Facts About Heartworm Disease in Dogs and Cats

Heartworm disease has long been known as a problem that affects dogs, but it is a serious condition that can also occur in cats—even indoor cats, since no window screen is foolproof against mosquitos, which spread the disease. Animals can become infected with heartworms when bitten by a mosquito carrying parasitic worms called Dirofilaria immitis. The tiny worms enter the pet as microfilariae (larvae), but they eventually mature into adult heartworms that can cause serious complications in the pet’s heart, lungs, and blood vessels. 

Heartworm disease can be deadly, but it is preventable. Our team takes parasite control very seriously, and it is something we discuss with our pet families at every wellness care visit. 

To understand the dangers of heartworms in pets, read on. 

Heartworm Disease in Dogs

When a mosquito carrying microfilariae bites a dog, the tiny heartworm larvae enter the dog’s bloodstream through the bite wound. In about 6 to 7 months, the larvae mature into adult heartworms, with male heartworms reaching lengths of 4-6 inches and females growing to 10-12 inches. The adult heartworms are able to mate, and the females release offspring into the dog’s bloodstream—perpetuating the vicious cycle. Heartworms can live inside a dog for 5-7 years.

Signs of heartworm disease in dogs include:

• Mild cough
• Fatigue following mild to moderate exercise
• Persistent cough
• Wheezing/difficulty breathing
• A sickly appearance

Heartworm Disease in Cats

Cats are not typical heartworm hosts, as cats seem to have a natural resistance to heartworm infection. However, cats are still at risk—even indoor cats. And for cats with heartworm disease, the outlook is grim.  

Heartworms can live for only 2-3 years inside a cat, but because cats have smaller bodies and arteries than dogs, it takes just 1-3 worms to cause serious problems, including obstruction of blood flow and sudden death. 

Signs of heartworm disease in cats can range from mild to severe, including:

• Vomiting
• Trouble walking
• Lack of appetite/weight loss
• Wheezing/difficulty breathing
• Increased respiration
• Asthma-like coughing 
• Sudden collapse

Prevention is the Best Medicine for Heartworm Disease

The effects of heartworms on our pets can be devastating, but with proper care, heartworm infection is preventable. We strongly recommend year round, FDA-approved parasite control for cats (even indoor cats) and dogs to protect pets from the dangers of heartworm disease. 

Heartworm preventatives come in several forms:

• Topical liquids (for dogs and cats)
• Chewable and non-chewable medications (for dogs and cats)
• Injections (for dogs only)

Some parasite prevention products are also highly effective against intestinal worms (such as hookworms or roundworms, which are zoonotic), as well as pests like fleas, ticks, and ear mites.

At Conrad Weiser Animal Hospital, our team is committed to protecting your pets from heartworm disease. Please contact us if you have questions about heartworm prevention or to schedule your pet’s next visit.