“It’s important first to understand porcine reproductive and respiratory virus transmission within a herd, and then to evaluate its routes of transmission between herds,” says Scott Dee, DVM, with the Swine Disease Center at the University of Minnesota.

An understanding of the PRRS virus’ persistence and transmission within the breeding herd is critical for successful eradication and/or control of the disease, he says. “The essential component of controlling PRRS is the production of pigs that are free of virus at the time of weaning,” he contends.

Researching the routes of transmission, Dee has divided the issue into high- and low-risk routes.

High-risk routes include:

  • Pigs
  • Boar semen
  • Transportation vehicles and processes
  • Fomites (equipment, boots, boxes, etc.)
  • Insects

Low-risk routes include:

  • Personnel
  • Mammals
  • Birds
  • Meat products

Although some researchers believe that aerosol transmission may play a key role in PRRS virus transmission, Dee says aerosol is still a wildcard.

He adds that sometimes, transmission routes — whether high- or low-risk — work together. “It may not be a single entity that creates exposure.”

Dee points to the following example: If a PRRS-contaminated transport vehicle comes somewhere near a swine premises, you may have insects looking to feed on the debris in that truck. Once that truck is removed, those insects may still be hungry and they’ll fly back to the barn. “You may end up with a coordinated sequence of exposure events, not just a single entity,” he notes.