Cases of Interspecies Transmission of Influenza A Virus from Swine to Humans

The particular susceptibility of pigs to infection with avian and mammalian influenza viruses allows them to be considered as a mixing vessel where reassortment occurs as a result of coinfection, which promotes the expansion of viral diversity. Although influenza viruses have low pathogenicity in pigs, the outcome of coinfection with other pathogens can be severe, even fatal. Globally, pigs play a key role in the transmission of influenza A viruses between species and the emergence of zoonotic influenza and pandemic viruses. Although human infection with zoonotic influenza viruses is less common than infection with seasonal influenza viruses, there is global concern that these zoonotic viruses may acquire mutations in animals or humans and facilitate efficient animal-to-human trans-mission or persistent human-to-human transmission. The possibility of genetic exchange and interspecies transmission of influenza A viruses is facilitated by the proximity of pig and poultry farms, the production and trade of farm animals and animal products, as well as people working on pig farms. Therefore, ongoing surveillance of both pigs and humans, especially those at increased risk of complications from infection due to exposure at the animal–human interface, and limiting human–pig contact can help prevent severe infections and reduce the public health burden.