Pork Checkoff Report Newsletter Article 11/13 Submitted by Dave Wright, D.V.M. Classification of PRRS Status Sometimes a simple question like, “What is your PRRS status?” has a complicated answer. The American Association of Swine Veterinarians has adopted a standardized classification system for the PRRS status of swine herds to eliminate misunderstanding. The following table explains the classification of herd status: Breeding Herds: Category Status I Positive Unstable IIA Positive Stable IIB III Positive Stable Undergoing Elimination Provisional Negative IV Negative Description Positive and shedding field-strain virus No clinical signs; No viremia in weaned pigs (4 consecutive negative PCR tests on weaned pigs) Same as IIA, but herd has initiated elimination by herd closure with intentional exposure to fieldstrain PRRSV or vaccination Negative shedding status confirmed by introduction of naïve replacements that test ELISA negative at least 60 days after introduction to herd Negative shedding and negative exposure—all animals negative to PCR and to ELISA Nursery and Finishing Herds are usually only given positive or negative status but further classification is helpful: Category Status Description I Positive Positive and shedding-from Positive Unstable herds IIA Negative PCR Negative from Positive Stable herds IV Negative Negative and not shedding-from Negative herds ? Negative-Vaccinated Negative on arrival but vaccinated-some mapping systems add an orange (MLV) or red (LVI) halo around the symbol to identify sites that are positive from vaccination or live virus inoculation Producers and veterinarians are encouraged to use this classification system when communicating herd status. Also remember to include the Premises Identification Number to properly identify the site.