Control of PRRS: A Fool’s Errand?

Almost 30 years after the emergence of PRRS in Europe and North America, and more than 20 years after the first vaccine was launched, PRRS is a global threat with increasingly more severe variants.

24 March 2017

3 minute read

By: Ludmila Starostina

Is control of PRRS a fool’s errand, an impossible task? No, control is possible; the key to success is better knowledge of the viral targets of immunity, dynamics of transmission, and mechanisms of immune protection. Transmission is well understood, since interventions that block known routes of transmission, such as semen and air, clearly reduce disease spread. Viral targets of immune protection are starting to emerge. An assumed target, envelope glycoprotein 5 (GP5), is a false promise. The complex of GP2-GP3-GP4 is a viable candidate for neutralizing antibodies. Tools to dissect cytotoxic T cell targets are still primitive. And there are proteins still being discovered in PRRSV that may be critical keys. The lesson learned about PRRSV is to avoid assumptions, keep an open mind, and pay attention to what is happening in the field. What is the immunological lesson? Adults are innately more resistant to infection than young pigs. Knowing why can help us use vaccines more effectively.

Vaccines work by inducing specific humoral and T cell memory. Existing live vaccines are variably effective in type 1 and type 2 protection. Since neutralizing antibodies are generally vital to and predictive of anti-viral protection, and can show high levels of broad PRRSV neutralization, they need to be characterized. The role of genetic and other factors in induction of broad protection needs to be defined. T cell immunity remains a challenge due to lack of tools; progress is slow but steady. More can be learned about the role of genetic variation in immune protection. The trend in control of PRRS today is clearly positive. Prevention of infection by good biosecurity and filtration, and regional control programs combining biosecurity and vaccination, act to reduce the environmental burden of virus. Even when vaccination is not completely protective, it reduces viral loads in animals substantially. Going forward, control of PRRS is not a fool’s errand. It is a fruitful undertaking that will improve as we gain more understanding of the virus and the host pig.

Michael Murtaugh