CONTROL OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS TRANSMISSION - HANDLING INFECTED SEEDSTOCK

One of the greatest challenges facing practitioners is how to handle o perations involving seedstock infected with porcine reproductive and r espiratory syndrome (PRRS) virus. The primary vector for transmission of the virus is the infected pig; however, seminal transfer and aeroso l transmission may occur. Before any decisions are made regarding the status of a herd, an understanding of PRRS virus serology is required. Currently, the most commonly used test is the indirect fluorescent an tibody (IFA), which measures exposure to the virus. The test cannot me asure the level of immunity in animals, nor can it predict whether tes ted animals are carriers of PRRS virus. Most diagnostic laboratories i n the United States have set up the IFA test for detection of antibodi es to the American strain of the virus only. Differences between the A merican and European (Lelystad) strains have been reported. Serologic data from three cases are presented to demonstrate the use of the IFA test on a practical basis. Along with monitoring previously infected a nimals, the use of sentinels (animals acquired from another herd that are equal in health status to the infected herd and negative for PRRS virus) can be helpful. The following criteria will be met if the virus does not actively spread within the population: titers in previously infected animals will decrease, seroconversion will not be evident in the sentinels, and all virus isolation attempts will be negative. Thes e criteria form the basis of the noncarrier pig.