Heartworm Disease

April is National Heartworm Awareness Month – probably because as April starts to get warmer and head into Summer, the mosquitoes who carry heartworm disease to our pets start to come out.

Heartworm disease is caused by a parasite called Dirofilaria immitis living in the pulmonary artery – the vessel between the left side of the heart and the lungs- in the dog and cat. This disease is spread by mosquito bites, leads to an 8-12 inch long worm living in the heart of your pet, and is life threatening. This disease has been diagnosed in dogs in all 50 states and is very common in our area.

What does heartworm disease do?

When a dog (or cat) is bitten by a mosquito carrying heartworm larvae, the mosquito drops the larvae on the pet’s skin, where it crawls into the bite wound and enters the blood stream. The larvae lives in the blood for approximately six months until it matures into an adult worm living in the vessels of the heart. In dogs, there are usually multiple worms involved in each infection (ranging up into the hundreds of worms), but in cats even one single worm can cause a significant amount of damage. In dogs, the adult heartworm lives for 5 to 7 years and produces microfilaria (another larval stage) that circulate in the dog’s blood to be picked up by a mosquito and start the cycle over. While the heartworm is living in the dog’s heart, it is making it difficult for blood to circulate and for the heart to do it’s job. The presence of heartworms can also lead to system wide inflammation and can go so far as to cause heart failure. In cats, a common symptom of heartworm disease is sudden death, with asthma-like symptoms and generally not feeling well being other commonly reported symptoms.


What can I do about heartworm disease?

The American Heartworm Society, as well as TotalBond, recommend regular heartworm prevention, year round, for all pets. Some people think they can stop giving heartworm prevention in winter months, but mosquitoes are tricky and can sometimes live indoors. For most  prevention products, you give your pet a monthly dose of medication either orally or topically. We do also have an injectable product for dogs that can be given by the veterinarian every six months. For dogs, we also recommend yearly testing for heartworm disease to make sure the parasite prevention program is working. These medications are highly effective, but skipped or late doses compromise their efficacy. Also, nothing in the world is 100% perfect and without testing, you won’t know if your pet needs treatment.


What happens if my pet is positive?

This is an important conversation to have with your pet’s doctor, as the exact treatment plan depends on a large variety of factors – especially your pet’s underlying health and the severity of their disease. In all dogs with heartworm disease, the first step is to restrict exercise. With a foreign material (the worm) living in the dog’s heart, any increase in heart rate makes the dog susceptible to pieces of the worm fracturing off and essentially causing a stroke. After your dog is stable, we can begin the process of actually killing the worms with an injectable medication. In cats, things are a little more difficult as we cannot directly treat the worms and have to manage the cat’s heartworm disease by controlling symptoms to make the cat more comfortable.


In conclusion, heartworms are a serious, sometimes fatal, condition in dogs and cats that can easily be prevented. In this case, an ounce of prevention beats a pound of cure.