Markers of long term silent carriers of Streptococcus equi ssp. equi in horses.
Abstract: Difficulty in detection of silent carriers of Streptococcus equi is a key reason for its continued spread to immunologically naïve groups of horses. Objective: To determine whether clinical examination, markers of inflammation, or serology differentiate silent carriers of S. equi in recovered comingled horses. Methods: Ninety-eight warmblood yearlings and 72 unaffected mares on a large breeding farm (outbreak A), 38 mature Icelandic horses at a riding stable (outbreak B), and 27 mixed breed horses at a boarding stable (outbreak C). Methods: Prospective observational study 6 months to 2 years after strangles outbreaks. Carriers were defined as any animal positive on culture or qPCR to S. equi from nasopharyngeal lavage or guttural pouch endoscopy and lavage. Most horses had complete physical exams and 1 group included evaluation of white blood cell counts and serum amyloid A. Sera from all horses was tested for antibodies to antigens A and C of S. equi using an enhanced indirect ELISA. Descriptive statistics were calculated. Data were compared using paired t tests, Wilcoxon ranked test, chi square, or the Fishers exact test. Significance was set at P < .05. Results: Apart from weanlings at 6 months in outbreak A, there was no significant association between any clinical markers or serology with carrier state (P = .06-1). Moreover, 3/12 culture positive carriers were seronegative to S. equi. Conclusions: Silent carriers of S. equi do not differ clinically or on markers of inflammation to their noncarrier herd-mates. Moreover, serology alone will not distinguish carriers in comingled horses.
© 2020 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.
Publication Date: 2020-10-19 PubMed ID: 33074578PubMed Central: PMC7694814DOI: 10.1111/jvim.15939Google Scholar: Lookup
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- Journal Article
- Observational Study
- Veterinary
- Antibodies
- Asymptomatic Carriers
- Clinical Examination
- Diagnostic Technique
- Disease Outbreaks
- Enzyme-Linked Immunosorbent Assay (ELISA)
- Epidemiology
- Equine Health
- Guttural Pouch
- Herd Management
- Horse Breeds
- Icelandic Horses
- Immunology
- Infectious Disease
- Inflammatory Response
- Pharynx
- Serology
- Streptococcus
- Warmblood Horses
Summary
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The research explores the identification of ‘silent carriers’ of Streptococcus equi in horses, confirming that routine checks including physical exams and serology testing fail to effectively differentiate carriers from non-carriers.
Objective
- The aim of this study is to decipher whether clinical examination, markers of inflammation or serology could differentiate the ‘silent carriers’ of S. equi in recovered commingled horses. Silent carriers refer to the horses which carry the bacteria without showing apparent symptoms, thereby contributing to the transmission of the disease.
Methods
- The study population consisted of horses from three different stables, exposed to strangles outbreaks. Horses were analyzed after a span of six months to two years post-exposure.
- ‘Carriers’ were defined as the horses tested positive for S. equi from nasopharyngeal lavage or guttural pouch endoscopy and lavage.
- Horses underwent a thorough physical examination. In some cases, investigators assessed white blood cell counts and checked for the presence of an acute phase protein, serum amyloid A.
- Serum from all horses was tested for the presence of antibodies to antigens A and C of S. equi using an advanced indirect ELISA method.
- Descriptive statistics were calculated. The data obtained were compared using various statistical tests. Significance was set at P < .05.
Results
- Results showed no significant relationship between any clinical markers or serology results with the carrier state, except for weanlings at six months in outbreak A.
- Moreover, even among culture positive carriers, three were found to be seronegative to S. equi, making serology an unreliable method for identifying silent carriers.
Conclusions
- The researchers concluded that silent carriers of S. equi do not exhibit noticeable differences, either clinically or on markers of inflammation, from their non-carrier peers. Furthermore, solely relying on serology doesn’t suffice to spot carriers among commingled horses.
Cite This Article
APA
Pringle J, Venner M, Tscheschlok L, Waller AS, Riihimäki M.
(2020).
Markers of long term silent carriers of Streptococcus equi ssp. equi in horses.
J Vet Intern Med, 34(6), 2751-2757.
https://doi.org/10.1111/jvim.15939 Publication
Researcher Affiliations
- Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
- Equine Veterinary Clinic, Destedt, Germany.
- Equine Veterinary Clinic, Destedt, Germany.
- Animal Health Trust, Suffolk, UK.
- Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
MeSH Terms
- Animals
- Biomarkers
- Carrier State / veterinary
- Female
- Horse Diseases / diagnosis
- Horses
- Streptococcal Infections / diagnosis
- Streptococcal Infections / veterinary
- Streptococcus equi
Grant Funding
- 221-2013-606 / Svenska Forskningsrådet Formas
Conflict of Interest Statement
Andrew Waller through his employment at the Animal Health Trust has an economic interest in marketing the iELISA against S. equi. No other authors have any conflict of interest.
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This article includes 17 references
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Citations
This article has been cited 6 times.- Rask E, Righetti F, Ruiz A, Bjerketorp J, Frosth S, Frykberg L, Jacobsson K, Guss B, Flock JI, Henriques-Normark B, Hartman E, Gustafsson A, Paillot R, Waller AS. Closing the Stable Door on Strangles: Serological Responses of Vaccinated Horses on a Farm Following the Arrival of a New Horse. Animals (Basel) 2025 Dec 13;15(24).
- Gröndahl G, Righetti F, Aspán A, Bjerketorp J, Frosth S, Frykberg L, Jacobsson K, Guss B, Paillot R, Flock JI, Henriques-Normark B, Waller AS. Reining in strangles: Absence of disease in horses vaccinated with a DIVA-compatible recombinant fusion protein vaccine, Strangvac, following natural exposure to Streptococcus equi subspecies equi. Equine Vet J 2026 Mar;58(2):476-485.
- McLinden LA, Kemp-Symonds JG, Daly JM, Blanchard AM, Waller AS, Freeman SL. Effectiveness of a screening protocol employed at a UK rescue centre to prevent introduction of strangles. Equine Vet J 2026 Mar;58(2):466-475.
- Jaramillo-Morales C, James K, Barnum S, Vaala W, Chappell DE, Schneider C, Craig B, Bain F, Barnett DC, Gaughan E, Pusterla N. Voluntary Biosurveillance of Streptococcus equi Subsp. equi in Nasal Secretions of 9409 Equids with Upper Airway Infection in the USA. Vet Sci 2023 Jan 20;10(2).
- Rotinsulu DA, Ewers C, Kerner K, Amrozi A, Soejoedono RD, Semmler T, Bauerfeind R. Molecular Features and Antimicrobial Susceptibilities of Streptococcus equi ssp. equi Isolates from Strangles Cases in Indonesia. Vet Sci 2023 Jan 10;10(1).
- Pringle J, Aspán A, Riihimäki M. Repeated nasopharyngeal lavage predicts freedom from silent carriage of Streptococcus equi after a strangles outbreak. J Vet Intern Med 2022 Mar;36(2):787-791.
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