How to Prevent Heartworm Disease in Dogs

Heartworm Disease Explained

Heartworm disease is a serious and potentially deadly disease that is caused by foot-long worms (heartworms) that cause severe lung disease, heart failure, and damage to other organs in the body. Although many animals can be affected, including cats, ferrets, wolves, coyotes, foxes, and even sea lions, dogs are most commonly impacted because they are a natural host. This means that worms can live inside the dog, mature into adults, mate, and produce offspring.

Contracting Heartworm Disease

Heartworm disease is caused by a parasitic worm called Dirofilaria immitis. It isn’t contagious, so a dog can’t catch the disease simply from being near an infected dog. However, it can be passed through just one bite from an infected mosquito.

After a mosquito bite, the heartworm life cycle begins. Tiny larvae (called microfilariae) begin to travel from the tissue to the bloodstream and eventually make their way to the chambers of the heart or lungs where they grow into adult heartworms.

Heartworms can grow anywhere between 4 and 12 inches in length, and when untreated, can cause lasting damage to a dog’s heart, lungs, arteries.

Heartworm Signs

During the early stages of heartworm disease, many dogs will show few signs or none at all, but as the infection persists and the disease progresses, more severe signs will likely develop. 

Subtle signs can include a slight cough, a decline in activity, and appetite or weight loss. Over time though, more severe signs may develop, including heart failure, muscle wasting, anemia, scar tissue in the lungs, and accumulation of fluid in the lungs and abdomen.

Heartworm Prevention

How can I prevent heartworm infection in my dog?

Since heartworm larvae are spread through mosquitoes, limiting mosquito exposure is a good start. You can reduce outdoor time for your dog during dawn and dusk when mosquitoes are most active. In addition, removing areas of standing water can help, as this is where mosquitoes breed. While environmental management is important, you’ll need to work with your vet to make a proactive medical prevention plan to really protect your dog.

What kind of heartworm preventative is right for my dog?

The American Heartworm Society recommends annual heartworm testing for dogs. If a test comes back negative, your veterinarian will walk you through different preventive options that are only available by prescription.

Preventives include monthly chewable pills, topical liquids, and an injectable medication that is given every 6 or 12 months. Many preventives work primarily for heartworms, but some can protect pets from a range of other intestinal parasites, including worms, fleas, ticks, and mites. Veterinarians will typically know which parasites are common in your area and can help you explore the best preventive for your dog.