Heartworm disease can be fatal, but fortunately, it’s easy to prevent this disease from needlessly occurring in so many pets. Because it is so easily preventable, it can be very frustrating for veterinary practitioners when we see these cases.

Treatment involves a month of strong antibiotics, followed by an injectable arsenic derivative compound that can be very hard on the animal. While heartworm treatment protocol and medications have come a long way over the decades in terms of safety and efficacy, there are still risks to treatment in sensitive pets.

In addition to soreness at the site of the injection treatments, many animals may become restless and/or develop fevers. In animals heavily infected with heartworms, chronic irreversible changes in the right side of the heart may be present, in addition to pathology of the lung arteries, as well as other organs in the body including the liver and kidneys. Many animals will present with severe and chronic coughing, as well as fluid retention in the chest and abdominal cavities.

Not only may animals have acute reactions to the heartworm treatments over a few months, but it is critical that guardians rest their pet during heartworm treatment protocols, or they may succumb to potentially fatal blood clots.

From this extensive list of potential complications, it certainly makes better sense to prevent this potentially fatal disease., rather than go through the above treatment that may be harsh on many animals.

Heartworms are carried by infected mosquitoes that transmit parasitic worms that grow in the arteries of the lungs and hearts of dogs, cats and many other mammals. The heartworm larvae enter the mosquito bite wound and move through the animal’s body. Heartworms can grow up to 12 inches long in some cases.

Fortunately, the disease is not transmissible between pets, but given the potential above complications to heartworm infection, this is not a disease that one should ever want their animals to suffer through.

The FDA has approved several heartworm preventative medications for dogs and cats, which are available in the form of oral tablets, injectable medications and topical treatments. However, all heartworm preventatives target the immature heartworm larvae, but not the adult heartworms, which are responsible for most of the pathology in the heart and lungs. This is a major reason why veterinarians recommend year-round heartworm prevention.

Although there are fewer number of mosquitoes present in the winter, winters have been warmer in recent years, where mosquito development has been documented, and thus there is still a risk that an animal could contract heartworms if the animal guardian stops giving medication during the winter months.

One never knows when the last mosquito is going to die and when the first mosquito is going to come out. Heartworms have been documented in dogs in all 50 states, so animal guardians who live in colder states may still have pets who are at risk.

Animal guardians who stop giving preventative during these cooler months run the risk of their animal contracting heartworms. If an animal becomes infected, and clients later resume giving the heartworm preventative, there may be a danger to certain animals who may be positively infected.

The preventative medication can kill so many microfilariae (baby heartworms) at once, that it could shock the animal’s system, and/or lead to blood clots which could be fatal. That is why veterinarians are so strict about recommending annual heartworm testing, so as to avoid these potentially dangerous complications of giving preventative to this subpopulation of already infected animals.

Dogs that have heartworms may not show symptoms in the early stages of infection, while veterinarians can easily test the dog with a simple blood test. Annual testing is always recommended because while the drugs are excellent in preventing heartworm disease, no drug is 100% effective.

And for those clients who have pets who rarely or never go outside, mosquitoes can easily access the indoor environment through windows and open doors, and thus pose a risk for heartworm transmission to even these indoor pets.

Unlike for heartworm disease in dogs, there is no FDA approved treatment of killing adult heartworms in cats. Because of additional complications associated with diagnosing and treating cats, year-round prevention is the best weapon against heartworm in cats.

The take home point of this article is to make sure your dog or cat is on year-round heartworm preventative, as well as to make sure your animal companion gets at least an annual exam and evaluation, as well as yearly heartworm blood test.

Dr. Michael Dym, VMD