Brent Jones from South West Ontario Veterinary Services,Dynamics Of PRRSV Spread Within A Region

Porcine reproductive and respiratory syndrome virus (PRRSV) is still one of the most significant health problems in the North American pork production industries. Despite some significant  improvements in the ability to genetically characterize PRRSV virus it is sometimes unclear whether PRRSV infections are a product of viral circulation within a farm, within a production systems (local) or across production systems (external). These US researchers examined the spread of PRRSV within and among pig farms within in three commercial pig production systems located within one region.

The researchers found the following:

  • PRRSV genetic diversity in that particular region had actually declined since 2018.
  • PRRSV gene sequence comparison and PRRSV family tree analysis indicated that there was  frequent transmission of PRRSV from one production system to another.
  • Within the region being studied ,PRRSV dissemination occurred mostly through transmission between farms of different production companies
  • PRRSV dissemination occurred most frequently from November until May.
  • Within production systems, PRRSV dissemination occurred mainly through regular pig flow including pig movement from sow to nursery and then to finisher farms. Having said that there was some evidence of PRRSV dissemination from finisher to sow and finisher to nursery
  • Farms were more likely to disseminate PRRSV when
    • pig density was from 500 to 1000 pig/km2
    • farms were located within 0.5 km and 0.7 km from major roads
  • Farms were less likely to disseminate PRRS when
    • the farms at elevation between41 and 61 meters
    • denser vegetation around the farms acted as dissemination barriers.

Take Home Messages:

  • At least within the region that was studied , farm proximity was a driver on PRRSV spread.
  • Farm location and farm geographic characteristics can help to forecast the likelihood of PRRSV dissemination from that infected location.

Submitted by Dr. Brent Jones

Ref: Manuel Jara , David A Rasmussen , Cesar A Corzo , Gustavo Machado .  Porcine reproductive and respiratory syndrome virus dissemination across pig production systems in the United States Transbound Emerg Dis . 2020 Jul 13. doi: 10.1111/tbed.13728. Online ahead of print.