A study led by Dr. Dennis Makau and the VanderWaal lab was recently published in the journal of Transboundary and Emerging Diseases. In this study, we aimed to quantify the contribution of pig movements to the risk of occurrence of PRRSV Type 2 (RFLP 1-7-4 , a sublineage of lineage 1[L1A]) in the United States.
Methods
We performed temporal network autocorrelation modelling using data on animal movements and 1,761 PRRSV ORF5 sequences linked to 494 farms from a dense pig production area in the United States between 2014 and 2017. A farm’s current and past exposure to L1A and other PRRSV variants was assessed through its primary and secondary contacts in the animal movement network. A farm was defined as L1A positive if at least one L1A PRRSV sequence had been isolated on the farm in a given six-month period.
Key findings and their relevance
Both primary and secondary farm contacts via animal movements significantly increased the odds of L1A occurrence on the farm (10% and 23% respectively). Outward shipment of animals from a farm increased the likelihood of L1A occurrence on a farm by 3%; calling attention to potential breaches in biosecurity associated with animal shipments.
Downstream farms receiving animals from sow farms had a 36% reduction in the likelihood of L1A occurrence if the sow farm had utilized MLV or LVI ~1 year prior. This suggests that disease mitigating measures and enhanced immunity in sow farms has a carry-over effect on the occurrence of L1A in downstream farms.
Overall, coordinated disease mitigation measures and surveillance at all production levels for farms connected by animal movements would likely be more effective than individual farm-based interventions.