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.