Current killed and modified-live-virus (MLV) vaccines for porcine reproductive and respiratory syndrome (PRRS) virus have failed to protect pigs against reinfection with different (heterologous) strains.

New approaches to induce protective anti-PRRS immunity are needed. Studies on other pathogens that primarily infect mucosal tissues, like PRRS virus, have shown that induction of effective local mucosal immunity by direct delivery of vaccines with a potent adjuvant promote protective immunity compared to conventional vaccines given parenterally (subcutaneous, intramuscular). Currently, all PRRS vaccines are administered to pigs intramuscularly.

To generate enhanced efficacy of current MLV vaccines, researchers at the Ohio Agricultural Research and Development Center examined the use of nine potent mucosal adjuvants, in conjunction with Ingelvac PRRS vaccine (Boehringer Ingelheim Vetmedica, Inc.), given intranasally to provide better cross-protective immunity in the respiratory tract of pigs.

Of those nine adjuvants, Mycobac–terium tuberculosis whole cell lysate (free from toxic cell wall components of the bacterium) was chosen based on its anti-PRRS virus mucosal and cell-mediated immune responses. In pigs vaccinated with MLV-PRRS plus M. tuberculosis adjuvant intranasally and challenged with a virulent heterologous PRRS strain MN184, there was an absence of signs of PRRS and pigs gained body weight normally compared to control animals.

In contrast, unvaccinated pigs challenged with the MN184 PRRS strain developed typical PRRS symptoms, including fever, reduced feed intake, lethargy and reduce body weight gain during the first two weeks post-challenge.

These vaccinated pigs also exhibited reduced viremia (infection in the bloodstream) and lung pathology associated with enhanced antibody titers and cell-mediated immune responses.

This research demonstrates the advantages of activating the mucosal immune system of pigs using MLV-PRRS vaccine delivered with a potent adjuvant.

Induction of adequate immune responses in the pig respiratory tract may provide an excellent alternative to reduce PRRS outbreaks.

Researcher: Renukaradhya Goura­pura, Ohio Agricultural Research and Development Center, Wooster, OH. For more information, contact Gourapura by phone (330) 263-3748, fax (330) 263-3677 or e-mail gourapura.1@osu.edu.