What are Heartworms?

Classified as Dirofilaria immitis, this parasitic roundworm is more commonly known as heartworm, or dog heartworm.  Spread from host to host through the bites of mosquitoes, these small, thread-like worms infect the bloodstream of the host, leading to Heartworm Disease.

What is Heartworm Disease?

Once successfully infecting a host, heartworms take up residence in pulmonary arteries and the right side of the heart, attaching to the interior muscle and living off the host’s tissue and blood.  The parasites chew on the heart muscle with sharp teeth, and impede normal blood flow through the heart valves with their bodies as they grow in size up to 12 inches in length.  Living as long as 5 to 7 years, adult heartworms begin to shed debris into the host’s lungs, including excrement, offspring, and segments of their bodies.  Heartworm disease in dogs first develops as a cough from the severe inflammation in the lungs, later progressing into heart failure as the parasites grow in size and number, at times well into the hundreds.

How is it Treated?

To stop the progression of the disease, the heartworms must be killed with an arsenic derivative.  The treatment is expensive, time consuming, and carries a risk proportional to the burden of worms present in the heart.

How is it Prevented?

Prevention is easy, inexpensive, and very effective.  For dogs, the chance of becoming infected by heartworms if bitten by a mosquito carrying the larva is around 90%, and there is always a risk of exposure regardless of how briefly the animal spends time outside.  We recommend year round protection as the seasonal activity of mosquitoes can be unpredictable with early thaws and longer periods of warmer weather.  We currently carry Heartguard Plus, Sentinel, Sentinel Spectrum, and Revolution, and we can help you decide which product is best suited to your pet’s needs.  These preventatives have the added benefit of treating and preventing other parasites such as roundworms.  We also annually test for the presence of microfilaria, the early small larval stage of heartworms.  Unlike other parasite tests in which we require a fecal sample, this test is run using a small blood sample.

Cats can also become infected with heartworm.  The good news is that cats are naturally resistant to heartworm, and may not develop an infection if bitten by an infective mosquito.  The bad news for cats is that due to their smaller size, a single heartworm in a cat is enough to cause serious illness and death, and there are no current treatment options for cats with heartworm disease, though preventatives are also available in the form of Heartgard for Cats, Interceptor for Cats, and Revolution.  These feline heartworm preventatives also have the added benefit of treating and preventing other parasites, including roundworm.  Unlike dogs, cats do not require a blood test prior to starting a heartworm preventative.

The Life Cycle of Heartworm

For more in depth information, please visit the nonprofit  The American Heartworm Society .
For product comparison and other information please visit the Heartworm Information Center .