Virus persistence in pig herds led to successive reassortment events between swine and human influenza A viruses, resulting in the emergence of a novel triple-reassortant swine influenza virus

Abstract

This report describes the detection of a triple reassortant swine influenza A virus of H1_avN2 subtype. It evolved from an avian-like swine H1_avN1 that first acquired the N2 segment from a seasonal H3N2, then the M segment from a 2009 pandemic H1N1, in two reassortments estimated to have occurred 10 years apart. This study illustrates how recurrent influenza infections increase the co-infection risk and facilitate evolutionary jumps by successive gene exchanges. It recalls the importance of appropriate biosecurity measures inside holdings to limit virus persistence and interspecies transmissions, which both contribute to the emergence of new potentially zoonotic viruses.

Figure 1

Unrooted phylogenetic trees of European swine and human influenza A viruses. A HA segment; B NA segment; C M segment; D Concatenation of the five other internal segments (PB2, PB1, PA, NP, NS). Phylogenetic trees were built with Seaview by maximum likelihood with the nucleotide substitution model HKY + G. The H1_avN2 strains described in this study are indicated in bold. Only H1 and N2 subtypes were included in HA (A) and NA (B) trees, respectively.