Infection Dynamics of IAV in Endemic Infection Scenarios,Kevin Vilaca from South West Ontario Veterinary Services

Influenza Virus A (IAVsw) is a viral pathogen that is a frequently occurring pathogen in all ages of growing and breeding pigs. Many years ago most outbreaks were epidemic in nature with widespread infection followed by clearing immunity and virus elimination. Larger herd sizes have contributed to endemic infection of herds being more common. These UK researchers wanted to assess IAVsw infection dynamics and evolution by carrying out a longitudinal surveillance study for over 18 months on two enzootically infected, intensive, indoor, and multi-site pig production flows. Frequent sampling of all production stages using individual and group sampling methods was performed, followed by virological and immunological testing and whole-genome sequencing.

The researchers found the following:

• The main reservoir of IAVsw in these herds was identified as a continuous year round infection in the weaned pigs between 4 and 12-weeks old .
• Infection levels were not uniform and times of increasing exposure at the herd level were often associated with reduced viral prevalence and then a subsequent “rebound” infection.
• In this particular study a single virus subtype was maintained on each farm for the entire duration of the study. Viral evolution was characterised by long periods of time with little genetic change followed by shorter periods of rapid genetic change coinciding with increasing exposure within the herd.
• Mutations associated with surface glycoproteins was consistent with antigenic drift. Some amino acid substitutions in the internal gene products were observed as well as some reassortment exchange of internal gene segments from newly introduced strains.
Take Home Messages:
• Because there can be prolonged periods with modest genetic change associated with genetic drift followed by an uptick in more profound genetic change it is important to conduct period surveillance targeted at detecting IAVsw genetic change that could affect herd immunity.

Reference: Paula Lagan , Michael Hamil , Susan Cull , Anthony Hanrahan , Rosanna M Wregor , Ken Lemon Swine influenza A virus infection dynamics and evolution in intensive pig production systems Virus Evol . 2024 Feb 27;10(1):veae017. doi: 10.1093/ve/veae017. eCollection 2024.