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Abstract

Background Strangles, caused by Streptococcus equi subspecies equi (S. equi), is a prevalent infectious disease of horses. This is the first report on the use of a new vaccine, Strangvac, in a natural outbreak of strangles. Objectives To measure the effects of Strangvac vaccination during an outbreak of strangles at a Swedish farm. Study Design Longitudinal cohort study. Methods Healthy horses (n = 17) were vaccinated on day 0, which occurred 23 days after strangles was first confirmed in three unvaccinated horses on the same farm. Blood serum samples were collected on day 0, day 28 and day 489. A combined iELISA was used to measure total antibody titres towards the components of the vaccine. Specific antibody levels in blood sera to S. equi were also quantified using the antigen A/C iELISAs, which can differentiate infected from vaccinated animals. Clinical signs were monitored. Results All vaccinated horses had increased total antibody titres to CCE, Eq85 and/or IdeE from day 0 (2.50 +/- 0.28) to day 28 (3.63 +/- 0.31; p < 0.0001). Seropositivity in the antigen A/C iELISA was noted in 8/17 healthy horses on day 0 (prior to vaccination), in 9/16 vaccinates on day 28, and in 3/3 unvaccinated clinical cases on day 28. None of the vaccinated horses developed strangles, but 5/7 of the original vaccinated horses tested seropositive in the A/C iELISA on day 489, which was 377 days after their third vaccination. Main Limitations Aside from the three unvaccinated clinical cases, no unvaccinated control group was available. Conclusions Despite adherence to recommended biosecurity measures, serological evidence of exposure to S. equi was demonstrated in half of the vaccinated horses. Notably, all horses vaccinated during the outbreak responded to the vaccine components and remained healthy, suggesting a protective effect of vaccination of healthy horses with Strangvac in outbreak situations.

Keywords

horse; outbreak; strangles; Strangvac; Streptococcus equi; vaccine

Published in

Equine Veterinary Journal
2025
Publisher: WILEY

SLU Authors

UKÄ Subject classification

Pathobiology

Publication identifier

  • DOI: https://doi.org/10.1111/evj.70125

Permanent link to this page (URI)

https://res.slu.se/id/publ/144978