Efficacy of a Spanish modified live virus vaccine against homologous porcine reproductive and respiratory syndrome virus infection

The objective of this study was to determine the protective properties of the Spanish MLV vaccine Amervac-PRRS (R) against porcine reproductive and respiratory syndrome virus (PRRSV) infection with the homologous wild-type strain 5710. The experimental design comprised eighteen 3-week old pigs randomly divided into three groups. Animals from group A received one dose of MLV vaccine Amervac-PRRS (R) on days -42 and -21. Animals from groups B and C served as infected and uninfected controls, respectively. On day 0, pigs from groups A and B were intranasally challenged with homologous strain 5710 and 18 days after challenge all pigs were euthanized. The results reported in this study show that, although the titre of neutralizing antibodies elicited by vaccination was modest, MLV vaccine Amervac-PRRS (R) provided protection against homologous PRRSV infection and drastically reduced post-challenge viremia and completely block PRRSV dissemination to peripheral tissues.