The Horse

SEP 2018

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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38 THE HORSE September 2018 Smart Antibiotic Use Why is antimicrobial resistance such a big deal, and what can you do about it? DIANE RICE N one of us remembers living in a world without antimicrobial drugs. Yet, less than a century—a mere lifetime—ago, people and animals routinely died from conditions that today require no more than a tube of antibiotic ointment or a short course of antibiotics to cure. According to the Centers for Disease Control and Prevention (CDC), simply using antibiotics creates resistance. How? Antibiotic resistance is a complicated process that scientists do not fully understand. But, simply put, in any population of microbes, some naturally resist the drugs used to control or kill them. Then, when an infection arises and antimicrobials are used to kill disease- causing microbes, the commensal (good) mi- crobes that protect the body from infection also die. This leaves the drug-resistant microbes to proliferate unchecked. And, some bacteria pass their resistant genes to other bacteria, further spreading antibiotic resistance. In humans the CDC estimates that 2,049,442 illnesses and 23,000 deaths occurred due to antibiotic resistance in 2017 alone and, of these, 250,000 illnesses (12%) and 14,000 deaths (61%) were due to the bacterium Clostridium difficile. As far as microbes that affect both humans and horses, C. difficile ranks No. 1 among drug- resistant threats in the United States, with an "Urgent" CDC classification. On the CDC's "Serious" list are Salmonella and methi- cillin-resistant Staphylococcus aureus (MRSA). Erythromycin-resistant group A Streptococcus falls in the " Concerning" category. Also of concern is Escherichia coli and related bacteria (Enterobacteriaceae), says J. Scott Weese, DVM, DVSc, Dipl. ACVIM (LAIM), veterinary specialist at the University of Guelph, in Ontario, Canada, and a partner at the National Collaborating Cen- tre for Infectious Diseases. Wendy Vaala, VMD, Dipl. ACVIM, senior equine technical service veterinarian at Merck Animal Health, who's based in Alma, Wisconsin, says another bacterial species that has developed antimicrobial resistance (AMR) is Rhodococ- cus equi, which causes pneumonia complicated by abscess formation in young foals. "R. equi is frequently treated with one of two macrolide antibiotics—clarithromycin or azithromycin— and rifampin," she adds. "In recent years these antibiotics have been used with increasing frequency in foals suspected of having R. equi pneumonia. In many cases treatment is started prior to the onset of any clinical signs. As a result there has been an increasing number of reports of R. equi isolates that are resistant to these antibiotics." Indeed, antimicrobial-resistant infections of all kinds continue to challenge veterinarians and

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