Effects of two commercial European modified-live vaccines against porcine reproductive and respiratory syndrome viruses in pregnant gilts

The purpose of this study was to assess the effects of two currently available commercial European-type modified-live virus (MLV) vaccines against porcine reproductive and respiratory syndrome in a reproductive pig model. Sixteen 90-day pregnant gilts were divided into four groups and allocated to one of the following intranasal treatments: group A gilts served as negative controls; group B gilts were exposed to a virulent European field strain; group C gilts were exposed to vaccine strain VP046 Bis and group D gilts to vaccine strain All-183. The results indicated that MLV strains can replicate in breeding animals and have the ability to cross the placenta. In particular, viraemia was detected in all gilts in group C and 2/4 gilts in group D, at least at one time point. In addition, transplacental infection was demonstrated in 3/4 gilts in group C and 2/4 gilts in group D. However, congenital and early postnatal infection did not have a marked detrimental effect on piglet performance when compared to negative controls, and no statistically significant differences were observed in most cases. Conversely, the reproductive performance of gilts in group B was significantly worse than that of the other groups. Specifically, the number of born-alive piglets, the survival rate of piglets during lactation and the mean weight of weaned pigs were significantly lower. It was concluded that the two commercial European-type MLV vaccines tested had no marked detrimental effects in pregnant gilts, although the MLV strains can cross the placenta leading to the birth of congenitally infected piglets.