Heartworm Disease in Cats

What is heartworm disease?

This bloodborne parasite (dirofilaria immitis) lives in the heart or nearby large blood vessels of infected animals. Female worms are about 6 to 14 inches along (15 to 36 cm) and ⅛ in. wide (3 mm). Males are approximately half the size of the female.

Though heartworm disease is more commonly found in dogs than cats, it is possible for cats to become infected. Usually, cats have fewer adult worms than dogs (typically less than six).

What are symptoms of heartworm disease in cats?

While heartworm disease is often undiagnosed in cats, even immature worms can do extensive damage by causing heartworm associated respiratory disease (HARD) and issues in the immune system.

Heartworms can even move to other parts of the body, such as the spinal cord, eye or brain. Severe complications including blood clots in the lungs and lung inflammation can happen when adult worms die in the cat’s body.

Symptoms of heartworm disease may be subtle or apparent, and there are few, if any, early signs. Symptoms such as these may appear:

• Asthma-like attacks
• Difficulty walking
• Fluid accumulation in abdomen
• Fainting or seizures
• Coughing
• Periodic vomiting
• Lack of appetite
• Weight loss

Tragically, in some cases the first sign of heartworms in cats is collapse, or sudden death. And while medication used to treat heartworm in dogs may be effective, it cannot be used in cats. Therefore, this condition can be managed in cats but there is no clinical treatment. For cats, the best protection is prevention.

What causes heartworm disease?

A mosquito feeds on an infected cat, then picks up immature heartworm larvae which develop for 1o to 30 days inside the mosquito’s gut before entering its mouth parts. The infected mosquito then bites the cat and injects its infected larvae.

These larvae move through the bloodstream to the pulmonary arteries and the heart’s right side, where they grow into adult heartworms able to reproduce in about 6 to 7 months. At approximately 8 months after the cat has been infected, a new crop of larvae are born and reside in the cat’s blood for approximately one month.

While dogs have been known to have several hundred heartworms in their bodies, few of these larvae are usually found circulating in this area by the time testing occurs. Most do not survive to the adult age, as the cat is not a natural host.

Heartworms are transmitted through mosquitoes - not from one cat to another or from an infected dog to a cat directly. The risk of infection is highest when mosquitoes are present in the environment and actively feeding, and indoor cats are not immune; an infected mosquito may easily get into the house and infect a cat.

How is heartworm disease in cats treated?

Because heartworm disease is serious and progressive, the earlier your cat is tested and diagnosed, the better. Your veterinarian will take a small sample of blood from your cat, which will then be tested for heartworm proteins.

At LakeCross Veterinary Hospital, we process heartworm tests in our in-house laboratory, which allows us to get same-day results. If a cat tests positive, further tests may be ordered, and x-rays or ultrasounds may be required. While there is no drug approved to treat heartworms, the goal is to stabilize your cat and chart a long-term plan to manage the disease.

Treating heartworm infections in cats is risky. Though the heartworms may clear up, the damage caused may be permanent. If worms have been detected in the lungs, your vet may recommend chest x-rays every t to 12 months.

If mild symptoms are noted, small doses of prednisolone may be necessary to reduce inflammation. Severe heartworm disease could mean hospitalization so your cat can receive intravenous fluids, antibiotics, drugs to treat organ issues, and surgery in some cases.

How can I prevent heartworm disease?

We strongly recommend that all cats receive year-round heartworm preventives to be taken orally on a monthly basis in areas where mosquitoes are active, starting at eight weeks of age. Where mosquitoes are seasonal, preventive measures should be taken for at least 6 months each year. Prevention is safe and easy.

Our Wellness Plan for Cats includes annual and six-month health checks. We also carry a full line of parasite prevention products to protect your pet from heartworm and other common parasites.