Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2009
Publication Date: 5/28/2009
Citation: Vincent, A.L., Swenson, S.L., Lager, K.M., Gauger, P.C., Loiacono, C., Zhang, Y. 2009. Characterization of an Influenza A Virus Isolated from Pigs During an Outbreak of Respiratory Disease in Swine and People at a County Fair in the United States. Veterinary Microbiology. 137(1-2):51-59. Interpretive Summary: Swine influenza virus (SIV) is one of the primary causes of respiratory disease in growing pigs and can lead to major economic losses. There is a potential for people exposed to SIV to become infected, although this event is far less common than the spread of human influenza virus from person to person. In this paper, we studied a virus from pigs that also infected 2 people during a county fair in 2007. The virus caused disease in pigs, spread from pig to pig, and the pigs were shown to be contagious for up to 7 days after infection. The characteristics of this virus suggest opportunity for exposure of people in contact with pigs infected with this virus. Closer monitoring of pig and human populations for this and other SIV is warranted.
Technical Abstract: In August 2007, pigs and people became clinically affected by an influenza-like illness during attendance at an Ohio county fair. Influenza A virus was identified from pigs and people, and the virus isolates were characterized as swine H1N1 similar to the swine H1N1 viruses currently circulating in the U.S. pig population. The swine isolate, A/SW/OH/511445/2007 (OH07), was evaluated in an experimental challenge and transmission study reported here. Our results indicate that the OH07 virus was pathogenic in pigs, was transmissible among pigs, and failed to cross-react with many swine H1 anti-sera. Naturally exposed pigs shed virus as early as 3 days and as long as 7 days after contact with experimentally infected pigs. This suggests there was opportunity for exposure of people handling the pigs at the fair. The molecular analysis of the OH07 isolates demonstrated that the 8 gene segments were similar to those of currently circulating triple reassortant swine influenza viruses. However, numerous nucleotide changes leading to amino acid changes were demonstrated in the HA gene and throughout the genome as compared to contemporary swine viruses in the same genetic cluster. It remains unknown if any of the amino acid changes were related to the ability of this virus to infect people. The characteristics of the OH07 virus as well as the documented pig-to-human transmission warrant close monitoring of the spread of this virus in pig and human populations.