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Journal of veterinary internal medicine2018; 32(1); 459-464; doi: 10.1111/jvim.15037

Decreased Clinical Severity of Strangles in Weanlings Associated with Restricted Seroconversion to Optimized Streptococcus equi ssp equi Assays.

Abstract: Streptococcus equi ssp. equi causes characteristic clinical signs that are most severe in young horses, including fever, purulent nasal discharge, and lymph node abscessation in the head region. Objective: Clinical, serologic, and microbiologic factors related to unexpectedly mild disease severity in a natural outbreak of strangles in immunologically naïve weanlings were investigated. Methods: One-hundred and twelve warmblood weanlings. Methods: Prospective longitudinal observational study of a natural outbreak of strangles. The entire cohort was examined at the peak of the outbreak by deep nasal swabs for culture and quantitative PCR (qPCR) for the presence of S. equi and clinically and serologically in a sequential manner by an optimized ELISA from the index case throughout the outbreak until resolution. Descriptive statistics were calculated and comparisons made using a nondirectional Wilcoxon signed-rank test. Results: Outbreak morbidity was 53%, with 9 of 14 horses culture positive and 26 of 53 horses qPCR positive for S. equi lacking clinical signs characteristic of strangles. By resolution, 91 of 112 had seroconverted to Antigen A by ELISA but seroconversion to antigen C (part of the SeM protein) was minimal. Sequencing of the isolates detected no alterations in the SeM protein, but identified a 61 bp deletion in the gene SEQ_0402. Conclusions: Absence of clinical signs alone in naïve horses may be an insufficient criterion to release horses from strangles quarantine measures. Restricted seroconversion to antigen C may have been associated with decreased clinical severity. The role of a minor gene deletion in SEQ_0402 in the virulence of S. equi warrants further investigation.
Copyright © 2018 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.
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Publication Date: 2018-01-30 PubMed ID: 29377359PubMed Central: PMC5787152DOI: 10.1111/jvim.15037Google Scholar: Lookup
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  • 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 investigated why weanling horses exhibited unexpectedly mild symptoms during an outbreak of strangles, a disease caused by the bacterium Streptococcus equi ssp. equi. The study found that infected horses did not display distinct strangles symptoms but had reduced seroconversion to a certain antigen, suggesting this could play a role in lessening the disease’s severity.

Objective and Methodology

  • The research aimed to study the clinical, serologic, and microbiologic reasons for a mild severity of strangles in a group of immunologically naïve weanling horses during a natural outbreak.
  • The researchers took 112 warmblood weanling horses and conducted a prospective longitudinal observational study throughout the outbreak, starting from the index case and proceeding until the disease was resolved.
  • At the peak of the outbreak, all the horses were examined through deep nasal swabs for the presence of S. equi. This was confirmed by the culture method and quantitative Polymerase Chain Reaction (PCR).
  • The horses were also examined clinically and serologically, using an optimized Enzyme-Linked Immunosorbent Assay (ELISA) to determine their immune response and seroconversion.
  • Analysis of data was done using descriptive statistics and the Wilcoxon signed-rank test.

Key Findings

  • The results showed that 53% of the cohort showed signs of the disease, with 9 of 14 horses being culture positive and 26 of 53 horses being qPCR positive for S. equi without showing signs typical of strangles.
  • By the end of the outbreak, 91 out of 112 horses had seroconverted to Antigen A —they had developed an immune response against this antigen— as determined by the ELISA.
  • Interestingly, there was minimal seroconversion to antigen C, another important part of the SeM protein of S. equi.
  • The sequenced isolates had no changes in the SeM protein. However, they did find a 61 base pair deletion in the gene SEQ_0402.

Conclusions

  • The results led to the conclusion that the absence of clinical signs alone in naïve horses might not conclusively signify the end of a strangles infection and thus, releasing them from quarantine based solely on this criterion may not be sufficient.
  • The restricted seroconversion to antigen C was thought to potentially associate with the decreased clinical severity of the disease seen in the cohort. Further studies are needed to confirm this relationship.
  • The researchers also believe the deletion in the gene SEQ_0402 might impact the virulence of S. equi, a hypothesis that warrants additional investigation.

Cite This Article

APA
Tscheschlok L, Venner M, Steward K, Böse R, Riihimäki M, Pringle J. (2018). Decreased Clinical Severity of Strangles in Weanlings Associated with Restricted Seroconversion to Optimized Streptococcus equi ssp equi Assays. J Vet Intern Med, 32(1), 459-464. https://doi.org/10.1111/jvim.15037

Publication

Journal of veterinary internal medicine
ISSN: 1939-1676
NlmUniqueID: 8708660
Country: United States
Language: English
Volume: 32
Issue: 1
Pages: 459-464

Researcher Affiliations

Tscheschlok, L
  • Equine Veterinary Clinic, Destedt, Germany.
Venner, M
  • Equine Veterinary Clinic, Destedt, Germany.
Steward, K
  • Department of Bacteriology, Animal Health Trust, Newmarket, UK.
Böse, R
  • Labor Dr. Böse GmbH, Harsum, Germany.
Riihimäki, M
  • Swedish University of Agricultural Sciences, Uppsala, Sweden.
Pringle, J
  • Swedish University of Agricultural Sciences, Uppsala, Sweden.

MeSH Terms

  • Animals
  • Disease Outbreaks / veterinary
  • Enzyme-Linked Immunosorbent Assay / veterinary
  • Female
  • Horse Diseases / immunology
  • Horse Diseases / microbiology
  • Horses
  • Male
  • Nasal Cavity / microbiology
  • Polymerase Chain Reaction / veterinary
  • Prospective Studies
  • Seroconversion
  • Streptococcal Infections / immunology
  • Streptococcal Infections / microbiology
  • Streptococcal Infections / veterinary
  • Streptococcus equi / genetics
  • Streptococcus equi / immunology
  • Streptococcus equi / isolation & purification

Conflict of Interest Statement

Authors declare no conflict of interest.

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This article has been cited 12 times.
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