Methods of control and elimination of porcine reproductive and respiratory syndrome virus using modified live vaccine in a two-site production system

Abstract

A control and elimination program for porcine reproductive and respiratory syndrome virus (PRRSV) was initiated in a two-site, 1250-female herd with a primary business plan of supplying replacement females to commercial herds. Modified live virus (MLV) PRRS vaccine was used to control field PRRSV, which then allowed total virus elimination from all populations. First, the adult sow population was mass vaccinated, and the sow herd was closed for less than 3 months. When PRRSV-negative offspring were being produced,the nursery was depopulated and pigs at the nursery-finisher site were vaccinated with MLV vaccine. After the herd was "stabilized" (ie, exhibited no horizontal or vertical PRRSV transmission), PRRS-positive and previously exposed animals were gradually removed, and a naive herd was established. Polymerase chain reaction and ELISA serological testing for PRRSV were performed on a sample of the population statistically selected to detect 5% prevalence at a 95% confidence level. However, the elimination program deviated from the original plan by allowing use of field-infected finisher animals as replacement gilts. The group of infected gilts used was monitored closely and replaced with naive replacement gilts when profitable market prices returned. Statistical process control techniques were utilized in the serologic monitoring program.