When you bring your dog or cat to Pets & Friends Animal Hospital for heartworm testing and a prevention plan, we will now make you aware of heartworm resistance. Some pets are acquiring heartworm disease despite a prevention regimen. 

Colorado, which historically has had a low heartworm disease rate, has seen a rise in cases over the past 11 years. Researchers believe that a spike in cases from 2013 to 2017 was the result of an influx of more than 114,000 dogs that were sent to the state by more than 130 animal shelters and rescue groups hoping to find them forever homes. Some of these dogs had heartworm disease, and some of the infective heartworms had developed a resistance to the macrocyclic lactones, which are the major active ingredients of the commonly used heartworm preventives (i.e., ivermectin, selamectin, milbemycin oxime, and moxidectin). 

What is heartworm disease in pets?

Pets become infected with heartworm disease through a bite from an infected mosquito that transfers microscopic larvae (i.e., microfilariae) to the pet. The microfilariae travel through the pet’s bloodstream for about six months to the pet’s heart and large vessels, mature into foot-long worms up to 12 inches in length, reproduce, and cause respiratory and cardiac issues that can be life-threatening. As many as 30 to 100 worms can live in one dog’s heart.

Cats carry only a few worms in their smaller heart, but the worms affect cats differently and can cause significant inflammation known as heartworm-associated respiratory disease (HARD). Often, sudden death is the first disease sign in cats.

Heartworm disease treatment in pets: Prevention is key

Heartworm treatment in dogs is lengthy, painful, and costly, and involves deep lumbar injections that frequently cause swelling, pain, and loss of appetite. Dogs must also be severely exercise-restricted for at least four weeks, because pieces of dead heartworms can form dangerous clots. No treatment is currently available for cats. 

Obviously, a prevention protocol and full compliance, which can be easy to follow, as well as less expensive, is key for your dog and cat.

Lack of awareness and compliance are problems for pets

Lack of recognition about the seriousness of heartworm disease is still a problem, but one that, fortunately, pet owners can easily help resolve with awareness. A recent survey of 1,000 dog and cat owners revealed that:

  • Nearly 40% don’t believe their pet is at risk for heartworm disease.
  • 21% don’t believe that mosquitoes in their state carry heartworms.
  • 51% skip year-round prevention.
  • 41% don’t believe that their pet is always at risk.
  • 18% provide protection for their pet only in spring and summer.

Heartworm prevention in pets

Your veterinarian can help you develop an individualized prevention plan for your pet. At your pet’s annual wellness screening, they will test for heartworms, discuss the various preventive formulations, and help you choose the best product for you and your pet. Formulations include:

  • Injectables — These can be administered by your veterinarian every 12 months for dogs and six months for cats. With injectables, you don’t need to remember monthly treatments.
  • Topical liquids —These must be applied monthly to your pet on a spot they cannot reach (e.g., behind their head).
  • Chewables — Many pets prefer these flavorful pills, which must be given monthly.

Remember, prevention plans are only effective with year-round compliance and ensuring you never miss a dose.

Another problem: Resistant heartworms are now “real” for pets

“I believe that heartworm disease is the most important disease of dogs in this country, and I believe that the concern about resistance is the biggest problem that we face,” Clarke Atkins, DVM, DACVIM, said in an article published recently by the American Animal Hospital Association (AAHA). Veterinary cardiologist Dr. Atkins is professor emeritus of medicine and cardiology at North Carolina State University College of Veterinary Medicine, an American Heartworm Society executive board member, and an expert on the phenomenon of resistance. 

The resistance is real, Atkins said, although the extent of the problem is not yet known. The resistant heartworms come not only from the Mississippi Delta, and not necessarily from areas where resistance has been a concern. Resistance has also been found to be hereditary.

Heartworm disease and resistance will continue to be problems for pets in the United States and Colorado. Pharmaceutical companies and researchers will continue to study methods to conquer resistance, but in the meantime, year-round prevention is critical for your dog or cat. 

So, pet owners, ensure your beloved pet is fully protected. This applies to all pets, from pampered kitties who never set a paw outdoors, to canine entertainers who are the life of the dog park party. Contact our veterinary team at Pets & Friends Animal Hospital today and make an appointment for your pet’s heartworm test and prevention plan.