FREE SHIPPING over $40
OVER 10000 FIVE-STAR REVIEWS
5% OFF ALL SUBSCRIPTIONS
100% HAPPINESS GUARANTEE
Analyze Diet
0
Animals : an open access journal from MDPI2025; 15(24); 3584; doi: 10.3390/ani15243584

Closing the Stable Door on Strangles: Serological Responses of Vaccinated Horses on a Farm Following the Arrival of a New Horse.

Abstract: Infection of susceptible horses with subspecies (), the causative agent of strangles, is associated with commingling. Exposure may occur among horses at equestrian events, sales, or horses moved among different equine stabling environments. Strangles can affect all horses on a farm, leading to the death of up to 10% of cases depending on their immunity status at the time of infection, the development of complications, the success of biosecurity measures, and the use of vaccination. The current retrospective study used ELISAs to measure the exposure of horses to at a farm that experienced an outbreak of strangles shortly after the introduction of a new horse on the same day that the majority of the 17 resident horses were vaccinated with Strangvac for the first time. One vaccinated horse, which subsequently tested positive for and EHV-4, developed a cough, elevated body temperature, and nasal discharge 11 days after the first vaccination. Two other horses developed fever for one day at 22 days post-first vaccination, but only one had serological evidence of exposure to . All vaccinated horses had high antibody titres to vaccine components, whilst 7 of the 17 resident horses, and the new arrival, tested seropositive for exposure to . Although 3 out of the 17 vaccinated horses developed mild signs of disease before second vaccination, serological data support the effectiveness of vaccination in resident populations of horses to minimise the risk of strangles following the introduction of a new horse.
Get Full Text
Publication Date: 2025-12-13 PubMed ID: 41463869PubMed Central: PMC12729937DOI: 10.3390/ani15243584Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
LinkedInCopy
  • 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.

Overview

  • This study evaluated immune responses and disease occurrence in vaccinated horses on a farm following the introduction of a new horse that coincided with an outbreak of strangles, a contagious equine respiratory disease.
  • The research focused on measuring serological (antibody) responses to determine infection exposure and assessed the effectiveness of vaccination in limiting disease spread.

Background on Strangles and Its Transmission

  • Strangles is caused by the bacterium Streptococcus equi subspecies equi, which primarily infects horses.
  • The disease spreads through close contact among horses, especially during:
    • Equestrian events
    • Horse sales
    • Movement between stabling environments
  • Strangles can severely affect a whole farm’s horse population, with up to 10% mortality depending on several factors such as:
    • Horses’ pre-existing immunity
    • Development of complications
    • Success of farm biosecurity measures
    • Use and timing of vaccination

Study Design and Methods

  • The study was retrospective, analyzing events that occurred on a particular horse farm.
  • Seventeen resident horses received their first dose of Strangvac, a vaccine targeting strangles, on the same day a new horse was introduced to the farm.
  • Researchers utilized ELISA (enzyme-linked immunosorbent assay) tests to measure antibody levels against Streptococcus equi, assessing:
    • Exposure to the bacteria
    • Immune response to the vaccine components

Findings on Disease Signs and Serological Responses

  • Clinical signs:
    • One vaccinated resident horse showed respiratory symptoms (cough, elevated temperature, nasal discharge) 11 days post-vaccination and tested positive for Streptococcus equi and equine herpesvirus (EHV-4).
    • Two other vaccinated horses developed a one-day fever around 22 days after first vaccination.
  • Serological results:
    • All vaccinated horses exhibited high antibody titres against vaccine components, indicating a strong immune response to the vaccine.
    • Seven of the 17 resident horses plus the newly introduced horse tested seropositive for exposure to Streptococcus equi, indicating natural infection or exposure.
    • Only one of the febrile horses had serological evidence confirming exposure to Streptococcus equi.

Interpretation and Implications

  • The study showed the occurrence of mild clinical signs in a small subset of vaccinated horses but overall highlighted a strong immune response to the vaccine.
  • Vaccination appeared effective in minimizing disease severity and spread despite the introduction of an exposed new horse.
  • Serological data suggest that vaccinating resident horses upon introduction of a new horse can enhance herd immunity and potentially reduce outbreaks of strangles.
  • Continued biosecurity and monitoring are important to control disease introduction and transmission on equine farms.

