Reassortant between Human-Like H3N2 and Avian H5 Subtype Influenza A Viruses in Pigs: A Potential Public Health Risk

Abstract

BackgroundHuman-like H3N2 influenza viruses have repeatedly been transmitted to domestic pigs in different regions of the world, but it is still uncertain whether any of these variants could become established in pig populations. The fact that different subtypes of influenza viruses have been detected in pigs makes them an ideal candidate for the genesis of a possible reassortant virus with both human and avian origins. However, the determination of whether pigs can act as a “mixing vessel” for a possible future pandemic virus is still pending an answer. This prompted us to gather the epidemiological information and investigate the genetic evolution of swine influenza viruses in Jilin, China.MethodsNasopharyngeal swabs were collected from pigs with respiratory illness in Jilin province, China from July 2007 to October 2008. All samples were screened for influenza A viruses. Three H3N2 swine influenza virus isolates were analyzed genetically and phylogenetically.ResultsInfluenza surveillance of pigs in Jilin province, China revealed that H3N2 influenza viruses were regularly detected from domestic pigs during 2007 to 2008. Phylogenetic analysis revealed that two distinguishable groups of H3N2 influenza viruses were present in pigs: the wholly contemporary human-like H3N2 viruses (represented by the Moscow/10/99-like sublineage) and double-reassortant viruses containing genes from contemporary human H3N2 viruses and avian H5 viruses, both co-circulating in pig populations.ConclusionsThe present study reports for the first time the coexistence of wholly human-like H3N2 viruses and double-reassortant viruses that have emerged in pigs in Jilin, China. It provides updated information on the role of pigs in interspecies transmission and genetic reassortment of influenza viruses.

Susceptibility of swine to H5 and H7 low pathogenic avian influenza viruses

“…Experimental studies have demonstrated influenza reassortment using pigs as a mixing vessel 8, 9. Furthermore, genetic‐based surveillance and epidemiologic reports have highlighted natural reassortment events within a narrow time frame, location, and likely group of pigs 10, 11, 12…”

Antiviral Responses by Swine Primary Bronchoepithelial Cells Are Limited Compared to Human Bronchoepithelial Cells Following Influenza Virus Infection

“…The ongoing risk that viral reassortment poses was highlighted by the emergence of the 2009 triple reassortant swine-origin H1N1 pandemic virus [6]. Furthermore, the highly pathogenic H5N1 avian influenza virus has recently crossed the species barrier to infect humans resulting in a high mortality rate, and reassortant viruses with internal genes of avian H5 lineage have been identified in swine, raising concern about the pandemic potential of reassortant H5 viruses [7,8]. …”

Critical role of segment-specific packaging signals in genetic reassortment of influenza A viruses

“…Similarly, RGd-RV with the HA gene from H5N1 virus in the H1N1pdm2009 genetic background replicated efficiently in primary human respiratory epithelial cells and caused 100% mortality in mice (19). However, phylogenetic analyses of natural or experimental reassortant viruses have shown that the HA segment from avian, swine, or equine viruses was never incorporated alone in the genetic background of a human virus (13,14,20): The HA segment is packaged with additional groups of gene segments depending on the viral subtypes involved in the coinfection process (13,14).The inability to obtain a virus containing a nonhuman HA gene in an otherwise human genetic background, in contrast with the ability to produce "7+1" RGd-RV with a high yield of replication, suggests that the reassortment process might be restricted by suboptimal compatibility between the vRNA-packaging signals (10).…”