probably even humans. Between late July and mid-September, concentrated outbreaks of GETV on pig farms have occurred in multiple regions across Henan, and showed epidemic characteristics. To investigate the genetic characteristics and virulence changes of GETV strains responsible for the GETV epidemic in Henan, a total of 27 GETV strains were isolated from 31 commercial pig farms located in 21 counties. Phylogenetic and sequence alignment analysis results showed that 22 of the isolates formed a distinct cluster within the phylogenetic tree, and the strains in this cluster exhibited 3 amino acid mutations in the non-structural protein nsP3 along with an amino acid mutation in the structural protein E2. Piglet pathogenicity experiments demonstrated that the isolate could induce the characteristic clinical signs of GETV infection in piglets, resulting in 100% mortality. Comparative analysis of pathogenicity in mice showed that the pathogenicity of the GETV GIII variant was significantly enhanced compared with the early isolate. This study is the first to investigate in detail the large-scale, concentrated outbreak and epidemic of GETV infection in pig farms in Henan and confirms that there is a trend of increasing virulence of the GIII variant responsible for this outbreak. The data in this study will contribute to the understanding of the molecular epidemiological characteristics and pathogenicity dynamics of GETV.