title: Strain predominance following exposure of vaccinated and naive pregnant gilts to multiple strains of porcine reproductive and respiratory syndrome virus.
abstract: Two studies were performed in order to test the relative ability of different strains of porcine reproductive and respiratory syndrome virus (PRRSV) to replicate and cross the placental barrier in pregnant gilts. Study 1 comprised 6 nonvaccinated gilts. Study 2 comprised 8 nonvaccinated gilts and 12 gilts that were vaccinated twice before conception. On, or about, gestation day 90 all gilts were simultaneously exposed to 20 field strains of PRRSV (all strains were distinguishable by restriction fragment length polymorphism (RFLP) patterns). Gilts of study 1 were euthanized on day 7 postpartum. Gilts of study 2 were euthanized on, or about, gestation day 111. All gilts, pigs, and fetuses were tested for the presence and type of strain of PRRSV. Of 128 samples shown to contain PRRSV, 118 contained a single strain, 4 contained 2 strains, and 2 contained a strain or strains for which the RFLP pattern was undecipherable. Only 8 of the 20 strains were isolated from nonvaccinated gilts and their litters. And only 2 of the 20 strains (notably 2 of the same strains isolated from nonvaccinated gilts and their litters), were isolated from vaccinated gilts and their litters. Moreover, 1 of the 2 strains accounted for most (31 of 37; 84%) of the isolates from the vaccinated group. Collectively these results indicate that strains differ in their ability to replicate in pregnant gilts and cross the placental barrier. And they suggest that maternal immunity, although sometimes insufficient to prevent transplacental infection, can exert additional selective pressure.
authors.affiliation: Virus and Prion Diseases of Livestock Research Unit, National Animal Disease Center, USDA, Agricultural Research Service, 2300 Dayton Avenue, P.O. Box 70, Ames, Iowa 50010, USA. klager@nadc.ars.usda.gov
authors.forename: Kelly M
authors.initials: KM
authors.lastname: Lager
authors.forename: William L
authors.initials: WL
authors.lastname: Mengeling
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Wesley
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D000914:Antibodies, Viral / Q000097:blood; D005260:Female; D007112:Immunity, Maternally-Acquired; D018445:Infectious Disease Transmission, Vertical / Q000517:prevention & control / Q000662:veterinary*; D008297:Male; D008431:Maternal-Fetal Exchange; D012150:Polymorphism, Restriction Fragment Length; D019318:Porcine Reproductive and Respiratory Syndrome / Q000145:classification / Q000473:pathology / Q000517:prevention & control / Q000635:transmission*; D019316:Porcine respiratory and reproductive syndrome virus / Q000276:immunology / Q000472:pathogenicity / Q000502:physiology*; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000662:veterinary* / Q000821:virology; D013047:Specific Pathogen-Free Organisms; D013552:Swine; D014611:Vaccination / Q000662:veterinary; D014613:Vaccines, Attenuated; D014765:Viral Vaccines
chemical_list: D000914:Antibodies, Viral; D014613:Vaccines, Attenuated; D014765:Viral Vaccines