The effect of season on PRRS time-to-stability in the Midwestern United States

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

Key Points

  • Seasonal conditions may effect the time to stability of a farm
  • Understanding seasonal effects on time to stability can help producers and veterinarians plan herd closures

This week, we are sharing a report by the MSHMP team in collaboration with Dr. Andreia Arruda from the Ohio State University regarding the impact of seasons on PRRS time-to-stability.

The time needed between an outbreak and consistently weaning porcine reproductive and respiratory (PRRS) virus PCR negative pigs is referred to as time-to-stability (TTS). In this analysis we describe differences in TTS according to the season when the PRRS outbreak occurred in farms located in the Midwestern United States.

161 PRRS outbreaks in 82 sow farms were classified based on the date of the outbreak:

  • March 21st to June 20th: Spring
  • June 21st to September 20th: Summer
  • September 21st to December 20th: Autumn
  • December 21st to March 20th: Winter

TTS was calculated as the time from the reported PRRS outbreak to the time of the last PRRS PCR negative result in wean-age pigs.

A significant difference was detected in TTS among seasons. The median TTS was higher in spring and summer, compared to autumn and winter.

An explanation for the observed TTS difference among seasons may be found in environmental survivability of the virus as for PRRS outbreaks that occur during spring or summer, the last phase of the stability process coincides with the arrival of winter where the reduced ventilation and decreased temperature within the farm may favor PRRS survival resulting on a lower likelihood of elimination during this time.

PRRS time to stability season

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