Conclusion

  • This research supports the use of the Strangvac vaccine as a valuable tool in controlling strangles in horse populations, especially during high-risk events such as the introduction of new animals.
  • Strategic vaccination, combined with appropriate management practices, can help “close the stable door” on potential strangles outbreaks.

Cite This Article

APA
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. (2025). Closing the Stable Door on Strangles: Serological Responses of Vaccinated Horses on a Farm Following the Arrival of a New Horse. Animals (Basel), 15(24), 3584. https://doi.org/10.3390/ani15243584

Publication

Animals : an open access journal from MDPI
ISSN: 2076-2615
NlmUniqueID: 101635614
Country: Switzerland
Language: English
Volume: 15
Issue: 24
PII: 3584

Researcher Affiliations

Rask, Erika
  • Veterinär Erika Rask AB, 442 32 Kungälv, Sweden.
Righetti, Francesco
  • Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, 171 77 Solna, Sweden.
Ruiz, Aymé
  • Mybac, 129 22 Stockholm, Sweden.
Bjerketorp, Joakim
  • Department of Animal Biosciences, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.
Frosth, Sara
  • Department of Animal Biosciences, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.
Frykberg, Lars
  • Department of Animal Biosciences, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.
Jacobsson, Karin
  • Department of Animal Biosciences, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.
Guss, Bengt
  • Department of Animal Biosciences, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.
Flock, Jan-Ingmar
  • Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, 171 77 Solna, Sweden.
Henriques-Normark, Birgitta
  • Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, 171 77 Solna, Sweden.
  • Clinical Microbiology, Karolinska University Hospital Solna, 171 76 Stockholm, Sweden.
Hartman, Emma
  • Intervacc AB, 129 22 Stockholm, Sweden.
Gustafsson, Agneta
  • Intervacc AB, 129 22 Stockholm, Sweden.
Paillot, Romain
  • Intervacc AB, 129 22 Stockholm, Sweden.
Waller, Andrew S
  • Intervacc AB, 129 22 Stockholm, Sweden.

Grant Funding

  • no grant number / Intervacc AB

Conflict of Interest Statement

E.R. reports no conflicts of interest. A.G., A.S.W., E.H., and R.P. are employed by Intervacc AB. A.R. is employed by Mybac, which is a subsidiary of Intervacc AB. B.G. and J.-I.F. are founders and former board members of Intervacc AB. F.R., J.B., S.F., L.F., K.J., and B.H.-N. have received research grants from Intervacc AB. None of the authors has any other financial or personal relationships that could inappropriately influence or bias the content of the paper. The analysis of serum samples was funded by Intervacc AB.

