Genetics, Evolution, and the Zoonotic Capacity of European Swine Influenza Viruses

Abstract

The European swine influenza virus lineage differs genetically from the classical swine influenza viruses and the triple reassortants found in North America and Asia. The avian-like swine H1N1 viruses emerged in 1979 after an avian-to-swine transmission and spread to all major European pig-producing countries. Reassortment of these viruses with seasonal H3N2 viruses led to human-like swine H3N2 viruses which appeared in 1984. Finally, human-like swine H1N2 viruses emerged in 1994. These are triple reassortants comprising genes of avian-like H1N1, seasonal H1N1, and seasonal H3N2 viruses. All three subtypes established persistent infection chains and became prevalent in the European pig population. They successively replaced the circulating classical swine H1N1 viruses of that time and gave rise to a number of reassortant viruses including the pandemic (H1N1) 2009 virus. All three European lineages have the capacity to infect humans but zoonotic infections are benign.

Novel triple reassortant H1N2 influenza viruses bearing six internal genes of the pandemic 2009/H1N1 influenza virus were detected in pigs in China

“…The N2 NA genes of these viruses were derived from human H3N2 influenza viruses, whereas the HA genes were derived from classical swine H1N1, avian-like swine H1N1, or human H1N1 influenza viruses. In addition, some H1N2 viruses were humanavian-swine triple-reassortant viruses [24]. Sporadic cross-species transmission of swine H1N2 viruses to humans has been reported in Thailand and Philippines [25].…”

A Phylogeny-Based Global Nomenclature System and Automated Annotation Tool for H1 Hemagglutinin Genes from Swine Influenza A Viruses

“…To do so, we use three first-order descriptors—the 1A classical lineage derived from the 1918 human pandemic viruses, the 1B human seasonal lineage associated with 1990s human-to-swine transmission episodes, and the 1C Eurasian avian lineage associated with viruses introduced to swine in Europe and Asia from wild birds (37). Following this, we identified monophyletic clades in our phylogeny with at least 10 viruses collected over the preceding 5 years: without exception, these clades had statistical support of ≥70% and generally an average pairwise distance of <7% within clade and >7% between clades.…”

Prevalence and characterization of influenza viruses in diverse species in Los Llanos, Colombia

“…In many parts of the world, there is evidence of continued reassortment between pH1N1 and classical swine H3N2 and H1N1 viruses. Several of these reassortants have crossed into humans, 28,29,32,33,34,35,36 the most recent being the novel reassortant H3N2 viruses currently infecting humans in the United States. 28,29,37,38,39 Similarly, swine in Argentina have been found to be infected with pH1N1 and seasonal human reassortants.…”