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BMC veterinary research2025; 21(1); 558; doi: 10.1186/s12917-025-05011-4

Analysis of the presence of Beta-hemolytic streptococci and cytological profiles in horse tracheal lavage samples with diverse clinical respiratory symptoms.

Abstract: Riding clubs face significant financial losses due to upper respiratory infections caused by Beta-hemolytic (β-hemolytic) streptococci, leading to strangles and related diseases that negatively impact the health and performance of horses. Our objective was to determine the relationship between these inflammatory cells, the presence of β-hemolytic streptococcal species, and the clinical symptoms exhibited by the horses. This study investigated the presence of β-hemolytic streptococcus in 133 tracheal lavage samples from horses exhibiting various clinical respiratory symptoms and quantified the populations of neutrophils, eosinophils, macrophages, lymphocytes, and mast cells. The horses included in this study exhibited a variety of clinical respiratory symptoms categorized into groups: (I) Horses with no apperent symptoms (Control Group), (II) Horses with only coughing, (III) Horses with only lymph node swelling, (IV) Horses with coughing and lymph node swelling, (V) Horses with all symptoms (coughing, lymph node swelling and nasal discharge). After obtaining the bacterial cultures from tracheal wash samples, additional diagnostic tests were performed to identify the suspected colonies. The cytological analysis determined the proportions of inflammatory cells, while the statistical analysis assessed the significance of differences in inflammatory cell populations and pathogen presence across the different symptom groups. Results: Among 133 horses categorized into five clinical groups, S. zooepidemicus was isolated in 18% overall, with the highest isolation rate in horses exhibiting both coughing and lymph node swelling (36%). Statistical analysis showed a significant difference in S. zooepidemicus prevalence between groups (p = 0.019), with post hoc tests confirming significance between asymptomatic horses and those with combined symptoms. Neutrophil proportions differed significantly among groups (p = 0.010), with the highest counts in symptomatic horses with both coughing and lymph node swelling. Furthermore, bacteriologically positive samples exhibited significantly higher neutrophil counts (median 83.5, IQR 76) than negatives (median 22, IQR 46, p < 0.001), suggesting an acute inflammatory response linked to infection. In contrast, macrophage, lymphocyte, and eosinophil counts showed no significant variation among groups or infection status. Conclusions: Horses with coughing and lymph node swelling showed the highest prevalence of β-hemolytic streptococci. S. zooepidemicus infection was associated with increased neutrophils and decreased macrophages and lymphocytes, highlighting the role of neutrophils in inflammation. Asymptomatic horses may also carry the bacteria, indicating their role as carriers. Distinct inflammatory profiles correspond to clinical signs, underscoring the complexity of equine respiratory disease and the value of cytology and tracheal wash in diagnosis.
© 2025. The Author(s).
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Publication Date: 2025-10-02 PubMed ID: 41039541PubMed Central: PMC12492701DOI: 10.1186/s12917-025-05011-4Google Scholar: Lookup
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Summary

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Research Overview

  • This study examined the relationship between Beta-hemolytic streptococci infection, inflammatory cell populations in tracheal lavage samples, and clinical respiratory symptoms in horses.
  • It aimed to understand how bacterial presence correlates with different clinical signs and inflammatory responses in horses experiencing respiratory issues.

Background and Significance

  • Riding clubs often suffer financial losses due to respiratory infections in horses caused by Beta-hemolytic streptococci.
  • These infections can lead to diseases such as strangles, which severely impact horse health and performance.
  • Understanding the pathogen involvement and immune response helps improve diagnosis and treatment strategies.

Study Objective

  • The main goal was to investigate the connection between the presence of β-hemolytic streptococci, specifically S. zooepidemicus, inflammatory cell profiles in the tracheal lavage, and clinical symptoms observed in horses.
  • Assess how different respiratory symptoms correlate with bacterial infection and immune cell population changes.

Methodology

  • Samples: 133 tracheal lavage fluid samples collected from horses showing various clinical respiratory symptoms.
  • Clinical groups:
    • Group I: No apparent symptoms (Control)
    • Group II: Coughing only
    • Group III: Lymph node swelling only
    • Group IV: Coughing and lymph node swelling
    • Group V: Coughing, lymph node swelling, and nasal discharge
  • Bacterial cultures were conducted to isolate β-hemolytic streptococci.
  • Further diagnostic testing identified the bacterial species, focusing on S. zooepidemicus.
  • Cytological analysis quantified inflammatory cells: neutrophils, eosinophils, macrophages, lymphocytes, and mast cells.
  • Statistical analyses compared bacterial presence and inflammatory cell proportions across symptom groups.

