April is Heartworm Prevention Month and we want to ensure our Belmont Animal Hospital families understand the ins and outs of this deadly disease, including transmission, how to protect your pet, and treatment should your pet test heartworm-positive. Our team answers common questions about heartworm disease so you can keep your pet safe. 

Question: How do pets get heartworm disease?

Answer: Heartworms are transmitted primarily through an infected mosquito’s bite. Immature heartworms (i.e., microfilariae) enter your pet’s bloodstream through the bite wound and travel through your pet’s bloodstream, maturing into adult heartworms in approximately six months. The heartworms continue to grow—adult heartworms look like foot-long spaghetti noodles—and then reproduce infecting areas in and around your pet’s heart, lungs, and pulmonary blood vessels. Infected pets cannot pass heartworms to other pets, because a mosquito is necessary to develop the larvae to the “infective stage.”

Q: Is heartworm a serious condition in pets?

A: Yes. Heartworms can live inside your pet for five to seven years, leading to a wide range of health problems that, left untreated, can be fatal for your pet.

Q: Does heartworm affect only dogs?

A: While dogs are most at risk, any mammal can develop a heartworm infection, including cats and ferrets. Cats tend to be more resistant to heartworms than dogs, but they are still vulnerable, and because of their size, only a few worms can cause an infection, and be detrimental to their health. 

Q: Does heartworm disease affect dogs and cats the same way?

A: Heartworm disease appears differently in cats than dogs. Disease severity in dogs depends on the number of worms living inside their body—in some cases, several hundred—the time the dog has been infected, and their body’s response to the infection. Heartworm may not be obvious in dogs who have been recently infected, or are not active. Dogs who have been infected for a long time, or are extremely active, often will show obvious signs, including: 

  • Mild, persistent coughing
  • Reluctance to exercise
  • Fatigue after exercise
  • Decreased appetite and weight loss

Detecting heartworm infections is more difficult in cats. Most worms do not survive to the adult stage in cats, and not all cats with heartworm disease show signs. If cats do show heartworm signs, they may include:

  • Vomiting
  • Decreased activity 
  • Decreased appetite, and weight loss
  • Respiratory problems (e.g., trouble breathing, increased respiratory rate, and cough) 

Q: How is my pet checked for heartworm disease?

A:  Checking for heartworm disease requires a blood sample. Unfortunately, the in-house heartworm test will detect only adult female heartworms, so if only immature heartworms or adult males are present in your pet (i.e., a cat with only a few worms), they may receive a false negative result. If necessary for diagnosis confirmation, your veterinarian will send blood to an outside laboratory for more specific testing.

Q: Is treatment available for heartworm-positive dogs?

A: Yes. The earlier your dog receives treatment, the more likely a positive outcome. Treatment for heartworm includes:

  • Antibiotics — The first goal is to reduce the infection side effects and begin killing the worms.
  • Medications — Treatment in dogs involves injecting medication into the dog’s lumbar muscles, and can be extremely painful. Several injections spaced 30 days apart are often needed.
  • Exercise restriction  Exercise restriction during treatment, which can take months, is extremely important to reduce the risk of potentially fatal exercise-induced side effects caused by the dying worms lodging in and causing a blockage in the lungs.
  • Surgical removal — This may be an option in extreme cases to remove a pet’s heavy worm burden, but is seldom successful.

Q: Is treatment available for heartworm-positive cats?

A: Unfortunately, no treatment exists for heartworm disease in cats, whose first sign is often sudden death, making prevention essential.

Q: Can pets be protected from heartworm disease?

A: Yes. A variety of safe, effective heartworm prevention products are available in topical, oral, and injectable forms. While heartworm transmission from mosquitoes is less likely during the winter months, the risk is never zero and heartworm preventives should be given year-round. One missed dose of preventive can leave your pet vulnerable to infection. 

Other ways to reduce your pet’s risk of heartworm infection include:

  • Water sources — Remove standing water sources that could attract mosquitoes (e.g., flower pots, fountains, kiddie pools).
  • Windows and doors — Keep your window and door screens free from tears, to ensure mosquitoes can’t get inside your home.
  • Shady spots — Do not walk your pet in moist, shady areas where mosquitoes prefer to live.

Year-round heartworm preventives are the easiest way to keep your pet safe from heartworm disease. If your pet is due for their annual wellness checkup and heartworm testing, contact our team at Belmont Animal Hospital so we can ensure they are parasite-free.