Injection site abscesses associated with commensal and environmental bacteria following intramuscular vaccination in horses.
Abstract: Five previously healthy horses in Korea, including a 19-year-old mixed-breed gelding, a 16-year-old mixed-breed mare, a 13-year-old Thoroughbred gelding, a 12-year-old Belgian warmblood mare, and a 12-year-old Andalusian mare, developed subcutaneous abscesses in the left neck after receiving intramuscular vaccination without prior skin disinfection. The vaccination used was Equivac® 2 in1, containing toxoid and cell-free extract. Within one week, the horses developed localised swelling and/or abscessation at the injection site. One case involved a ruptured abscess, while the others presented with warm, mildly painful, and non-fluctuant swellings. No foreign bodies were palpable at the injection sites. Both aerobic and anaerobic bacterial cultures were performed using 5 % defibrinated sheep blood agar, and the isolates were identified as and , all of which were consistent with commensal or environmental flora. PCR testing was negative for . In this cohort, post-injection abscesses occurred in 5 out of 70 horses (7.1 %) and were associated with commensal and environmental bacterial species, suggesting these cases likely resulted from procedural lapses rather than a direct vaccine-related reaction. Although the benefit of alcohol swabbing is debated in human medicine, this practice may offer important benefits under variable hygienic conditions in equine field settings. Accordingly, disinfecting the injection site with an alcohol- or disinfectant-soaked swab should be considered a routine precaution to minimise post-injection complications in horses.
© 2025 The Authors. Published by Elsevier Ltd.
Publication Date: 2025-07-25 PubMed ID: 40791848PubMed Central: PMC12336836DOI: 10.1016/j.vas.2025.100484Google Scholar: Lookup
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Summary
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This research found that five horses in Korea developed abscesses at the injection site after receiving a vaccine, likely due to a lack of skin disinfection before the injection. The study suggests that the practice of swabbing the injection site with alcohol or disinfectant could reduce post-injection complications in horses.
Introduction
- This research focused on five previously healthy horses in Korea that developed subcutaneous abscesses in the left neck after having Equivac® 2 in 1 vaccine, without prior skin disinfection.
- The horses included a 19-year-old mixed-breed gelding, a 16-year-old mixed-breed mare, a 13-year-old thoroughbred gelding, a 12-year-old Belgian warmblood mare, and a 12-year-old Andalusian mare.
- An abscess is a localized collection of pus that generally develops in response to a bacterial infection.
Development of Abscesses and Bacterial Culture
- One week after the vaccination, each of the five horses developed localised swelling and/or abscessation at the injection site.
- One horse ended up with a ruptured abscess, while the others presented with warm, mildly painful, and non-fluctuant swellings, with no foreign bodies palpable at the injection sites.
- Scientists performed both aerobic and anaerobic bacterial cultures using defibrinated sheep blood agar to identify the bacteria present in the abscesses.
- The bacteria identified were consistent with commensal or environmental flora, pointing out that post-injection abscesses likely resulted from procedural lapses rather than a direct vaccine-related reaction.
PCR Testing
- Additionally, PCR testing was conducted, which was negative for . This further suggests that the abscesses were not caused by a reaction to the vaccine but were more likely a result of the injection procedure.
Overall Findings
- In this study, the horses that developed post-injection abscesses represented 7.1% of the total cohort of 70 horses.
- The researchers concluded that the post-injection abscesses were likely associated with commensal and environmental bacterial species due to a lack of proper disinfection prior to the vaccination.
- The study suggests that even though the benefit of alcohol swabbing is a matter of debate in human medicine, it could potentially provide important benefits in equine field settings.
Recommendations
- Based on the study’s findings, it is recommended to disinfect the injection site with an alcohol- or disinfectant-soaked swab as a routine precaution to minimise post-injection complications in horses.
Cite This Article
APA
Ryu SH, Forbes E, Kim BS, Park KT.
(2025).
Injection site abscesses associated with commensal and environmental bacteria following intramuscular vaccination in horses.
Vet Anim Sci, 29, 100484.
https://doi.org/10.1016/j.vas.2025.100484 Publication
Researcher Affiliations
- Department of Equine Resources Science, Cheju Halla University, Jeju, 63092, South Korea.
- Racing Integrity Board, Private Bag 17902, Greenlane, Auckland, 1546, New Zealand.
- Department of Equine Science, Cheju Halla University, Jeju, 63092, South Korea.
- Department of Biological Science, Inje University, Gimhae, 50834, South Korea.
Conflict of Interest Statement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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