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Equine veterinary journal2022; 55(3); 506-514; doi: 10.1111/evj.13865

Estimation of the basic reproduction number for Streptococcus equi spp. equi outbreaks by meta-analysis of strangles outbreak reports.

Abstract: Streptococcus equi spp. equi (S. equi), the cause of strangles in horses, is considered a highly contagious pathogen affecting equines and the equine industry worldwide. Fundamental epidemiological characteristics of outbreaks, such as the basic reproduction number (R ), are not well described. Objective: Estimate R for S. equi in equine populations from outbreak data. Methods: Systematic review and meta-analysis of published and unpublished data. Methods: A literature search for outbreak reports was carried out. Depending on data available in the reports, the early epidemic growth rate or final attack rate (AR) approach was used to estimate the basic reproduction number for that outbreak. Other recorded outbreak characteristics were the type of housing (group vs. individual). An overall estimate for R was computed by meta-analysis. Results: Data from eight outbreaks were extracted from peer-reviewed publications. Data from two additional, non-published outbreaks was also included in the meta-analysis. A conservative estimate for R was 2.2 (95% confidence interval [CI] 1.9-2.5). A less conservative estimate, including outbreaks with a 100% AR for which a lower limit R was estimated, was 2.7 (95% CI 2.1-3.3). Conclusions: Few papers describing longitudinal incidence data were found so most estimates were based on the outbreaks' final size. Several outbreaks had a 100% attack rate and could therefore only be included as a lower limit estimate in the meta-analysis. The reported result therefore may be an underestimation. Conclusions: This estimate for R for S. equi informs parameters for future mathematical modelling, quantifies desired preventive vaccine coverage and helps evaluate the effect of prevention strategies through future modelling studies.
© 2022 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2022-08-09 PubMed ID: 35866343DOI: 10.1111/evj.13865Google Scholar: Lookup
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  • Systematic Review
  • Meta-Analysis
  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research seeks to estimate the basic reproduction number, or contagion parameter (R), of the bacteria Streptococcus equi spp. equi (S. equi) that causes strangles in horses. Using a meta-analysis approach, the observed R was found to be 2.2, suggesting each infected horse could potentially infect two more on average under certain conditions.

Objective and Methods

The research’s objective was to estimate the basic reproduction number (R) of S. equi in horse populations by analyzing data from various outbreaks. This information will help model future outbreaks and evaluate disease prevention strategies.

  • The authors performed a systematic review and meta-analysis of previously published and unpublished data.
  • A literature search was undertaken to find reports related to outbreaks of strangles.
  • Depending on the data available in these reports, two different approaches were used to propagate the outbreaks and estimate R: either the early epidemic growth rate or final attack rate (AR).
  • Other recorded characteristics of the outbreaks, such as the type of housing (group vs. individual), were also considered.
  • An overall estimate of R was computed by implementing a meta-analysis on the data gathered.

Results

  • Data from eight outbreaks was extracted from peer-reviewed publications and two more from unpublished sources, making a total of ten outbreaks for the meta-analysis.
  • A conservative estimate of R resulted in a value of 2.2 (95% confidence interval [CI] 1.9-2.5).
  • A less conservative estimate, factoring outbreaks with a 100% attack rate and providing a lower limit for R, resulted in a value of 2.7 (95% CI 2.1-3.3).

Conclusions

  • There were a limited number of papers that provided longitudinal incidence data, resulting in most estimates being based on the final size of the outbreaks.
  • Several outbreaks presented with a 100% attack rate, but these could only serve as lower limit estimates in the meta-analysis, possibly leading to an underestimation of the true R value.
  • The estimated R value for S. equi will help inform future models of potential outbreaks, identify necessary preventive vaccine coverage, and assist in evaluating the effectiveness of disease prevention strategies.

Cite This Article

APA
Houben RMAC, van Maanen K, Kemp-Symonds JG, Waller AS, Sloet van Oldruitenborgh-Oosterbaan MM, Heesterbeek H. (2022). Estimation of the basic reproduction number for Streptococcus equi spp. equi outbreaks by meta-analysis of strangles outbreak reports. Equine Vet J, 55(3), 506-514. https://doi.org/10.1111/evj.13865

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 55
Issue: 3
Pages: 506-514

Researcher Affiliations

Houben, Rosa M A C
  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
van Maanen, Kees
  • Royal GD, Deventer, The Netherlands.
Kemp-Symonds, Jeremy G
  • Bransby Horses, Bransby, UK.
Waller, Andrew S
  • Intervacc AB, Stockholm, Sweden.
  • Department of Biomedical Science and Veterinary Public Health, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Sloet van Oldruitenborgh-Oosterbaan, Marianne M
  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
Heesterbeek, Hans
  • Department of Population Health Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.

MeSH Terms

  • Horses
  • Animals
  • Streptococcus equi
  • Basic Reproduction Number / veterinary
  • Horse Diseases / epidemiology
  • Streptococcal Infections / epidemiology
  • Streptococcal Infections / veterinary
  • Disease Outbreaks / veterinary

Grant Funding

  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University

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Citations

This article has been cited 2 times.
  1. McGlennon AA, Verheyen KL, Newton JR, van Tonder A, Wilson H, Parkhill J, de Brauwere N, Frosth S, Waller AS. Unwelcome neighbours: Tracking the transmission of Streptococcus equi in the United Kingdom horse population. Equine Vet J 2026 Mar;58(2):533-548.
    doi: 10.1111/evj.14558pubmed: 40684376google scholar: lookup
  2. de la Cuesta-Torrado M, Velloso Alvarez A, Santiago-Llorente I, Armengou L, Nieto F, Ríos J, Cruz-López F, Jose-Cunilleras E. Risk Factors and Long-Term Outcomes in Horses After the 2021 Outbreak of Equine Herpesvirus 1 Myeloencephalopathy, Valencia, Spain. J Vet Intern Med 2025 Mar-Apr;39(2):e70040.
    doi: 10.1111/jvim.70040pubmed: 40055829google scholar: lookup
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