What Is Heartworm Disease in Dogs?

Heartworm disease in dogs is a serious and potentially life-threatening condition that is caused by a parasitic worm called Dirofilaria immitis. These worms are transmitted through the bite of an infected mosquito, and once inside your dog’s body, they travel through the bloodstream, eventually settling in the heart, lungs, and surrounding blood vessels. Over time, these worms can grow up to a foot long and multiply, causing significant damage to your dog’s organs and overall health.

While it might sound like something rare, heartworm disease is unfortunately common in many parts of the United States, especially in warm, humid regions where mosquitoes thrive. But even dogs in cooler or drier climates aren’t immune as it only takes one mosquito bite to start an infection.

How Dogs Get Heartworm Disease

Heartworm disease in dogs starts with a mosquito bite. When a mosquito carrying heartworm larvae (called microfilariae) bites a dog, those microscopic larvae enter the dog’s bloodstream. Over the next several months, the larvae mature and migrate to the heart and pulmonary arteries, where they continue to grow into adult worms.

Once mature, these worms reproduce and release more microfilariae into the bloodstream, allowing the cycle to continue when another mosquito bites the infected dog. Without treatment or prevention, these worms can live for five to seven years inside a dog’s body, causing serious and often irreversible damage.

The disease is rare in puppies because the microfilariae take five to seven months to mature into adult heartworms after infection.

Signs and Symptoms of Heartworm Disease

The tricky part about heartworm disease in dogs is that symptoms often don’t appear until the infection has already progressed. In the early stages, dogs may seem completely normal. As the disease advances, you might notice subtle changes in your dog’s behavior and energy levels.

 A mild, persistent cough is one of the first signs that something might be wrong. Over time, your dog may begin to tire easily after moderate activity or show reluctance to exercise at all. As the infection worsens, symptoms such as difficulty breathing, fatigue, loss of appetite, and weight loss become more apparent. In severe cases, dogs may develop heart failure or fluid buildup in the abdomen, known as ascites.

 Unfortunately, by the time these symptoms appear, significant heart and lung damage might already have occurred. That’s why early detection and prevention are so important when it comes to heartworm disease in dogs.

 Diagnosing Heartworm Disease

If your veterinarian suspects heartworm disease, they’ll start with a simple blood test designed to detect heartworm antigens or microfilariae in your dog’s bloodstream. This test is quick and accurate, and it’s often part of a dog’s annual wellness exam, especially in areas where mosquitoes are prevalent year-round.

If the initial test comes back positive, your vet may recommend additional diagnostic tests such as X-rays, ultrasounds, or more specific bloodwork to determine the severity of the infection and how much damage the worms have caused to the heart and lungs. These results will help guide the safest and most effective treatment plan for your dog.

Treatment for Heartworm Disease in Dogs

Treating heartworm disease in dogs is possible, but it’s not a simple process. Because the worms live in such sensitive areas of the dog’s body, the heart and the lungs, the treatment must be done carefully to avoid complications. Typically, treatment involves a series of injections that kill the adult worms, along with medications to eliminate the immature larvae and reduce inflammation.

During this time, it’s imperative to restrict your dog’s activity. When adult worms die, they can break apart and travel through the bloodstream, potentially causing dangerous blockages. Keeping your dog calm and limiting exercise allows your dog’s body to safely clear the dead worms.

Depending on the severity of the infection, recovery can take several months. In advanced cases, hospitalization or supportive therapies may be needed to help your dog’s body recover.

Preventing Heartworm Disease

The good news is that heartworm disease in dogs is almost entirely preventable. A variety of safe and effective heartworm preventatives are available through veterinarians, including monthly oral tablets, topical medications, and injectable options that provide protection for several months at a time.

These preventatives work by killing any immature heartworm larvae before they have a chance to mature into adult worms. Consistency is key: missing even one dose can leave your dog vulnerable to infection. Your veterinarian can recommend the best prevention plan based on your dog’s lifestyle, age, and health status.

It’s also important to remember that heartworm preventatives should be given year-round, not just during mosquito season. Mosquitoes can survive indoors or appear during warm spells, even in colder climates.

Why Prevention Is Always Better

While heartworm treatment can be effective, it’s expensive, time-consuming, and physically hard on your dog. Prevention, on the other hand, is safe, affordable, and simple. Protecting your dog from heartworm disease isn’t just about avoiding the infection, as it’s about preserving their long-term heart and lung health, and ensuring they live a full, active life.

Even if your dog spends most of their time indoors, it’s still important to stay consistent with prevention and annual testing. Mosquitoes only need a small window of opportunity, and the risks far outweigh the minor cost of a monthly preventative.

Final Thoughts

Heartworm disease in dogs is a serious but preventable condition caused by a parasitic worm spread through mosquito bites. Left untreated, it can lead to severe heart and lung damage, and even death. But with regular testing, year-round prevention, and early intervention, you can protect your dog from this dangerous disease and keep your pups’ tail wagging for years to come.