The objective of this study was to describe porcine reproductive and respiratory syndrome virus (PRRSV) variability within farms using farms of different demographic types (breeding and growing pig herds) and PRRS management strategies (vaccination, active outbreaks) over a long-term time span; and to investigate whether PRRSV variability has an impact on health and production outcomes.

We enrolled five farms across four U.S. states for this study and followed them for a period between 6 and 12 months. We took several sample types, focusing on those that are commonly used by veterinarians and farm personnel (processing fluids for breeding herds and oral fluids for growing pig herds), and a non-traditional sample type (tonsil scrapings), and submitted the samples to RT-PCR testing and both ORF5 and whole-genome (WGS) sequencing.

Our key results were that on ORF5 sequencing, up to three different PRRSV lineages could be found in a single sampling event (month) for single farms. Additionally, we reported different PRRSV lineages detected from month-to-month for most herds. We also reported that tonsil scrapings appeared to be a useful sample type for PRRSV detection in growing pig herds (regardless of vaccination status), but not for breeding herds, in which processing fluids appeared to be best. We were not able to obtain WGS from our samples.

The take-home message from our study was that sequencing results based on only one sequenced sample per site for a given point in time should be interpreted with caution; especially when trying to make conclusions regarding the source of new outbreaks and the possibility of PRRS re-emergence in swine herds. Sequencing multiple samples in a sampling event would likely give a more comprehensive picture of PRRSV diversity within swine herds.

Contact Information: Andreia Arruda (Assistant Professor, The Ohio State University), e-mail contact: [email protected]