Elimination of porcine epidemic diarrhea virus (PEDV) and porcine delta coronavirus (PDCoV) and validation of a herd infection status classification

PEDV and PDCoV entered the US in 2013 infecting 56% of the sow herds. The PIC multiplication system totaling 92,000 sows in North America had accumulated a record of minimal impact from PRRS or M. hyopneumoniae in past years; but from November 2013 to April 2014, 47% of the breeding herds became infected with PEDV and/or PDCoV. Likely because of their remote location and biosecurity, none of the genetic nucleus or sire line nucleus farms were affected. This abstract summarizes the elimination process in 17 sow farms and the validation of the herd infection status classification system proposed by NPB/AASV.

Once a diagnosis was definite, controlled oral exposure of the breeding herd (including replacement gilts) with the resident live virus began. No pigs entered the herd until viral shedding had ceased based on objective assessments. Piglets were weaned off-site and sanitation was intensified during the project. Fostering between litters was limited to the first 24 hours or ceased altogether. Piglet processing and handling protocols were altered to minimize viral transfer between litters. To monitor transmission in the positive unstable (category I) herds, fecal swabs were collected from 30 different litters and tested by PCR every second week. When three consecutive negative tests were accumulated, the herd was classified as transitionally negative (category II) and sentinel pigs could be introduced. The lack of clinical signs or evidence of infection in the sentinel pigs roaming the alley-ways for five weeks allowed the herd to be classified as provisionally negative (category III). Negative serology test in 30 sentinels or bi-weekly weaned pig PCR testing for six months allowed the herd to recover negative status (category IV).

By December 2014, 100% (17/17) of the elimination programs were successfully completed. It took 20 (7–28) weeks for the herds infected with PEDV and 15 (12–17) weeks for the herds infected with PDCoV to consistently wean PCR-negative pigs. No virus was detected after the introduction of sentinel pigs in category II herds suggesting that PCR testing of pigs due to be weaned is an appropriate indicator for transmission. More than a year later, no new or “reactivated” infections have been detected and 100% of the grow-finish flows have verified negative status and have been introduced to customer populations without incident.

The protocol based on whole-herd exposure, intensive sanitation and one-directional pig movement was able to consistently eliminate PEDV and PDCoV from breeding herds. NPB/AASV proposed classification was a useful and accurate tool to coordinate logistics and communication during the elimination efforts.

Disclosure of Interest: J. P. Cano Conflict with: PIC, T. Riek Conflict with: PIC, R. Thompson Conflict with: PIC, T. Snider Conflict with: PIC, J. Geiger Conflict with: PIC, J. W. Lyons Conflict with: PIC.