References

This article includes 41 references
  1. EIDS (Equine Infectious Diseases Surveillance) [(accessed on 22 September 2025)]. Available online: https://equinesurveillance.org/landing/
  2. International Collating Centre (ICC) [(accessed on 22 September 2025)]. Available online: https://equinesurveillance.org/iccview/
  3. van Maanen K, van den Wollenberg L, de Haan T, Frippiat T. Epidemiology of Infectious Pathogens in Horses with Acute Respiratory Disease, Abortion, and Neurological Signs: Insights Gained from the Veterinary Surveillance System for Horses in The Netherlands (SEIN). Vet. Sci. 2025;12:567.
    doi: 10.3390/vetsci12060567pmc: PMC12197731pubmed: 40559804google scholar: lookup
  4. Rendle D, Bowen M, Cavalleri J, De Brauwere N, Grondahl G, van Maanen K, Newton JR. Strangles Vaccination: A Current European Perspective. Equine Vet. Educ. 2025;37:90–97.
    doi: 10.1111/eve.14032google scholar: lookup
  5. Surveillance of Equine Strangles (SES) [(accessed on 24 September 2025)]. Available online: https://equinesurveillance.org/ses/
  6. 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;34:294–299.
    doi: 10.1111/jvim.15668pmc: PMC6979097pubmed: 31769122google scholar: lookup
  7. Boyle A. Streptococcus Equi Subspecies Equi Infection (Strangles) in Horses. Compend. Contin. Educ. Vet. 2011;33:E1–E7; quiz E8.
    pubmed: 21870348
  8. Jorm LR. Strangles in Horse Studs: Incidence, Risk Factors and Effect of Vaccination. Aust. Vet. J. 1990;67:436–439.
    doi: 10.1111/j.1751-0813.1990.tb03054.xpubmed: 2076065google scholar: lookup
  9. Boyle AG, Timoney JF, Newton JR, Hines MT, Waller AS, Buchanan BR. Streptococcus Equi Infections in Horses: Guidelines for Treatment, Control, and Prevention of Strangles-Revised Consensus Statement. J. Vet. Intern. Med. 2018;32:633–647.
    doi: 10.1111/jvim.15043pmc: PMC5867011pubmed: 29424487google scholar: lookup
  10. Christmann U, Pink C. Lessons Learned from a Strangles Outbreak on a Large Standardbred Farm. Equine Vet. Educ. 2017;29:138–143.
    doi: 10.1111/eve.12451google scholar: lookup
  11. Sweeney CR, Whitlock RH, Meirs DA, Whitehead SC, Barningham SO. Complications Associated with Streptococcus Equi Infection on a Horse Farm. J. Am. Vet. Med. Assoc. 1987;191:1446–1448.
    doi: 10.2460/javma.1987.191.11.1446pubmed: 3692991google scholar: lookup
  12. Osman S, Tharwat M, Saeed E. An Outbreak of Strangles in Arabian Horses in Saudi Arabia: Epidemiology, Clinical Signs and Treatment Outcomes. Int. J. Vet. Sci. 2021;10:323–328.
    doi: 10.47278/journal.ijvs/2021.061google scholar: lookup
  13. Newton JR, Wood JL, Dunn KA, DeBrauwere MN, Chanter N. Naturally Occurring Persistent and Asymptomatic Infection of the Guttural Pouches of Horses with Streptococcus Equi. Vet. Rec. 1997;140:84–90.
    doi: 10.1136/vr.140.4.84pubmed: 9032908google scholar: lookup
  14. Newton JR, Verheyen K, Talbot NC, Timoney JF, Wood JL, Lakhani KH, Chanter N. Control of Strangles Outbreaks by Isolation of Guttural Pouch Carriers Identified Using PCR and Culture of Streptococcus Equi. Equine Vet. J. 2000;32:515–526.
    doi: 10.2746/042516400777584721pubmed: 11093626google scholar: lookup
  15. Pringle J, Venner M, Tscheschlok L, Bächi L, Riihimäki M. 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. 2019;246:66–70.
    doi: 10.1016/j.tvjl.2019.02.003pubmed: 30902191google scholar: lookup
  16. Harris SR, Robinson C, Steward KF, Webb KS, Paillot R, Parkhill J, Holden MTG, Waller AS. Genome Specialization and Decay of the Strangles Pathogen, Streptococcus Equi, Is Driven by Persistent Infection. Genome Res. 2015;25:1360–1371.
