Heartworm disease is a serious parasitic infection caused by worms invading the greater blood vessels of the heart and lungs. Heartworms are transmitted by mosquitoes, which acquire the worms by feeding from infected wildlife or domestic animals. When a mosquito ingests blood from an infected animal, the mosquito also consumes tiny worms (called microfilaria). These microfilariae develop inside the mosquito and are then deposited into their next victim. These microscopic organisms slowly make their journey to the blood vessels in the pet’s heart and lungs, maturing and growing in size along the way. Once inside the heart and lungs, these worms continue to grow and multiply.Heartworm

Frighteningly, there are no signs when our pets initially contract heartworm disease. Signs are only seen once the worms have begun to overtake space in the blood vessels of the heart and lungs. Even as the disease progresses, diagnosis is tricky because signs of the illness are vague, like coughing, lethargy, shortness of breath, or overall malaise. Unfortunately, once heartworm disease starts causing signs, the worms have damaged the heart (likely permanently), often leading to death. The disease process generally takes two to four years to manifest, which is why annual testing is so important. When caught early, we have a much better chance of treating the disease.

dog and mosquitoSadly, heartworm disease is an increasing problem in Canada, with hundreds of cases being reported each year. The vast majority (70-80%) of cases are discovered in Southern Ontario – our backyards!Why the increased prevalence? Experts blame a variety of reasons, one being a surge of rescue animals being brought over from warm climates carrying heartworm disease. With an increased heartworm-positive population, mosquitoes have more opportunity to feed from infected animals, thus widely transmitting the disease. Compounding this problem is a decrease in the use of preventive medications. With an interest in more natural therapies, some pet owners are opting out of using heartworm medications. Unfortunately, no natural therapy has any scientific evidence to eliminate or prevent heartworm disease. The fact remains, without preventive treatments, virtually all dogs that are exposed to microfilaria will become infected. Veterinary heartworm preventive medications are extremely safe and are 100% effective at preventing heartworm disease. “Indoor” pets are also at risk of developing heartworm disease. Mosquitoes prefer warm temperatures and look to migrate indoors as the temperatures drop in the evenings. Indoor pets are not precluded from developing the disease and should also be on preventive treatments. Another possible reason for increased heartworm disease rates is our overall warmer temperatures. Without a harsh, cold winter, mosquitoes are able to survive, which prolongs the period during which heartworm disease is active in Ontario. Finally, with natural evolution and adaptation, mosquitoes are also evolving to survive in cooler temperatures, again, extending the period of heartworm activity.

Amazingly, heartworm is COMPLETELY PREVENTABLE! Monthly treatments should be given to our pets during mosquito-active months (June to November) to ensure our pets don’t develop this horrible disease. Many of these treatments have the added benefit of preventing a host of other conditions. Please contact our clinic to book your furry family’s annual heartworm testing and learn more about prevention options!