Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2002
Publication Date: N/A
Interpretive Summary: Porcine reproductive and respiratory syndrome (PRRS) is one of the most costly diseases faced by the United States livestock industry. Although vaccination has been one of the ways veterinarians and swine producers have tried to prevent this disease, numerous epidemics in vaccinated herds have raised a question as to their reliability under farm conditions. In the study reported here we have looked at one of the possible reasons for vaccine failure, namely the lack of cross protection among different strains of PRRS virus (PRRSV). Our results suggest that vaccines may have to contain multiple strains of PRRSV to be most effective. The development of better vaccines would save swine producers millions of dollars annually.
Technical Abstract: Objective: To determine strain specificity and efficacy of the immune response of pigs following vaccination with selected strains of porcine reproductive and respiratory syndrome virus (PRRSV). Animals: 30 specific-pathogen-free pigs. Procedure: The study comprised 5 groups of 2-to 3-week-old pigs (6 pigs/group). On day 0, groups III, IV, and V were vaccinated with attenuated versions of PRRSV strains 8, 9, and 14, respectively. On day 21, groups II, III, IV, and V were exposed to a composite of the virulent versions of these same 3 strains. At necropsy (day 35) lungs and selected lymph nodes were examined for virus-induced changes. Blood (serum) samples obtained at weekly intervals and lung lavage fluids obtained at necropsy were tested for the presence of PRRSV and its strain identity. Results: The strain of PRRSV identified in the sera of pigs after vaccination, but before exposure to virulent PRRSV, was always the strain with which the pig had been vaccinated. Conversely, with 1 exception, the strain or strains of virus identified in sera and lung lavage fluids after exposure to virulent PRRSV were never the strain with which the pig had been vaccinated. There was no clear evidence that vaccination with any of the 3 attenuated strains provided immunity against the multi-strain exposure. Conclusions: Vaccine-induced immunity against PRRSV is at least partly strain related when pigs are exposed to virulent virus as early as 3 weeks after vaccination. Clinical relevance: Multi-strain vaccines may be necessary to provide timely and effective immunity.