In the last 9 years, on average 10.2% (Range 3.7% – 22%) of status 4 farms have had a PRRS outbreak during the MSHMP season and in the 2017-2018 season, the cumulative incidence (July to April) is 9.6%.
The lowest PRRS incidence was observed during the 2013/2014 PRRS season; the year that PED entered the US.
PRRS incidence in status 4 farms during the current MSHMP season is not higher than the ones observed in the previous MSHMP seasons.
Reminder: Status 4 sow farms are the farms that considered negative both in shedding and exposure status in the classification document published by the AASV.
Has there been an increase in PRRS outbreaks incidence in status 4 sow farms?
PRRS incidence in status 4 farms from 2009 to April 2018 was compiled and compared with the current MSHMP year using Fisher’s Exact test.
During the current MSHMP year (July 2017- April 2018), 27 status 4 farms have had a PRRS outbreak (6.9% incidence). The average incidence of status 4 farms from 2009 to April 2018 was 9.6%. However, PRRS incidence have varied greatly among years (figure 1). PRRS incidence had its minimum value during the 2013/2014 MSHMP season with a 3.4%. This coincides with the year that porcine epidemic diarrhea virus (PEDv) entered the US.
When comparing the incidence during the 2017/2018 MSHMP year with the incidence observed during the 2015/2016 MSHMP year, a borderline significant difference (p=0.06) was observed.
PRRS incidence in status 4 farms (July 2017 –April 2018) was overall similar to previous years, although slightly higher than July 2016-April 2017, and significantly lower than July 2015-April 2016. Other factors, such as region, may be contributing to the
perception of increased PRRS incidence in status 4 farms.Exploring these factors may help explain the perception of increased