Vehicles Play Important Role in Porcine Reproductive and Respiratory Syndrome Virus Transmission

By Tracey Peake

In the battle against disease transmission, pork farmers have to look out for more than just sick pigs. Researchers from North Carolina State University have modeled nine different potential transmission routes for porcine reproductive and respiratory syndrome virus (PRRSV), and found that trucks used to move not only animals, but also farm workers and feed, can be carriers for disease spread.

PRRS, the syndrome caused by the virus, causes respiratory disease and decreased reproduction in pigs, and is the most economically significant disease affecting U.S. swine production.

"We created a novel mathematical model that includes potential transmission routes that haven't been explored in depth," says Gustavo Machado, assistant professor of population health and pathobiology at NC State and corresponding author of a paper describing the work.

Machado and senior postdoctoral researcher Jason Galvis modeled nine modes of between-farm transmission of PRRSV based on data from three swine farms. The modes included farm-to-farm proximity; transmission between farm animals; "re-breaks" for farms with a previous outbreak; between-farm vehicle movements; and animal byproducts in feed ingredients.

The model was used to estimate the weekly number of outbreaks and their locations. Those estimates were then compared to available outbreak data so that the researchers could quantify the contributions of each transmission route.

While pig movements and farm proximity were still the leading causes of disease transmission, the researchers found that the vehicles used to transport pigs were a major contributor to PRRSV spread, contributing up to 20% of infections. Animal byproducts and feed, on the other hand, were found to have little effect on transmission.