PRRS 2018-2020 Exponentially Weighted Moving Average (EWMA) by State

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.

Dr. Kikuti and colleagues from the University of Minnesota compare PRRS 2018-20 EWMA patterns of different States.

Keypoints

  • We continue to observe different EWMA patterns across states.
  • Even though an overall higher incidence in colder months is observed, sporadic cases in warmer months were detected throughout the states.
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PRRS EWMA Analysis Review

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.

Today, Dr. Vilalta and other members of the MSHMP team review the characteristics of the Exponential Weighted Moving Average (EWMA) charts for PRRS.

Key Points:

  1. The EWMA chart is a smoothed chart of the percentage of farms that are breaking.
  2. This chart is useful for tracking longitudinal data and for detecting the signals that indicate an “event”.
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Review of Chart 3: PRRS incidence rate by status at break

Key Points

  • Incidence rate takes into account the time a farm is at risk for disease.
  • Chart 3 incidence rate has replaced incidence risk by status which did not account for a farm’s contributed time at risk.
  • While incidence rate is less visually intuitive, it more accurately reflects PRRS outbreak rate by status.
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Yearly incidence rate of PRRS per MSHMP Participating Production System

This week, the MSHMP team is sharing the yearly PRRS incidence rates in the 39 participating systems.

Keypoints

  • The average incidence rate for all systems during the entire period described was 0.27 PRRS outbreaks per farm per year.
  • The incidence rate of PRRS outbreaks within a system varies across years with some participants continuing to have lower incidences.
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Understanding whether PRRS viruses in a neighborhood are closely related

This week, the MSHMP team is sharing results from a study looking at how related PRRSv ORF5 sequences from a same area are.

Key Points

  • 28 space-time clustering of PRRSv based on producers’ routine molecular surveillance were identified in the course of 2010-2019.
  • Being inside or outside a space-time cluster significantly explains the genetic variability of most, but not all cases.
  • Assessing space, time, and genetic relatedness relationships in PRRSV transmission is complex, and overall trends might miss important case information.
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