A new grant of nearly $3 million will help University of Minnesota College of Veterinary Medicine researchers and collaborators at the University of Edinburgh’s Roslin Institute investigate how porcine reproductive and respiratory syndrome (PRRS) virus evolves and spreads.

The research will help scientists and producers anticipate a herd’s susceptibility to different strains of PRRS virus and accordingly customize mitigation efforts. The data generated could be used to inform future vaccine designs.

The grant is funded jointly by the National Institute of Food and Agriculture, National Science Foundation, National Institutes of Health, and the United Kingdom Government’s Biotechnology and Biological Sciences Research Council. It will cover the next four years of research.

The PRRS virus costs the U.S. swine industry more than $560 million each year. First described in Indiana, North Carolina, Iowa, and Minnesota in the late 1980s, the virus rapidly spreads within barns and between farms. It has since remained one of the industry’s biggest game changers. Since its emergence in the U.S., scientists have worked to reduce its impact.

While a host may build immunity to a certain strain of PRRS virus after infection, that strain can counter-evolve to survive in that host and spread. And viruses often compete for hosts — some are better than others at evading the host’s immunity, depending on what that host is used to. This process is called “multistrain dynamics” and has been investigated extensively in human medicine but has rarely been explored in animals until now. This project aims to help farmers understand how PRRS virus evolves, changes, moves and persists. It also helps producers explore ways of out-maneuvering PRRS virus.

The PRRS virus rapidly evolves and acquires genetic changes over time. However, scientists can study and potentially predict the genetic diversity of PRRS virus in pigs better than they can study other viruses in humans or wildlife because of the rich availability of data — they know where farms are, so they know what the distribution of hosts looks like. They also know how animals are moving between farms, and there is already a lot of ongoing sequencing, so scientists know where and when strains of the virus occur. Researchers don't have this information readily available for studying the same questions in a human virus.

The U-M Veterinary Diagnostic Laboratory has been collecting samples of the PRRS virus for nearly three decades.

The project is partially built on data collected by the Morrison Swine Health Monitoring Project at the university which tracks the occurrence of PRRS virus in roughly 50% of the U.S.’s breeding swine population.

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