The Modern Equine Vet
January 2024
Vol 14 Issue 1 2024
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Cover Story | Respiratory

How to Treat an Asthmatic That is Not Responding

By Marie Rosenthal MS

If you are dealing with an asthmatic horse that is not responding to treatment, the first thing to do is make sure it actually has asthma.

“Often with asthma, we make a relatively presumptive diagnosis, which is often correct. But there are rarer conditions out there, and sometimes, we have to go back and reevaluate where we are from a diagnostic perspective,” said Philip A.S. Ivens, MA VetMB, CEM(IntMed), DECEIM, MRCVS, EBVS, owner of Buckingham Equine Vets, in the United Kingdom.

Differential diagnoses include a viral or bacterial infection, a parasite, such as lungworm, which is rare, exercise-induced pulmonary hemorrhage, neoplasia or upper airway disease, Dr. Ivens pointed out at the 2023 BEVA Annual Congress, held in Birmingham.

“For these performance horses, exercise-induced pulmonary hemorrhages are definitely a possibility,” he said.

If the original diagnosis is confirmed as asthma, consider management: Did you just treat the symptoms or look at reducing inflammation? Did you attempt to control the environment?
These steps are at the core of asthma management, whether it is mild, moderate or severe, Dr. Ivens explained.

“We’re going to spend a reasonable amount of time looking at symptomatic versus anti-inflammatory treatment, I think still in practice and very reasonably, we tend toward more symptomatic treatment in terms of bronchodilators versus getting to the core of what this disease is, which is an inflammatory disease of the lower airway,” he said.

The key differentiation of mild, moderate and severe asthma—the current classification of the disease—is that severe asthma has tachypnea/dyspnea at rest, whereas the mild cases appear clinically normal apart from maybe a cough or nasal discharge, with underlying airway limitation and impaired gaseous exchange. Not all mild cases have cough, however, he said.

There are many environmental factors that inflame the airways of a horse with asthma, including molds and spores, their toxins, particularly in forage; plant debris and inorganic dust.

“These are the inflammatory agents in a stable environment,” he said. “The stable environment is naturally a very dusty place. And microbiologic products, endotoxin, peptidoglycan, bacterial DNA even, and mold and fungal products that produces toxins and beta glucans [are often present].

“Why is this important? We just need from a therapeutic perspective to keep a wider view on things—not all of what we’re dealing with is due to allergy,” he said.

2023 was a bad year in his Birmingham practice in terms of summer-pasture–associated asthma. “I’ve certainly had cases in the very extreme hot weather for the UK that had been very well controlled up until now, and a lot of these cases were next to busy yards,” he said.

“In human asthma, pollution is a big confounding factor with asthma exacerbation. I was wondering whether this was part of this sort of irritant effect on what is already underlying disease,” Dr. Ivens said.

Environmental control is the “bedrock of controlling all equine asthma cases,” Dr. Ivens said. “Environmental controls are often underestimated, and if you’ve got a non-responder, assuming that you are comfortable with your diagnosis, it’s the first place I would look.”

He called it imperative to visit the yard, walk around the environment and breathe the air yourself, and if possible, bring the client with you. He told the story of a Thoroughbred who had been winning quite a few races and was moved to a stable next to the trainer’s office, so it could be closely monitored. It started performing badly, and it turned out there were more air particles next to the trainer’s office, because there were more people going in and out and kicking up dust.

“Just that footfall was aerosolizing the dust in the environment, and therefore, causing performance issues in that horse,” he said.

After environmental controls, many veterinarians add bronchodilators, and then, as the clinical signs worsen, reach for corticosteroid treatment. As the disease gets under control, they then work down that pyramid eliminating medications.

“But I think the thing that has changed our understanding of equine asthma is that symptomatic relief with bronchodilators is probably, in most cases, not enough,” he said. The steroid can decrease the inflammation and improve the horse’s quality of life.

“I think as therapeutics evolve, more of these horses would benefit from more sustained and more prolonged corticosteroid treatment,” Dr. Ivens said.

However, corticosteroids are not without side effects, so it is important to practice the “yin and yang” of balancing steroids with the potential risk for laminitis. In athletic horses, this can be less of a problem because most of them are in better body condition. Pleasure horses today tend to be less conditioned and maybe a little overweight, which would already put them at risk for laminitis.

“I think it’s really important to diagnose your laminitis risk,” he said. Do a glucose challenge test to see the degree of hyperinsulinemia and check for any underlying endocrine disease, such as PPID, to make sure that steroids won’t aggravate any of these conditions.
And remember all steroids are not created equal, and the inhaled corticosteroids are intrinsically more potent than dexamethasone.

The challenge is getting that inhaled steroid to the site where we need the therapeutic effect. “So even though they are relatively more potent, it’s that delivery to the site of inflammation that is the challenge,” Dr. Ivens said.

Approved in 2020, the Boehringer Ingelheim Aservo EquiHaler, which delivers ciclesonide inhalation spray, in a soft mist, was the first FDA-approved inhalant therapy for horses with severe equine asthma. The inhaler includes an ergonomic handle and dosing lever that makes it easy to use, and a nostril adaptor that fits inside the nostril of the horse, allowing the horse to easily inhale the medicated mist into its lungs.

“In human medicine, there has been soft mist technology for quite some time. And we recently licensed an equine product that uses this,” he said. “With a soft mist that then can be inhaled, you lose much less drug in that upper airway.”
Nebulizers are also used, as are meter dose inhalers, but they fire the drug at a high velocity, and only about 20% of the medication is getting into the trachea and the lower airway.

Regardless of your delivery system, corticosteroids treat the inflammation, which is better than just providing symptomatic relief, Dr. Ivens said, which is especially important in non-responders.

“If a case is not responding, reevaluate the diagnosis and once you’re certain that this is an equine asthma case, treat the underlying inflammation; Don’t provide just symptomatic relief,” he recommended. “Improve the environment where possible while you’re getting the disease under control, because in the long term to de-escalate your therapeutic intervention, that’s going to be key.

“Finally, think how best to deliver the corticosteroids and which corticosteroid to use depending on the individual patient’s circumstances.” MeV

 

Using the Aservo EquiHaler to treat a horse with asthma.
Image courtesy of Boehringer Ingelheim