Long term silent carriers of Streptococcus equi ssp. equi following strangles; carrier detection related to sampling site of collection and culture versus qPCR.
Abstract: After strangles outbreaks, Streptococcus equi ssp. equi (S. equi) can persist in clinically normal silent carriers for months to years. Two naturally occurring outbreaks of strangles with 53 and 100% morbidity, respectively, were followed longitudinally to assess occurrence of carrier state and optimal detection methods Outbreak A involved 98 yearling warmbloods, and outbreak B 38 mature Icelandic horses. Fully recovered horses were sampled at least 6 months after index cases using nasal swabs (one sampling occasion only) nasopharyngeal lavage and guttural pouch visualisation and lavages for culture and qPCR to S. equi. Any horse with at least a single sample positive was deemed a carrier. Descriptive statistics and sensitivity and negative predictive values were calculated. Comparisons were made with McNemars and Fishers exact tests. Carrier rates in outbreak A were 3% based on culture and 15% based on qPCR and for outbreak B 13% based on culture and 37% based on qPCR. All culture positives were also qPCR positive. One carrier culture negative sampled after an additional 8 months was culture positive to S. equi, indicating that qPCR positives should be suspected to carry live bacteria. Findings indicate that reliance on guttural pouch sampling and appearance does not capture all silent carriers. All culture positives were identified by qPCR and even horses positive by qPCR but culture negative should be suspected carriers of live bacteria.
Copyright © 2019 Elsevier Ltd. All rights reserved.
Publication Date: 2019-02-11 PubMed ID: 30902191DOI: 10.1016/j.tvjl.2019.02.003Google Scholar: Lookup
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- Journal Article
- Asymptomatic Carriers
- Diagnosis
- Diagnostic Technique
- Disease Diagnosis
- Disease Management
- Disease Outbreaks
- Disease Transmission
- Epidemiology
- Equine Diseases
- Equine Health
- Horses
- Icelandic Horses
- Infection
- Infectious Disease
- Longitudinal Study
- Microbiology
- Pathogens
- Polymerase Chain Reaction
- Strangles
- Streptococcus
- Veterinary Medicine
Summary
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This research investigates the occurrence of long-term silent carriers of Streptococcus equi ssp. equi (S. equi), a bacterium causing strangles in horses, after outbreaks and the efficiency of different detection methods. The results showed that a significant number of horses continued to carry the bacteria even after recovery, sometimes for several months, and qPCR was more sensitive in detecting these silent carriers compared to culture methods.
Introduction and Methods
- The study stemmed from the fact that S. equi, the bacteria that causes strangles in horses, can stay in seemingly healthy carriers for months or even years following an outbreak.
- Two outbreaks of strangles, one amongst 98 yearling warmblood horses (outbreak A) and the other amongst 38 mature Icelandic horses (outbreak B) were studied longitudinally to assess the carrier state of the bacteria and the best methods to detect its presence.
- The horses, all of which had fully recovered, were sampled at least 6 months after the index cases using nasal swabs, nasopharyngeal lavage, and guttural pouch visualisation and lavages.
- Both culture and qPCR methods were used to detect S. equi in the samples.
Results
- According to culture methods, the carrier rates were found to be 3% in outbreak A and 13% in outbreak B.
- The qPCR method, however, displayed significantly higher carrier rates – 15% in outbreak A and 37% in outbreak B.
- All culture positive samples also tested positive by qPCR, but not necessarily vice versa, indicating that qPCR was a more sensitive method of detection.
- Even a horse that tested negative by culture but positive by qPCR later tested positive by culture, suggesting that qPCR can detect silent carriers that might be missed by culture methods.
- These findings support the requirement of not relying solely on sampling and appearance of guttural pouch for identifying silent carriers.
Conclusion
- The results from this research imply that there may be a significant number of silent carriers of S. equi following a strangles outbreak.
- The use of qPCR method for detection of S. equi in suspected carriers is recommended, due to its higher sensitivity compared to culture methods.
