Just in time to prevent and prepare for seasonal PRRS outbreaks, a team led by North Carolina State University researchers and funded by the Fats and Proteins Research Foundation, along with the University of Minnesota Morrison Swine Health Monitoring Project (MSHMP), funded by the Swine Health Information Center (SHIC), developed and calibrated a mathematical model for transmission of porcine reproductive and respiratory syndrome virus (PRRSV).
Their recently published work demonstrated the contribution of multiple unmeasured routes of PRRSV dissemination, including for the first time the role of animal by-products delivered via feed meals, and multiple transportation vehicle networks. It also provides strong evidence to support the need for cautious, measured PRRSV control strategies for transportation vehicles and, to some degree, feed by-products. The project provides valuable information and opportunities for the swine industry to focus effort on the most relevant modes of PRRSV between-farm transmission.
Researchers examined nine modes of between-farm transmission pathways including:
- Farm-to-farm proximity (local transmission)
- Contact network of batches of pigs transferred between farms (pig movements)
- Four different contact networks of transportation vehicles (vehicles to transport pigs to farms, pigs to markets, feed and crew)
- Amount of animal by-products within feed ingredients (e.g. fat and meat and bone)
- Re-break probabilities for farms with previous PRRSV outbreaks
Their model was calibrated on weekly PRRSV outbreak data managed by MSHMP. Researchers assessed the role of each transmission pathway considering the dynamics of specific types of production (i.e. sow farm, nursery). Results estimated that the networks formed by transportation vehicles were more densely connected than the network of pigs transported between farms. The model also estimated that pig movements and farm proximity were the main PRRSV transmission routes regardless of farm types, but vehicles transporting pigs to farms explained a large proportion of infections:
- Sow = 20.9%
- Nursery = 15%
- Finisher = 20.6%
Vehicles transporting feed represented the highest risk for PRRSV propagation in comparison with other vehicle networks, connecting around 85% of farms.
Animal by-products showed a limited association with PRRSV outbreaks through descriptive analysis, while model results showed the contribution of fat and meat and bone was 2.5% and 0.03%, respectively, of the infected sow farms.
Ultimately, this study provides a better understanding of the role of several transmission routes for PRRSV dissemination and can provide bases to the swine industry to evaluate and strengthen the surveillance of transportation vehicles and feed delivery to better contain the propagation of PRRSV.
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