The objective this study was to use mathematical modelling to assess the effectiveness of control strategies for PRRS virus on a pig farm.

In a paper in the American Journal of Veterinary Research, first-named author, Jaewoon Jeong of the University of California-Davis and co-authors there and with Boehringer Ingelheim Vetmedica Inc. explain how they formulated stochastic models to simulate an outbreak of PRRS on a small, medium or large farrow-to-weaning farm in the Midwestern United States.

Control strategies assessed in those models included none (baseline) and various combinations of mass immunisation, herd closure and gilt acclimatisation. Nine different models resulting from the combination of low, moderate, or high PRRS virus virulence and small, medium, or large herd size were simulated.

A stabilised status, the outcome of interest, was defined as the absence of positive PCR assay results for PRRS virus in three-week-old piglets. For each scenario, the percentage of simulations with a stabilized status was used as a proxy for the probability of disease control.

Increasing PRRS virus virulence and herd size were negatively associated with the probability of achieving a stabilised status, the researchers found.

Repeated mass immunisation with herd closure or gilt acclimatisation was a better alternative than was single mass immunisation for disease control within a farm.

Repeated mass immunisation with a PRRS modified-live virus vaccine with herd closure or gilt acclimatisation was the scenario most likely to achieve a stabilised status, concluded Jeong and co-authors. They added that estimation of the cost of various PRRS control strategies is required.

Reference

Jeong J., S.S. Aly, J.P. Cano, D. Polson, P.H. Kass and A.M. Perez. 2014. Stochastic model of porcine reproductive and respiratory syndrome virus control strategies on a swine farm in the United States. American Journal of Veterinary Research. 75:260-267. doi: 10.2460/ajvr.75.3.260

June 2014