Influenza A(H3N2) Virus in Swine at Agricultural Fairs and Transmission to Humans, Michigan and Ohio, USA, 2016

Abstract

In 2016, a total of 18 human infections with influenza A(H3N2) virus occurred after exposure to influenza-infected swine at 7 agricultural fairs. Sixteen of these cases were the result of infection by a reassorted virus with increasing prevalence among US swine containing a hemagglutinin gene from 2010-11 human seasonal H3N2 strains.

Keywords: Michigan; Ohio; RNA viruses; United States; agricultural fair; animal population groups; animals; disease outbreaks; influenza A virus; livestock; public health; respiratory infections; swine; zoonoses.

Figure 1

Phylogenetic relationships inferred for subtype H3 hemagglutinin genes of 2 distinct lineages (indicated on the right of the tree) from influenza A viruses isolated from swine and humans at agricultural fairs in Ohio and Michigan, USA, 2016. Isolates recovered are shown as squares for swine and circles for humans; colors indicate the fair attended. Scale bar indicates nucleotide substitutions per site; collapsed clades within each lineage are monophyletic clades of swine H3 HA genes.

Figure 2

Timeline of detection of human and swine influenza A virus isolates at agricultural fairs in 2016. Isolates recovered are shown as squares for swine and circles for humans; colors indicate the fair attended. One person was exposed to pigs at 3 fairs (C, E, and H). Fair H is an eighth location not described in this study.