Bristol and owner Laura Liebenow of Greenfield, Mass., snuggle on the day of Bristol’s discharge.

Ivermectin is the active ingredient in some heartworm prevention medicine. Despite its general safety, it can be toxic for some herding dog breeds. But it’s easy enough to find out, thanks to a simple genetic test. Luckily for one dog, that test saved her life.

In September, the Cummings School of Veterinary Medicine and its Foster Hospital for Small Animals treated Bristol, a four-year-old Australian shepherd, who was experiencing persistent seizures.

After other causes were ruled out, hospital staff tested Bristol to see if she had a genetic mutation in the multidrug resistance (MDR1) gene that made her sensitive to ivermectin and some other common chemotherapy drugs.

The researchers hit gold, and by mid-October Bristol was back to normal.

The case was published in Phys.Org on Oct. 20.

 “There are not many cases with happy endings like this,” said Meghan E. Vaught, DVM, who treated Bristol during her 40-day hospital stay. “This is a huge success story.”

Although products containing ivermectin are typically safe and effective, many white-footed herding breed dogs have a genetic mutation that makes them sensitive to it and several other drugs, including some common chemotherapy drugs.

The ingredient can also be ingested indirectly. (Bristol had ingested the feces of sheep that had recently been dewormed with a product containing ivermectin.)

O’Toole recommends that owners have their herding breed dogs undergo a simple genetic test to determine if they have a mutation in the multidrug resistance (MDR1) gene.

“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.

Photo Credit: Andy Cunningham, Tufts University, © Copyright 2015 Tufts University

Comments (2) -

C Beadnell
C BeadnellUnited States
11/13/2015 11:29:35 AM #

I was always told Ivermectin should not be given to any Collie breed of dog. Just an FYI

B Wallace
B WallaceUnited States
11/16/2015 3:35:50 PM #

This was before the genetic testing was available. It was known that some breeds, especially collies, have a sensitivity to Ivermectin. So to be safe, collies were not given ivermectin. Now they have isolated the cause as a mutant gene that some dogs have. Anywhere from 70-90% of collies have the mutant MDR1 gene. Over a dozen other breeds are also known to have this, with more being added. It is an easy test that the owner can submit through their Veterinarian or directly with Washington State University. A cheek swab or blood is accepted. Ivermectin is not the only drug that is dangerous to them. There is a known list of drugs to avoid, with more being added as they are confirmed.

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