Good antimicrobial stewardship essential to protect their ongoing use in horses – review

Careful management of antibiotic use will ensure these crucial drugs remain effective in treating horses for generations to come. Photo: File
Careful management of antibiotic use will ensure these crucial drugs remain effective in treating horses for generations to come. Photo: File

Responsible antibiotic use in horses is essential so that they will remain effective in the future, a researcher says.

“The growing problem of antimicrobial resistance affects veterinarians on a daily basis,” says Cajsa Isgren, a senior lecturer in equine surgery with the University of Liverpool. “Antimicrobial stewardship and responsible prescribing are essential for a future with effective antimicrobials, as it is unlikely that new antimicrobials will become available for use in horses in the near future.”

Isgren, in a review just published in the journal Equine Veterinary Education, explored antimicrobial use in horses.

Antimicrobial resistance is a global problem, she said, which unfortunately remains an ongoing challenge in both human and veterinary medicine.

“Horses occupy a unique niche globally in that they, as companion animals, frequently have direct contact with humans, as well as indirect contact through contamination of walking trails or other public spaces with horse faeces or through the use of horse faeces to fertilise crops for human consumption.

“In addition, many horses have a high financial value and in some countries, have the potential to enter the food chain in meat products.

“These diverse aspects of the role of horses in society mean that increased antimicrobial resistance in horses is likely to have economic, emotional and public health implications.”

Antimicrobial resistance in horses is expected to become an increasing concern to clinicians over time, she said, given the lack of new antimicrobials on the horizon for horses.

She listed extended-spectrum β-lactamase-producing Enterobacteriaceae, methicillin-resistant Staphylococcus aureus (MRSA) and Salmonella species as pathogens of significant concern.

But there are also other opportunistic pathogens, including species of Pseudomonas, α-haemolytic Streptococcus, Enterococcus, and Acinetobacter, which have limited treatment options in adult horses because of their high intrinsic resistance.

“It is essential that highest priority, critically important antimicrobials such as ceftiofur, enrofloxacin, rifampicin and polymyxin B are used prudently in horses and ideally based on culture and antimicrobial susceptibility testing.”

Isgren noted that serum procalcitonin levels are used in humans to distinguish noninfectious inflammatory conditions from inflammation caused by bacteria and other infectious agents, and are also used as a guide for when to end antimicrobial treatment.

“Although no such studies have been performed in horses, this or other markers may prove to be helpful in guiding antimicrobial treatment decisions in the future,” she said.

“Optimising sampling techniques and good communication with the microbiology laboratory are essential for generating the accurate culture and antimicrobial susceptibility test results that underpin appropriate antimicrobial use,” she said.

“Additionally, there is clearly a need for national and international harmonisation of laboratory methods in order to improve the reliability and consistency of results reported by different laboratories.”

Isgren said evidence from sales data indicated that Britain’s veterinarians were using fewer antimicrobials year on year, and are meeting or even exceeding targets for reduced antimicrobial use.

“The equine veterinary profession is in a better position now compared with a decade ago with regard to antimicrobial stewardship as there is increased awareness of responsible prescribing.”

This, she said, has been achieved through education, action by scientific publications, and improved financial support from funding bodies for research into antimicrobial resistance in horses.

“However, the work does not end here. Future studies should investigate other ways of improving responsible antimicrobial prescribing by equine veterinarians including exploring behavioural drivers behind antimicrobial prescriptions and barriers to culture and antimicrobial susceptibility testing.

“Increased awareness and understanding of antimicrobial stewardship is required to tackle this complicated global issue and to protect antimicrobials so that they will remain effective in horses in the future.”

Improving clinical outcomes via responsible antimicrobial use in horses, C. M. Isgren. Equine Veterinary Education, 03 June 2021

The review, published under a Creative Commons License, can be read here

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