- Even horses that test negative by culture but positive by qPCR should be suspected of carrying live bacteria, as culture methods may not be able to detect all silent carriers.
Cite This Article
APA
Pringle J, Venner M, Tscheschlok L, Bächi L, Riihimäki M.
(2019).
Long term silent carriers of Streptococcus equi ssp. equi following strangles; carrier detection related to sampling site of collection and culture versus qPCR.
Vet J, 246, 66-70.
https://doi.org/10.1016/j.tvjl.2019.02.003 Publication
Researcher Affiliations
- Swedish University of Agricultural Sciences, Department of Clinical Sciences, Box 7054, 750 07 Uppsala, Sweden. Electronic address: john.pringle@slu.se.
- Equine Veterinary Clinic, Destedt, Germany.
- Equine Veterinary Clinic, Destedt, Germany.
- Swedish University of Agricultural Sciences, Department of Clinical Sciences, Box 7054, 750 07 Uppsala, Sweden.
- Swedish University of Agricultural Sciences, Department of Clinical Sciences, Box 7054, 750 07 Uppsala, Sweden.
MeSH Terms
- Animals
- Carrier State / diagnosis
- Carrier State / epidemiology
- Carrier State / veterinary
- Disease Outbreaks / veterinary
- Ear, Middle / microbiology
- Female
- Horse Diseases / diagnosis
- Horse Diseases / microbiology
- Horses
- Longitudinal Studies
- Male
- Nasal Lavage / veterinary
- Real-Time Polymerase Chain Reaction / veterinary
- Streptococcal Infections / diagnosis
- Streptococcal Infections / epidemiology
- Streptococcal Infections / veterinary
- Streptococcus equi / growth & development
- Streptococcus equi / isolation & purification
Citations
This article has been cited 11 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).
- 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.
- Veiga RF, Clarindo LN, Fensterseifer AL, Pompelli LH, Sfaciotte RAP, Schwarz DGG, Eloy LR, Ferraz SM. Prevalence and antimicrobial susceptibility of Streptococcus equi isolated from horses in Santa Catarina state, Southern Brazil. Braz J Microbiol 2024 Dec;55(4):4147-4155.
- Zu H, Sun R, Li J, Guo X, Wang M, Guo W, Wang X. Development of a Real-Time Recombinase-Aided Amplification Method for the Rapid Detection of Streptococcus equi subsp. equi. Microorganisms 2024 Apr 11;12(4).
- Weese JS, Saab M, Moore A, Cai H, McClure JT. Relationship between quantitative real-time PCR cycle threshold and culture for detection of Streptococcus equi subspecies equi. Can Vet J 2023 Jun;64(6):549-552.
- Nadruz V, Beard LA, Delph-Miller KM, Larson RL, Bai J, Chengappa MM. Efficacy of high-level disinfection of endoscopes contaminated with Streptococcus equi subspecies equi with 2 different disinfectants. J Vet Intern Med 2023 Jul-Aug;37(4):1561-1567.
- 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.
- Brankston G, Rossi TM, O'Sullivan TL, Greer AL. Diagnostic testing patterns for Streptococcus equi subsp. equi in Ontario horses during the years 2008 to 2018. Can Vet J 2021 Jun;62(6):629-636.
- Morris ERA, Boyle AG, Riihimäki M, Aspán A, Anis E, Hillhouse AE, Ivanov I, Bordin AI, Pringle J, Cohen ND. Differences in the genome, methylome, and transcriptome do not differentiate isolates of Streptococcus equi subsp. equi from horses with acute clinical signs from isolates of inapparent carriers. PLoS One 2021;16(6):e0252804.
- Pringle J, Venner M, Tscheschlok L, Waller AS, Riihimäki M. Markers of long term silent carriers of Streptococcus equi ssp. equi in horses. J Vet Intern Med 2020 Nov;34(6):2751-2757.
- Pringle J, Storm E, Waller A, Riihimäki M. Influence of penicillin treatment of horses with strangles on seropositivity to Streptococcus equi ssp. equi-specific antibodies. J Vet Intern Med 2020 Jan;34(1):294-299.
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