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Home / Equine Research Bank / Animals (Basel) / Closing the Stable Door on Strangles: Serological Responses ...
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.
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Publication Date: 2025-12-13 PubMed ID: 41463869PubMed Central: PMC12729937DOI: 10.3390/ani15243584Google Scholar: Lookup
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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.

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