    doi: 10.1101/gr.189803.115pmc: PMC4561494pubmed: 26160165google scholar: lookup
  17. 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. 2025. Online ahead of printing.
    doi: 10.1111/evj.14558pubmed: 40684376google scholar: lookup
  18. Timoney JF. Strangles. Vet. Clin. N. Am. Equine Pract. 1993;9:365–374.
    doi: 10.1016/S0749-0739(17)30403-0pubmed: 8358649google scholar: lookup
  19. Robinson C, Waller AS, Frykberg L, Flock M, Zachrisson O, Guss B, Flock J-I. Intramuscular Vaccination with Strangvac Is Safe and Induces Protection against Equine Strangles Caused by Streptococcus Equi. Vaccine 2020;38:4861–4868.
    doi: 10.1016/j.vaccine.2020.05.046pubmed: 32507408google scholar: lookup
  20. Robinson C, Steward KF, Potts N, Barker C, Hammond T, Pierce K, Gunnarsson E, Svansson V, Slater J, Newton JR. Combining Two Serological Assays Optimises Sensitivity and Specificity for the Identification of Streptococcus Equi Subsp. Equi Exposure. Vet. J. 2013;197:188–191.
    doi: 10.1016/j.tvjl.2013.01.033pubmed: 23465547google scholar: lookup
  21. Waller A, Flock M, Smith K, Robinson C, Mitchell Z, Karlström A, Lannergård J, Bergman R, Guss B, Flock J-I. Vaccination of Horses against Strangles Using Recombinant Antigens from Streptococcus Equi. Vaccine 2007;25:3629–3635.
    doi: 10.1016/j.vaccine.2007.01.060pubmed: 17321016google scholar: lookup
  22. Rosenthal JA. Qualitative Descriptors of Strength of Association and Effect Size. J. Soc. Serv. Res. 1996;21:37–59.
    doi: 10.1300/J079v21n04_02google scholar: lookup
  23. Boyle AG, Smith MA, Boston RC, Stefanovski D. A Case-Control Study Developing a Model for Predicting Risk Factors for High SeM-Specific Antibody Titers after Natural Outbreaks of Streptococcus Equi Subsp Equi Infection in Horses. J. Am. Vet. Med. Assoc. 2017;250:1432–1439.
    doi: 10.2460/javma.250.12.1432pubmed: 28569630google scholar: lookup
  24. 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;34:2751–2757.
    doi: 10.1111/jvim.15939pmc: PMC7694814pubmed: 33074578google scholar: lookup
  25. HBLB International Code of Practice 2025: Strangles—Prevention. [(accessed on 3 November 2025)]. Available online: https://codes.hblb.org.uk/index.php/page/103.
  26. Lakic B, Ekmann A, Lindahl J, Grondahl G. Streptococcus Equi Infections in Sweden Are Preceded by Introducing New Horses to the Premises. Equine Vet. J. 2024;56:15–16.
    doi: 10.1111/evj.14221google scholar: lookup
  27. Ryden A, Fernström L-L, Svonni E, Riihimäki M. Effectiveness of Cleaning and Sanitation of Stable Environment and Riding Equipment Following Contamination with Streptococcus Equi Subsp. Equi. J. Equine Vet. Sci. 2023;121:104204.
    doi: 10.1016/j.jevs.2022.104204pubmed: 36586522google scholar: lookup
  28. Weese JS, Jarlot C, Morley PS. Survival of Streptococcus Equi on Surfaces in an Outdoor Environment. Can. Vet. J. 2009;50:968–970.
    pmc: PMC2726026pubmed: 19949559
  29. Gröndahl G, Righetti F, Aspán A, Bjerketorp J, Frosth S, Frykberg L, Jacobsson K, Guss B, Paillot R, Flock J-I. 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. 2025. Online ahead of printing.
    doi: 10.1111/evj.70125pubmed: 41276995google scholar: lookup
  30. Reemers S, Sonnemans D, Horspool L, van Bommel S, Cao Q, van de Zande S. Determining Equine Influenza Virus Vaccine Efficacy—The Specific Contribution of Strain Versus Other Vaccine Attributes. Vaccines 2020;8:501.
    doi: 10.3390/vaccines8030501pmc: PMC7564743pubmed: 32899189google scholar: lookup
  31. Heldens JGM, Pouwels HGW, Derks CGG, Van de Zande SMA, Hoeijmakers MJH. The First Safe Inactivated Equine Influenza Vaccine Formulation Adjuvanted with ISCOM-Matrix That Closes the Immunity Gap. Vaccine 2009;27:5530–5537.
