Some key definitions regarding PRRSv infection, control and elimination
(extracted from Holtkamp et al. 2011, JSHAP v19 n1):
Herd: The population of animals at a defined premises.
Premises: Buildings or areas containing pigs at contiguous locations with common employees, management or both.
Internal multiplication and closed premises: A breeding herd where replacements are born on the premises but are reared at other premises before returning as replacements.
Elimination procedure: Any procedure used to eliminate the PRRSV from a swine herd. Ceasing the entry of PRRSV-positive animals and discontinuing intentional exposure to live virus are necessary elements of all elimination procedures. Here are three broad categories of elimination procedures.
- Complete depopulation and repopulation: Complete removal of all animals from a premises which are cleaned and sanitized prior to reintroduction of PRRSV-negative breeding replacements. Applies to both breeding herds and growing-pig herds
- Herd rollover: Any elimination procedure that relies upon cessation of viral shedding in the population and removal of previously infected animals, with subsequent introduction of negative breeding replace- ments. The premises are not completely depopulated in a herd rollover. Typically, herd rollovers involve herd closure (as de!ned below).
- Incomplete depopulation: Any elimination procedure for a growing-pig herd that relies upon cessation of viral shedding in the population, with subsequent introduction of negative animals and removal of previously infected animals. The premises are not completely depopulated in an incomplete depopulation. Applies to growing-pig herds only.
Initiation of elimination: For breeding herds, initiation of elimination begins when the last seropositive breeding replacements are introduced or when the last intentional exposure to any live PRRSV occurs in the herd, whichever is later. For growing-pig herds, initiation of elimination begins when the last positive pigs are introduced.
Herd closure: A procedure where no breeding replacements, positive or negative, are allowed to enter the breeding herd to facilitate cessation of viral shedding in the population. Closure is usually maintained for at least 6 months. Typically done in herds that are eliminating the PRRSV by herd rollover.
Herd test: The evaluation of a herd based on diagnostic testing of a sample of some (or all) animals in the herd and decision rules to classify the herd as positive or negative.
Weaning-age pigs: Pigs within 7 days before or 3 days a#er weaning, regardless of age.
Negative breeding replacement:
For premises that are entering external replacements sourced from other breeding herds, including those with internal multiplication and closed herds, or internal multiplication and closed premises that temporarily introduce replacements from outside sources, confirmation that replacements are antibody-negative and not infected requires both of the following conditions:
- Replacements must originate from AASV Category III or IV breeding herd premises
- Diagnostic confirmation that negative breeding replacements are seronegative by ELISA and negative for viremia by PCR just prior to entry into the breeding herd
For premises that are entering internal replacements, confirmation that replacements are antibody- negative and not infected requires the following condition:
- Diagnostic confirmation that negative breeding replacements are seronegative by ELISA and negative for viremia by PCR just prior to entry into the breeding herd.