Immunity, diagnosis, and intervention strategies for influenza infections in pigs

Immunity against influenza A virus (IAV) develops rapidly and effectively, as infection normally resolves within 1 week and pigs usually remain protected against reinfection with the same or similar strains. The immune response is characterized by the production of antibodies, which is essential for preventing or reducing infection of the host, while the cellular response is important for viral clearance during the late stages of infection. Maternally derived immunity is important for protecting neonatal pigs clinically, but it can interfere with the development of an effective immune response against IAV infection. Strategies to control influenza infection are directed towards minimizing the clinical impact of IAV infection, and vaccination is the most commonly used measure for control of IAV infections in pigs. Vaccines prevent clinical signs, decrease the number of lesions, lower the economic impact of the disease, and can also reduce shedding, but often they only provide partial cross-protection among strains, due to the growing diversity of influenza subtypes and circulating strains. Because clinical signs of IAV are not pathognomonic, appropriate laboratory diagnostics are needed to differentiate these infections from a variety of respiratory diseases.