PEDV: Time‐to‐stability
How long does it take a sow herd to achieve stable status post-PEDV
14 January 2025
3 minute read
By: Editor's note: The following is from a presentation by Xiaomei Yue and colleagues at the Department of Veterinary Population Medicine, University of Minnesota, during the 2024 Leman Swine Conference.
The porcine epidemic diarrhea virus (PEDV) was first identified in the United States in April 2013. The epidemic period lasted for approximately 1.5 years, transitioning to endemic levels in 2015. Since then, little work has been published on how long it takes a sow herd to achieve a stable status (time-to-stability or TTS). The objective of this study was to estimate the PEDV TTS in US breeding herds during the epidemic and endemic periods.
PEDV weekly monitoring data originating from 1,028 US breeding herds that report PEDV status regularly between May 1, 2013, and June 30, 2023, were obtained from the Morrison Swine Health Monitoring Project (MSHMP).
Status 1 starts from outbreak detection and goes through end of shedding; TTS is calculated as the number of weeks in positive unstable. Then it changes to positive stable status, Status 2, with the absence of clinical signs and no detectable virus for at least four weeks. Status 2fvi designates positive stable with ongoing gilt field virus exposure.
Mixed-effects Cox proportional hazards models were used to assess the association between TTS and the recorded factors, including season, filtration status, herd size, PEDV status of the herd before the break, whether the site experienced a PEDV outbreak within the previous 6 months, and the total number of prior breaks.
In total, 384 PEDV breaks from 16 production systems were included in this study, with 203 occurring during the epidemic period (May 1, 2013 – December 31, 2014) and 181 during the endemic period (January 1, 2015 – June 30, 2023). Overall, the median TTS was 24 weeks (IQR: 18 - 31) during the epidemic and 14 weeks (IQR: 9 - 22) during the endemic period.
There was a significant difference (p < 0.001) in TTS between the epidemic and endemic period. Factors significantly associated with TTS include the PEDV status of the herd before the outbreak and herd size. Herds breaking from status 2fvi reached stability faster (hazard ratio or HR, 8.6 and 3.6 for epidemic and endemic periods) than herds breaking from status 4 (negative). Larger herds (> 5,000 sows) took longer to reach stability (HR: 0.41 for epidemic and 0.45 for endemic periods) than small herds (< 2,500 sows).
This study provides valuable and objective insights into TTS of PEDV breaks in the US breeding herds, especially at a time when the industry is considering whether this disease could be eradicated from the U.S. swine population. These support decision-making in PEDV control and elimination strategies (e.g., forecasting PEDV elimination timeline, herd closure plan) and farm management such as pig flow management and investment timing.
