A controlled influenza A virus transmission experiment was conducted in biosafety level 2 containment from January 23, 2018- February 13, 2018 assessing the respiratory droplet transmission efficiency of A(H3N2)/swine/Ohio/A01354299/2017 from experimentally inoculated pigs to naïve, contact ferrets. This experimental setting models the human-swine interface at agricultural fairs, where human infection with influenza viruses of swine origin has been well documented. Five pigs were housed in a standard enclosure and four ferrets were housed in isolators placed 7.5cm from the pig enclosure. Nasal swab samples from pigs were collected on 0, 1, 3, and 5 days post infection and nasal wash samples from ferrets were collected 0, 2, 4, 6, 8, and 15 days post contact. The whole genome sequences of 15 swine and 12 ferret virus isolates were obtained from respiratory samples cultured on Madin-Darby Canine Kidney cells. Sequencing was performed on an Illumina MiSeq platform and consensus sequences for each gene segment were generated using in-house software at the USDA-APHIS National Veterinary Services Laboratory.

An investigation of antigenic relationships between North American swine H3N2 influenza A viruses (IAV) and human seasonal vaccine strains was conducted to assess the zoonotic risk to humans. Human seasonal H3N2 vaccine strains isolated from 1973 to 2014 (n=20) were obtained from the World Health Organization Global Influenza Surveillance and Response Network through St. Jude Children’s Research Hospital to use for serological assays, such as hemagglutination inhibition (HI) assays. Human seasonal vaccine strains were cultured on MDCK cells or eggs and the HA gene was verified by sequencing on a Sanger method at National Animal Disease Center (NADC). A consensus HA sequence was generated using Geneious Software.