Over two million people are infected with an antibiotic-resistant bacteria every year, and close to 100,000 of them die. In fact, the World Health Organization has declared antibiotic resistance as one of the biggest threats to global health of current times. When antibiotics were introduced to medicine in the 1930s, they were hailed as miracle drugs. Formerly life-threatening illnesses could finally be cured with a simple pill, and by the 1960s, dozens of different antibiotics were developed to fight many serious diseases. Then, the bugs got smarter. 

Resistance to antibiotics began to develop as the bacteria targeted by an antibiotic found ways to overcome the medication’s effects. As the bacteria continue to get better and better at beating back these drugs, the risk that no antibiotic will be effective at curing an infection grows. To add to the concerns, there are very few “new” antibiotics being developed to take the place of those that are becoming less effective. It’s taken less than 100 years for the miracle of antibiotics to be threatened, and for the diseases, they once cured to become life-threatening once again.

So what does this have to do with you? We’ve all heard stories of the healthy young athlete who contracted an antibiotic-resistant infection after a routine surgery and ended up in the ICU. And we all probably think, Sure…but what are the chances that would happen to me? Those chances may be greater than you think. Would you be surprised to learn that equine vets, and the personnel who work alongside them, carry methicillin-resistant staph aureus (MRSA), one of the most well-known antibiotic-resistant superbugs of all, at significantly higher rates than the average population? In fact, MRSA is considered an “occupational hazard” for equine vets and their employees. There’s just no doubt about it—if you work with horses (or even if you don’t!) both you and your horse could be at risk for an antibiotic-resistant infection. 

In this article, we’ll learn a little bit about how antibiotic use in the horse world has contributed to this global health concern. We’ll discover what it takes to use antibiotics effectively and responsibly, and how you can play a part in helping to overcome health risks posed by antibiotic resistance.

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Too Much of a Good Thing?

Antibiotics save lives. That said, reaching for an antibiotic “just in case” is a terrible idea. In fact, one of the biggest contributors to the development of antibiotic resistance is overuse, and that’s exactly what we’re doing when we give an antibiotic that isn’t really needed. Rhodococcus equi, a bacteria that causes pneumonia in foals, provides a great example of antibiotic overuse gone wrong. 

Rhodococcus equi is an important cause of pneumonia on many breeding farms in the United States. It lives in the soil and foals are typically exposed at birth, with signs of pneumonia developing between the age of one and six months. This particular bacteria can be difficult to treat, requiring a combination of two different antibiotics, a macrolide (such as erythromycin) and rifampin. These are important antibiotics that are essential for treating certain types of infections—in both humans and animals. 

Some horse properties, most commonly large breeding farms, have cases of Rhodococcus equi pneumonia every year. This has led to the common practice of regularly screening foals using ultrasound to look for changes in the lungs consistent with possible infection. If abnormalities are seen, even if the foal isn’t sick (referred to as a “subclinical infection”), a macrolide antibiotic in combination with rifampin is prescribed in an effort to prevent pneumonia from developing. 

So what’s the problem? Resistance to macrolide antibiotics is rapidly developing—a problem for both horses and humans. In a recent study, macrolide-resistant Rhodococcus equi was identified on 76 of 100 Kentucky breeding farms. Unfortunately, other alternatives for effective treatment are limited. To make matters worse, studies show that the majority of foals with subclinical signs of pneumonia don’t get sick. By treating foals who were never likely to get sick, we’ve created resistance that limits treatment options for the ones that do.

The bottom line? We need to get better at determining when antibiotics are really needed and avoid the “just in case” approach. 

How Do You Decide?

Decisions about appropriate antibiotic use depends on several factors—including things you may not think about. It’s important to understand that antibiotics aren’t a “one size fits all” medication. In reality, an antibiotic that is effective against one type of bacteria may do nothing against another—compounded further if resistant bacteria are involved. Additionally, some antibiotics reach different parts of the body better than others. For example, an antibiotic that’s excreted in the urine might be great for a urinary tract infection, but have little or no ability to penetrate an abscess. 

Finally, antibiotics aren’t totally benign. They can cause toxicity to certain organs, or have side effects more deadly than the condition being treated in the first place. Did you know that trimethoprim-sulfamethoxazole (those “sulfa tabs” you likely reach for when your horse cuts his leg) can cause life-threatening colitis? Just think how you’d feel if your horse ended up in intensive care over a simple wound that was unlikely to become infected in the first place. All of these factors combine to make decision-making concerning antibiotic use more complicated than it seems.

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Your vet will take the following five steps when deciding about prescribing antibiotics for your horse: 

Step 1: Is It Bacterial? First and foremost, antibiotics will only be effective for a bacterial infection. That means that your horse with a fever or a snotty nose caused by a virus won’t benefit from starting antibiotics. Blood work can help determine whether the signs you are seeing are likely to be bacterial in origin, and is likely to be the first step your vet will recommend when deciding whether to pursue antibiotic treatment. 

Step 2: What Specific Organism Is Involved? The next step for determining appropriate treatment will be to collect a sample for a culture if it’s possible to do so. For that snotty nose, your vet may pass a swab into your horse’s nasal passage to submit to the lab, where they can grow the bacteria and attempt to identify a specific organism. This step is not only important for determining what antibiotic is appropriate, it can also help you find out whether the bacteria involved poses a risk to other horses, as might be the case for Streptococcus equi, the organism that causes strangles. 

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Step 3: What Is the Organism Sensitive to? When the lab performs a culture and identifies an organism, it’ll also run a sensitivity test to determine which antibiotics that specific organism will respond to. This will provide your veterinarian with a list of possible antibiotics that they can consider when determining the best option to treat your horse. 

Step 4: What Part of the Body Is Affected? Some antibiotics reach certain parts of the body better than others. For example, if your horse has a bone infection, your vet will choose an antibiotic that reaches high enough concentrations in the bone to be effective. And if your horse has an abscess, your vet will choose an antibiotic known to penetrate abscesses. 

Step 5: Are There Individual Horse Factors to Consider? Finally, your vet will take into account any individual factors about your horse that might limit the use of certain antibiotics. For example, if your horse has experienced any kind of kidney damage, some antibiotics should be avoided. And if your horse won’t tolerate injections, that may tip the decision toward an oral antibiotic if one is available. 

Responsible use of antibiotics isn’t as simple as it seems. But one thing is certain—it’s critical that we, as horse owners, start to pay attention to how the things we do might play a role in contributing to the emergence of antibiotic resistance. Simply eliminating “just in case” use of these important medications, and making sure we choose and administer antibiotics with care are the first steps we must take.