At any given moment in time it would be most difficult to estimate how many herding dogs are roaming the fields, pastures and barnyards of this country. To watch them work puts many of us to shame as they respond to the hand signals and whistles of their Shepherds with a zeal that never ceases to amaze. Unfortunately some of these animals have inherited a defective gene that puts them at risk for a potentially deadly illness.
It has been found that white-footed herding dogs may have a genetic mutation that can trigger a serious reaction when they ingest the commonly used worming product ivermectin. Using a simple oral swab, dogs carrying this mutant gene can be identified. Your local veterinarian should have or be able to obtain these test kits. The swabs are submitted to the lab at Washington State University, School of Veterinary Medicine for analysis. By identifying susceptible dogs, owners and breeders can take the steps necessary to eliminate suspect animals from the breeding stock and avoid contact with products containing ivermectin. Other commonly used drugs affected by the MDRI gene mutation include acepromazine, butorphanol, erythromycin, loperamide, milbemycin and vincristine. This list is not complete so when in doubt check it out.
Current estimates suggest that half of Australian Shepherds may carry this defective gene and almost three out of four in the Collie breed. Owners of these breeds would do well to have their dogs checked if they are in locations where livestock may have been treated with ivermectin and the dogs have access to their feces.
Ivermectin has been used as a wormer for over 30 years and has stood the test of time proving to be both effective and safe in the vast majority of cases. It is derived from soil microorganisms and belongs in a class of drugs called macrocyclic lactones that includes avermictans and mibemycins. When it first came on the market it was used intramuscularly in horses and this caused some problems early on but as products were developed using other routes of administration these issues resolved. Its use in lactating dairy cows is prohibited but is permitted in most other livestock with withholding times established for those destined for slaughter.
The mutation that is responsible for the illness in some herding dogs is found on gene MDR1 and involves a substance called glycoprotein that in its normal state regulates the flow of drugs to the brain. In its mutated state it can no longer carry out its normal function allowing for the passage of drugs into the brain that, under normal circumstances, would be eliminated by other routes such as the kidneys. When drugs such as ivermectin are shunted into the brain, a rapid downhill course is set in motion that requires immediate medical intervention.
Such was the case with Bristol, a female Australian Shepherd, who was admitted to the Foster Hospital for Small Animals at the Cummings School of Veterinary Medicine, North Grafton, MA in early September. Bristol’s owner Laura Liebenow of Greenfield, MA is a dog trainer who was aware of her dog’s predisposition for an acute episode if she ingested ivermectin or other drugs that react in a similar way. Bristol’s episode started when she was at a herding lesson and ingested sheep feces from a flock that had been recently treated with ivermectin.
On admission to the Foster Hospital her condition was quickly evaluated and emergency support treatment begun. The owner had a high level of suspicion regarding the probable cause of Bristol’s problem and shared her concerns with the clinical staff. On admission Bristol was barely responsive and experiencing persistent seizures. A mechanical ventilator was employed and a brain MRI was performed to rule out other possible contributing factors. Dr. Terri O’Toole, one of the critical care specialists assigned to the case, remarked that it took a great deal of intervention without which this condition would have been fatal. Within 10 days Bristol began to breathe on her own although she remained unconscious for three weeks after admission. In due time she began walking with support from a cart and leg splints moving on to walking under her own power with assistance from the hospital staff. One month into her hospital stay Bristol began to behave as her normal self-regaining the ability to eat, drink and walk.
Dr. Megan Vaught another of Bristol’s attending clinicians said,” there aren’t many cases as difficult as this that end up with happy endings; this was a huge success story.
To those readers who enjoy the company and antics of an Australian Shepherd take all necessary measures to insure that your charges are protected from all of the hazards lurking out there in the countryside.