Advances in understanding influenza A virus infection in swine: From diagnostics to basic science
Influenza A virus (IAV) is a member of the family Orthomyxoviridae and is considered a major pathogen for a number of species including humans, swine, and avian species. Historically, the potential of avian and swine influenza A viruses, either through direct infection by intact virus or through incorporation of genetic information into human isolates, have presented major zoonotic risks to human health risks with epidemic and pandemic potential (98). Prior to the 2009 pandemic, experts were concerned that high pathogenic avian IAV, particularly H5N1, was going to become established in the human population and that such establishment would lead to a pandemic crisis due to the lack of human population immunity to the avian IAV (24, 96). One hypothesized mechanism by which avian IAV could establish itself in the human population is through adaptation in an intermediate host, such as a pig (50). Because such a possibility may exist, determination of the prevalence of H5N1 infection in the swine populations in regions endemic for highly pathogenic H5N1 viruses is highly desirable.
Though the inherent pathogenicity of an intact wildtype virus for its natural host is evident in field or experimental infections, incorporation of the genetic factor(s) responsible for pathogenicity from one virus to another may result in disease that is just as severe. One such pathogenicity factor is the PB1-F2 protein found in a secondary open reading frame of the PB1 mRNA. The PB1-F2 protein is relatively small when compared to other influenza proteins but is associated with a number of pathogenicity factors, including apoptosis, immunopathology, and secondary bacterial infection (23, 63, 105). Though a fair amount of work has been done to understand PB1-F2 in human and avian isolates, currently little is known about the function and expression levels of PB1-F2 during infection with swine influenza virus isolates. Given the zoonotic potential of swine influenza viruses, it is important to understand the effect that PB1-F2 could have on both human and animal health.