Key Findings

  • Prevalence of S. zooepidemicus:
    • Overall isolation rate of 18% among all horses.
    • Highest prevalence (36%) observed in horses with both coughing and lymph node swelling.
    • Statistical significance observed in differences between groups (p = 0.019), particularly between asymptomatic horses and those with combined symptoms.
  • Inflammatory Cell Profiles:
    • Neutrophil proportions were significantly higher in symptomatic groups, especially those with combined symptoms (p = 0.010).
    • Bacteriologically positive samples had much higher neutrophil counts (median 83.5 with interquartile range 76) compared to negative samples (median 22, IQR 46), indicating an acute inflammatory response (p < 0.001).
    • Macrophage, lymphocyte, and eosinophil counts did not show significant variation among different groups or infection status.

Conclusions

  • Horses showing both coughing and lymph node swelling exhibited the greatest presence of β-hemolytic streptococci, especially S. zooepidemicus.
  • Infection with S. zooepidemicus is linked to increased neutrophil counts, suggesting neutrophils play a critical role in the inflammatory response to this pathogen.
  • Decreased macrophage and lymphocyte levels in infected horses indicate a shift in inflammatory cell composition during infection.
  • Some asymptomatic horses also carried the bacteria, implying they can act as asymptomatic carriers and potentially spread disease.
  • Distinct inflammatory cell patterns correspond to specific clinical signs, highlighting the complexity of equine respiratory diseases.
  • Cytology and tracheal lavage techniques are valuable diagnostic tools for assessing respiratory infections and inflammation in horses.

Cite This Article

APA
Pınar O, Çelik Doğan C, Aktaran Bala D, Kumaş C, Mete A. (2025). Analysis of the presence of Beta-hemolytic streptococci and cytological profiles in horse tracheal lavage samples with diverse clinical respiratory symptoms. BMC Vet Res, 21(1), 558. https://doi.org/10.1186/s12917-025-05011-4

Publication

BMC veterinary research
ISSN: 1746-6148
NlmUniqueID: 101249759
Country: England
Language: English
Volume: 21
Issue: 1
Pages: 558
PII: 558

Researcher Affiliations

Pınar, Orhan
  • Equine and Equine Training Program, Vocational School of Veterinary Medicine, Istanbul University-Cerrahpasa, Istanbul, 34320, Turkey.
Çelik Doğan, Cansu
  • Food Technology Program, Food Processing Department, Vocational School of Veterinary Medicine, Istanbul University-Cerrahpasa, Istanbul, 34320, Turkey. cansu.celik@iuc.edu.tr.
Aktaran Bala, Deniz
  • Food Technology Program, Food Processing Department, Vocational School of Veterinary Medicine, Istanbul University-Cerrahpasa, Istanbul, 34320, Turkey.
Kumaş, Cihan
  • Veliefendi Racecourse Horse Hospital, Jockey Club of Türkiye, İstanbul, 34144, Turkey.
Mete, Alper
  • Veliefendi Racecourse Horse Hospital, Jockey Club of Türkiye, İstanbul, 34144, Turkey.

MeSH Terms

  • Animals
  • Horses
  • Horse Diseases / microbiology
  • Horse Diseases / pathology
  • Streptococcal Infections / veterinary
  • Streptococcal Infections / microbiology
  • Streptococcal Infections / pathology
  • Streptococcus / isolation & purification
  • Respiratory Tract Infections / veterinary
  • Respiratory Tract Infections / microbiology
  • Respiratory Tract Infections / pathology
  • Male
  • Trachea / microbiology
  • Female

Conflict of Interest Statement

Declarations. Ethics approval: For the present study ethical approval was obtained from the Ethical Committee, Faculty of Veterinary Medicine, University of Selcuk (Number 2006–2006/079). Consent for publication: Not applicable. Prior publication: Data have not been published previously. Competing interests: The authors declare no competing interests.

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