Incidence Risk and Incidence Rate: an Overview

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. Juan Sanhueza helps us understand better two epidemiologic concepts: the incidence risk and incidence rate.

Key Points

  • Incidence risk is a measure of disease occurrence over a defined period of time. It is a proportion, therefore takes values from 0 to 1 (0% to 100%)
  • Incidence rate takes into account the time an individual is at risk of disease. It is not a proportion since it defines the number of cases per animal or farm time at risk.
  • Incidence risk and incidence rate are often confused. Incidence risk and rate are numerically the same when the period at risk does not vary across individuals being studied.
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Senecavirus A continues to be present in the United States swine herd

This week, Dr. Guilherme Preis, graduate student at the University of Minnesota with Drs. Corzo and Vannucci is sharing an update on the prevalence of Senecavirus A in the United States.

Key Points

  • Senecavirus A continues to present in the US at low levels. 
  • Sow herds are more likely to test positive than growing pig herds. 
  • SVA positive herds tend to have a large number of positive samples. 
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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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Can 2 strains of PRRSv be highly homologous but have distinct virulence?

Key points

  • Two novel HP-PRRSV variants (XJ17-5 and JSTZ1712-12) that have the new genetic feature of 150-amino-acid deletion in nsp2 were identified.
  • Even though XJ17-5 and JSTZ1712-12 isolates share high genomic homology, they had distinct pathogenicity for piglets.
  • Fragment comparisons identified 34 amino acid differences between the two isolates which might be related to distinct virulence.
Continue reading “Can 2 strains of PRRSv be highly homologous but have distinct virulence?”

PRRSV 1-7-4 ORF5 diversity over time

This week, the MSHMP team is looking at 16 years of genetic diversity of ORF-5 from the PRRS virus sequences submitted by the MSHMP participants

Key Points

  • PRRSV ORF5 sequence monitoring over time contributes to the understanding of pathogen evolution.  
  • Range of PRRSV 1-7-4 percent divergence has decreased over the last 16 years between 2003 and 2019, which is consistent with lineage turnover previously described.
  • PRRSV 1-7-4 can belong to a specific lineage or sublineage, 1A being the most common currently.
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