    doi: 10.1016/j.vaccine.2009.06.085pubmed: 19607950google scholar: lookup
  32. Wilson HJ, Dong J, van Tonder AJ, Ruis C, Lefrancq N, McGlennon A, Bustos C, Frosth S, Léon A, Blanchard AM. Progressive Evolution of Streptococcus Equi from Streptococcus Equi Subsp. Zooepidemicus and Adaption to Equine Hosts. Microb. Genom. 2025;11:001366.
    doi: 10.1099/mgen.0.001366pmc: PMC12453393pubmed: 40152912google scholar: lookup
  33. Tscheschlok L, Venner M, Steward K, Böse R, Riihimäki M, Pringle J. Decreased Clinical Severity of Strangles in Weanlings Associated with Restricted Seroconversion to Optimized Streptococcus Equi Ssp Equi Assays. J. Vet. Intern. Med. 2018;32:459–464.
    doi: 10.1111/jvim.15037pmc: PMC5787152pubmed: 29377359google scholar: lookup
  34. Kelly C, Bugg M, Robinson C, Mitchell Z, Davis-Poynter N, Newton JR, Jolley KA, Maiden MCJ, Waller AS. Sequence Variation of the SeM Gene of Streptococcus Equi Allows Discrimination of the Source of Strangles Outbreaks. J. Clin. Microbiol. 2006;44:480–486.
    doi: 10.1128/JCM.44.2.480-486.2006pmc: PMC1392674pubmed: 16455902google scholar: lookup
  35. Cursons R, Patty O, Steward KF, Waller AS. Strangles in Horses Can Be Caused by Vaccination with Pinnacle I. N.. Vaccine 2015;33:3440–3443.
    doi: 10.1016/j.vaccine.2015.05.009pubmed: 26025806google scholar: lookup
  36. Mitchell C, Steward KF, Charbonneau ARL, Walsh S, Wilson H, Timoney JF, Wernery U, Joseph M, Craig D, van Maanen K. Globetrotting Strangles: The Unbridled National and International Transmission of Streptococcus Equi between Horses. Microb. Genom. 2021;7:mgen000528.
    doi: 10.1099/mgen.0.000528pmc: PMC8190609pubmed: 33684029google scholar: lookup
  37. Ma G, Azab W, Osterrieder N. Equine Herpesviruses Type 1 (EHV-1) and 4 (EHV-4)--Masters of Co-Evolution and a Constant Threat to Equids and Beyond. Vet. Microbiol. 2013;167:123–134.
    doi: 10.1016/j.vetmic.2013.06.018pubmed: 23890672google scholar: lookup
  38. Jaramillo-Morales C, James K, Barnum S, Vaala W, Chappell DE, Schneider C, Craig B, Bain F, Barnett DC, Gaughan E. Voluntary Biosurveillance of Streptococcus equi subsp. Equi in Nasal Secretions of 9409 Equids with Upper Airway Infection in the USA. Vet. Sci. 2023;10:78.
    doi: 10.3390/vetsci10020078pmc: PMC9962190pubmed: 36851382google scholar: lookup
  39. Pavulraj S, Eschke K, Theisen J, Westhoff S, Reimers G, Andreotti S, Osterrieder N, Azab W. Equine Herpesvirus Type 4 (EHV-4) Outbreak in Germany: Virological, Serological, and Molecular Investigations. Pathogens 2021;10:810.
    doi: 10.3390/pathogens10070810pmc: PMC8308676pubmed: 34202127google scholar: lookup
  40. Righetti F, Hentrich K, Flock M, Frosth S, Jacobsson K, Bjerketorp J, Pathak A, Ido N, Henriques-Normark B, Frykberg L. Neutralisation of the Immunoglobulin-Cleaving Activity of Streptococcus Equi Subspecies Equi IdeE by Blood Sera from Ponies Vaccinated with a Multicomponent Protein Vaccine. Vaccines 2025;13:1061.
    doi: 10.3390/vaccines13101061pmc: PMC12568127pubmed: 41150447google scholar: lookup
  41. Rask E, Righetti F, Ruiz A, Bjerketorp J, Frosth S, Frykberg L, Jacobsson K, Guss B, Flock J-I, Henriques-Normark B. Serological Responses of Horses in Response to Vaccination in a Farm Associated with a Natural Outbreak of Strangles. Equine Vet. J. 12th International Equine Infectious Diseases Conference; Deauville, France. 30 September–4 October 2024; p. 20. S60.

Citations

This article has been cited 0 times.
Subscribe to our newsletter
Join 99,928 horse owners like you who receive our email updates on horse health and nutrition.