Symptoms of Heartworms Explained: How Do Dogs & Cats Get Heartworms?

Heartworm disease is a serious and potentially fatal condition that affects dogs, cats, and other mammals. But how do pets get heartworms, and why is this parasite so dangerous? Many pet owners don’t realize that heartworms live inside an infected pet’s heart and lungs, specifically in the pulmonary arteries, making them nearly invisible until the disease has progressed. At Safe Harbor Animal Hospital, we want to ensure every pet owner understands the risks and the importance of prevention.

Symptoms of Heartworms Explained: What Is a Heartworm?

Heartworms (Dirofilaria immitis) are parasitic worms that as adults, live in the heart, lungs, and blood vessels of infected animals. Immature heartworms are known as the “larval stage.” Larvae primarily live in the blood stream of your pet and are visible only with a microscope. The adult worms can grow up to 12 inches long and multiply inside the body, leading to life-threatening complications. Because they reside deep within the body, heartworms are not visible to the naked eye, making early detection difficult.

Symptoms of Heartworms Explained: Understanding the Transmission Process

Heartworms are transmitted through mosquito bites. When a mosquito bites an infected animal, it ingests microscopic heartworm larvae called microfilaria. These larvae develop further inside the mosquito and are then transmitted to a dog or cat in the form of a later larval stage (L3) when the mosquito feeds again. Once inside a pet’s body, the larva migrates through the bloodstream, eventually settling into the heart and lungs. Over time, they grow into adult worms that can cause severe organ damage.

Symptoms of Heartworms Explained: Guess What? It’s Not Just Dogs!

While heartworm disease is most common in dogs, other animals, including cats and ferrets, also be affected. Cats experience heartworm differently. Signs of heartworms in cats can vary from subtle signs, like coughing, to severe signs, like collapsing and acute death. Unfortunately, there is no approved heartworm treatment for cats, making prevention even more critical.

Symptoms of Heartworms Explained: Why Don’t We See Heartworms? Understanding the Silent Killer

Heartworms live inside an infected animal’s internal organs, meaning they are not visible on the skin, fur, or in the poop. This makes early detection difficult, as many dogs show no signs of infection until the disease has progressed. Clinical signs of heartworm disease include:

  • Persistent Coughing – As worms accumulate in the lungs, they cause breathing difficulties. Especially with exercise.
  • Lethargy & Weakness – Dogs with heartworm disease often tire easily and become less active.
  • Weight Loss & Decreased Appetite – Severe cases can lead to muscle loss and weakness.
  • Swollen Abdomen – Advanced heartworm infections can cause right-sided heart failure leading to fluid buildup in the abdomen.
  • Collapse & Sudden Death – In severe cases, untreated heartworm disease can be fatal.

Because symptoms don’t appear until later stages, annual heartworm testing and year-round preventive medication are essential.

Symptoms of Heartworms Explained: The High Cost of Treatment vs. Affordable Prevention

Heartworm treatment is available for dogs but not for cats. However, heartworm treatment for dogs is not only costly; it’s risky. The treatment process involves multiple injections of an arsenic-based medication (melarsomine), strict exercise restrictions, and months of recovery time. In contrast, monthly heartworm prevention is affordable, easy to administer, and highly effective in protecting your pet.

To learn more about parasite prevention for dogs, watch this video!

Symptoms of Heartworms Explained: Protect Your Pet with Year-Round Heartworm Prevention

Heartworm disease is a deadly but preventable condition with a simple annual test that requires just 3 drops of blood. At Safe Harbor Animal Hospital, we recommend annual heartworm testing and year-round prevention to keep your pet safe. If your dog isn’t on heartworm prevention or you have questions about the best heartworm medication, contact us today at (843) 648-4787 or book an appointment online.

Safe Harbor Animal Hospital in Mount Pleasant, SC, is part of a locally owned, family-owned network of animal hospitals known as Animal Hospitals of the Lowcountry. Our network includes:

  • Mount Pleasant Animal Hospital: South Mount Pleasant SC, At Coleman Blvd and Old Village
  • Shuler Veterinary Clinic: Central Mount Pleasant SC, At Town Center
  • Safe Harbor Animal Hospital: North Mount Pleasant SC, At North MP and Hwy 41

Let’s work together to keep our pets, families, and community safe!