Genetic Test For Herding Breeds Can Prevent Ivermectin Toxicity From Heartworm Meds

If you’ve ever been to a hospital emergency room, you already know the first question they ask you is if you are allergic to any drugs. While my response of “not sure, let’s try some” is rarely met with laughter, the truth is that this mini prompt can save your life if you are in fact allergic to some of the more common antibiotics on the market.

But what do you do if you’re a dog and no one is asking the question?

Related: Heartworm Treatment: What Are Your Options?

That’s what happened to a 4-year old Australian Shepherd named Bristol when he became deathly ill from a safe, commonly-used treatment to prevent heartworm. When he was rushed in to his local veterinary clinic last September, he was barely responsive and experiencing persistent seizures. His owner had googled his symptoms and suspected he was suffering from severe invermectin toxity.  Invermectin is the active ingredient in some of the heartworm prevention meds and when it crosses the blood-brain barrier it can cause neurological damage.

While the message here is not to arbitrarily stop meds that are proven to protect our pets from deadly heartworms, it does show the importance of acting swiftly when your pooch is seriously ailing.

Related: How Do Dogs Get Heartworm?

Bristol required immediate, aggressive medical intervention including a ventilator to keep her alive and an MRI brain scan to rule out other potential causes. She was then transferred to the Cummings School of Veterinary Medicine at Tufts University where it was a full 10 days before she was able to breathe on her own and three weeks before she regained consciousness. Recovery was slow and required her to re-learn how to walk using splints and a wheelchair.

It was a month before Bristol was back to her old self and able to walk, eat and drink on her.

So with millions of family pets being treated with heartworm meds each year, what the heck went wrong here?

Apparently, herding breeds like Bristol have a genetic mutation that makes them sensitive to invermectin and instances of toxicity can happen when dogs are exposed to higher dose versions of the drug.

How would they be exposed to higher than normal doses? It seems stronger doses of invermectin are used in livestock. While at a herding lesson, Bristol felt peckish and decided to sample from sheep feces from an animal that had recently been dewormed. Bingo-Bango, one sick little dog.

Although the products we use to prevent heartworm are typically safe and effective, many white-footed herding breed dogs like Bristol have a genetic mutation that makes them sensitive to it and several other drugs, including some common chemotherapy drugs. In those instances, alternative medications can be used.  Dr. Terri O’Toole, D.V.M., one of a team of critical care specialists overseeing Bristol’s care recommends that owners of herding breed dogs undergo a simple genetic test to determine if they have a mutation in the multidrug resistance (MDR1) gene.

“Getting the gene mutation test would enable them to know for sure if they could safely use some of these other drugs,” said O’Toole. “The kits are readily available through veterinarians, and they include a small brush that you use to take a swab of the inside of the dog’s mouth.” The swab is sent to a testing lab at Washington State University and the results could save your pooch’s life!

[Source: Science Daily]


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