title: Comparative safety and efficacy of attenuated single-strain and multi-strain vaccines for porcine reproductive and respiratory syndrome.
abstract: The objective of this study was to compare the efficacy and safety of single-strain and multi-strain vaccines for the prevention of the respiratory facet of porcine reproductive and respiratory syndrome. The study comprised six groups of pigs (A through F, eight pigs per group). At the beginning of the study (Day 0) Groups C and D were vaccinated with a single-strain vaccine, and Groups E and F were vaccinated with a multi-strain vaccine. The multi-strain vaccine contained five attenuated strains of PRRSV including the strain used as the single-strain vaccine. On Day 28 Groups B (nonvaccinated/challenged control), D, and F were challenged with a highly virulent field strain of PRRSV that was unrelated to any of the strains used for vaccination. Group A was kept as a nonvaccinated/nonchallenged control. On Day 42 all pigs were necropsied. Their lungs and lymph nodes were examined for virus-induced changes. Serum samples obtained at weekly intervals during the study and lung lavage fluids obtained at necropsy were tested for the presence and titer of PRRSV. Serum samples were also tested for antibody. The presence and severity of clinical signs and lesions were the primary means by which vaccine efficacy and safety were evaluated. Both vaccines provided a high level of protective immunity to challenge. However, appreciable lymph node enlargement in pigs vaccinated with multi-strain vaccine, with or without subsequent challenge, raised a question as to its safety. Collectively these results indicate that both single-strain and multi-strain attenuated PRRSV vaccines can be effective immunogens, but additional studies in regard to safety are needed before multi-strain vaccines can be recommended for routine field use.
authors.affiliation: Virus and Prion Diseases of Livestock Research Unit, National Animal Disease Center, PO Box 70, USDA, Agricultural Research Service, Ames, IA 50010, USA. bbmengeling@aol.com
authors.forename: William L
authors.initials: WL
authors.lastname: Mengeling
authors.forename: Kelly M
authors.initials: KM
authors.lastname: Lager
authors.forename: Ann C
authors.initials: AC
authors.lastname: Vorwald
authors.forename: Deborah F
authors.initials: DF
authors.lastname: Clouser
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D001992:Bronchoalveolar Lavage Fluid / Q000821:virology; D004279:DNA, Viral / Q000737:chemistry / Q000235:genetics; D004435:Eating; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D008168:Lung / Q000473:pathology / Q000821:virology; D008198:Lymph Nodes / Q000473:pathology / Q000821:virology; D016133:Polymerase Chain Reaction / Q000662:veterinary; D012150:Polymorphism, Restriction Fragment Length; D019318:Porcine Reproductive and Respiratory Syndrome / Q000097:blood / Q000276:immunology / Q000517:prevention & control*; D019316:Porcine respiratory and reproductive syndrome virus / Q000235:genetics / Q000276:immunology* / Q000472:pathogenicity; D013047:Specific Pathogen-Free Organisms; D013552:Swine; D014611:Vaccination / Q000379:methods / Q000662:veterinary*; D014613:Vaccines, Attenuated / Q000276:immunology / Q000627:therapeutic use; D014765:Viral Vaccines / Q000276:immunology* / Q000627:therapeutic use; D014774:Virulence
chemical_list: D000914:Antibodies, Viral; D004279:DNA, Viral; D014613:Vaccines, Attenuated; D014765:Viral Vaccines