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Study: Fair-related swine and human H3N2 viruses closely match

Researchers report that swine and human influenza A/H3N2 viruses associated with an Ohio county fair held in July make a nearly perfect genetic match, suggesting that there is almost no biological barrier to prevent such viruses from passing between humans and pigs.

The authors sequenced the genomes of H3N2 viruses isolated from pigs that were exhibited at the fair and from several people who were infected with strains of variant H3N2 (H3N2v, the term for the human version) after participating in or visiting the fair. They found that the genomes were more than 99% the same, according to their report in Emerging Microbes and Infections.

The human cases were among 306 H3N2v cases reported by the Centers for Disease Control and Prevention (CDC) since Jul 12 of this year. The vast majority of these occurred in young people who were involved in agricultural fairs.

The cases have mostly been fairly mild, and no sustained human-to-human transmission has been seen. But they have prompted health officials to warn people at risk for flu complications to stay out of swine barns at fairs, and fair visitors and participants have been urged to take special precautions if they have exposure to pigs.

Andrew S. Bowman, DVM, of The Ohio State University (OSU), first author of the new study, said it is the first study in a peer-reviewed journal to compare the genomes of H3N2 viruses recovered from people and pigs in connection with county fair-related cases. The research team also included scientists from Minnesota and Iowa.

The H3N2 viruses in the fair-related cases, both swine and human, carry the M or matrix gene from the 2009 H1N1 pandemic virus. In the current study, the authors call the swine-origin strain H3N2pM.

In the study, the research team gathered nasal swabs from 34 pigs that were randomly selected on the last day of the fair, Jul 28, about a week after the pigs arrived there. The fair was not identified. None of the pigs had obvious signs of illness at the time of the sampling, although exhibitors said some pigs had been sick 3 to 5 days earlier and a few had been sent home.

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