Two research 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. (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 AZ 23 their litters) were isolated from vaccinated gilts and their litters. Moreover 1 of the 2 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 AZ 23 UPK1B claim that maternal immunity although insufficient to avoid transplacental disease may exert additional selective pressure sometimes. Intro In 1994 the first vaccine for porcine reproductive and respiratory symptoms (PRRS) became commercially obtainable. It comprised a reasonably virulent field stress of PRRS AZ 23 disease (PRRSV) that were attenuated by serial passing in cell tradition. Early reviews indicated it and additional attenuated-virus vaccines created soon thereafter had been effective in avoiding the reproductive element of PRRS (1 2 3 Nevertheless newer observations specifically those made because the introduction of atypical or severe PRRS in nov 1996 (4 5 possess emphasized that vaccine-induced immunity may also be only incomplete (4) and its own effectiveness will probably depend on many possibly interrelated features from the field stress to that your vaccinate is subjected. Included in these are antigenic homology using the vaccine strain rate of in vivo replication and propensity for transplacental infection. All of these could be statistically evaluated in relative terms for a group of PRRSV field strains by exposing a large number of AZ 23 vaccinated and nonvaccinated gilts to each strain. However another potentially useful less expensive and perhaps more meaningful approach would be to simultaneously expose a smaller number of pregnant gilts (vaccinated and nonvaccinated) to a group of strains and then determine which strain or strains predominated in maternal and fetal blood and tissues. Several studies in our laboratory have indicated that restriction fragment length polymorphism analysis (RFLP) is a reliable method to identify strains of PRRSV that are defined by their genetic homology. Although there are temporal AZ 23 changes in RFLP patterns as evidenced by their appreciable number among field isolates of the virus (6 7 8 the incidence of change is apparently low. Notably no changes were identified when pigs were infected experimentally and kept in isolation for as long as 13 wk (8). Therefore it is possible under laboratory conditions to confirm with reasonable certainty the presence of a particular strain or strains in samples obtained from pigs previously exposed to multiple strains of the virus. In the studies reported here RFLP was used to determine the relative ability of different strains of PRRSV to replicate in vivo and to cross the placental barrier in vaccinated and nonvaccinated gilts. During gestation each gilt was exposed simultaneously to 20 field strains each with a unique RFLP pattern. All gilts were subsequently euthanized and they and their litters were tested for the presence and strain (or strains) of the virus contained in blood and other selected samples. Materials and methods Experimental design The objective of study 1 was to evaluate the consequences of a 20-strain PRRSV challenge of na?ve pregnant AZ 23 gilts. Six gilts (identified as group A) bought from a industrial specific-pathogen-free herd (plantation A) had been one of them research. In the past several years the foundation herd have been examined and discovered free from antibody for PRRSV repeatedly. Each gilt was examined and found free from antibody for PRRSV instantly before and after appearance at our study facility (Country wide Animal Disease Middle NADC). These were bred to 2 boars that were bought through the same herd. At or around gestation day time (GD) 90 these were subjected concurrently to 20 field strains of PRRSV. Bloodstream was gathered from each gilt before publicity at 7 d after publicity (GD 97) and soon after.