LTDO Heartworm Feature with Dr. Elad Rosenfeld OVC Grad

Oct 23, 2023

After a long, particularly isolating winter, warmer days have been more than welcome. The thought of being outside more and enjoying some fresh air is downright critical for us, and our dogs. But the onset of Spring and Summer is also a reminder for pet owners to begin a really important annual process – heartworm prevention.

Temperatures matter when it comes to heartworm, a life-threatening condition transmitted by mosquitoes in which worms develop around the animal’s heart. Actually, the temperature that we need to be most aware of is 14 degrees Celsius. When both the days and nights are consistently at that mark or above, the heartworm threat for your dogs is real.

“That’s the temperature the larvae need in order to be infective,” says Dr. Elad Rosenfeld, a Guelph resident, and veterinarian at Preston Animal Clinic in Cambridge. “Between June and November, and maybe into December, mosquitoes can continue to transmit the disease.

“So between that time frame, we want to cover them with preventatives.

The effects of a dog (and in rare cases, cats) suffering from heartworm are horrendous. As larvae travel through the bloodstream to major vessels and large arteries, the worms can reproduce. This puts enormous stress on the heart, expanding the arteries and weakening the heart muscle. Symptoms would be similar to those of a human in congestive heart failure – coughing, shortness of breath, and exercise intolerance.

“The worms can cause clots and blockages, and potentially death,” says Dr. Rosenfeld. “The greater the burden of worms, the higher the risk. And once you have a large burden, it’s a different ballgame.”

Treatment at that point is both expensive and risky for the animal. The good news is that Dr. Rosenfeld doesn’t typically see a lot of dogs stricken by heartworm in that dangerous stage. And that’s because Canadians have been very diligent about the preventative measures needed to stamp out the disease. He says there is good herd immunity throughout the country’s pet population. And because it’s extremely difficult to stop your dog from getting a mosquito bite, that preventative course of medication, coupled with a blood test, is so important.

Dr. Rosenfeld encourages all owners to take their dog to their local vet to begin a personal parasite prevention program. It starts with an annual blood test, which also screens for Lyme’s disease, Anaplasmosis (a disease spread by ticks), and Ehrlichia (a bacteria also spread by ticks). Early detection leads to better treatment. And the vet can then establish what medication – taken in a monthly pill form throughout heartworm season – is best suited to your dog.

“There are some topical products on the market that claim to prevent mosquito bites but they aren’t 100 per cent effective,” says Dr. Rosenfeld. “Therefore, we choose to kill off the young larvae so that they can’t develop into the adult stage. Once the larvae are exposed to the medication, it kills them.

“Many people will say they don’t need the blood test because the prevalence is low and it’s never positive. But that test also screens for those other issues, like Lyme’s disease.”

A parasite prevention program is the smart thing to do for all dog owners. That way, you can enjoy those warm days knowing your furry loved one is safe.

“The more people who treat their dogs means the likelihood of heartworm in your area gets lower and lower,” Dr. Rosenfeld says.

Not So Fun Facts

  • Adult female heartworms can grow to a length of 10 to 12 inches, while male heartworms are 4 to 6 inches
  • Adult worms can live in a dog for up to 7 years
  • They produce microfilariae that circulate in the blood

For more information on heartworm, check out the following links: