Heartworms are a serious and potentially fatal disease that mainly affects dogs, cats and ferrets. It is caused by the parasitic worm Dirofilaria immitis, which infects pets through the bite of an infected mosquito.
In dogs, once the heartworms mature, they travel to the heart, lungs and arteries, then mate and produce offspring, increasing the number of worms that the dog carries over time. These worms cause damage and scarring to these vital structures which can affect their overall health and the quality of life of the animal the longer they go untreated. If left untreated, the complications can eventually lead to heart failure, permanent lung damage and death.
BEFORE you start your pet on a heartworm preventative, your veterinarian generally will test your pet by drawing blood, to make sure your pet does not have heartworms before starting them on a preventative.
Equally important to the pre-test for heartworms is identifying the Multidrug Sensitivity gene in breeds affected by this mutation.
What is the Multi-drug Resistance Gene?
The MDR1 gene, or multi-drug resistance gene, codes for a protein that is responsible for protecting the brain by transporting potentially harmful chemicals away from the brain. In certain breeds, a mutation occurs in the MDR1 gene that causes sensitivity to Ivermectin, Loperamide, and a number of other drugs. Dogs with this mutation have a defect in the P-glycoprotein that is normally responsible for transporting certain drugs out of the brain. The defective protein inhibits the dog’s ability to remove certain drugs from the brain, leading to a buildup of these toxins. As a result of accumulation of toxins, the dog can show neurological symptoms, such as seizures, ataxia, or even death. Dogs that are homozygous for the MDR1 gene, meaning that they have two copies of the mutation, will display a sensitivity to Ivermectin, and other similar drugs. Dogs that are heterozygous, meaning they have only one copy of the mutation, can still react to these drugs at higher doses. The following is a partial list of drugs known to have a negative effect on dogs with the MDR1 mutation: Acepromzazine, Aldosterone, Amitriptyline, Antiemetics, Apomorphine, Buprenorphine, Butorphanol, Chinidin, Cimeditine, Cortisol, Cysolporin A, Dexamethasone, Digoxin, Diltiazem, Domperidone, Doxorubicin, Doxycycline, Ebastine, Erythromycin, Estradiol, Etoposide, Fentanyl, Fexofenadine, Grepafloxacin, Hydrocortisone, Ivermectin, Itraconazole, Ketoconazole, Loperamide, Losartan, Methylprednisolone, Metoclopramide, Metronidazole, Milbemycin, Mitoxantrone, Morhpine, Moxidectin, Ondansetron, Paclitaxel, Phenothiazines, Phenytoin, Quinidine, Ranitidine, Rifampin, Rifamycin, Selamectin, Sparfloxacin, Tacrolimus, Tetracycline, Verapamil, Vinblastine, Vincristine. Additional drugs beyond this list could have a negative effect on dogs with the MDR1 mutation and it is recommended to consult a licensed veterinarian for more information.
Breeds Affected by MDR1
- Australian Shepherd
- Border Collie
- Collie
- English Shepherd
- German Shepherd Dog
- Long-haired Whippet
- McNab
- Old English Sheepdog
- Shetland Sheepdog
- Silken Windhound
Link to the MDR1 Test
You can locate the GenSol MDR1 test by following this link: Multidrug Sensitivity (MDR1)
Other Helpful Links
Photo credit Summer Johnson
