Virginians are accustomed to swatting mosquitoes when the weather is nice, but these pesky bugs can cause more than an itchy welt for your pet. Our Town & Country Animal Hospital team wants to protect your pet’s heart from parasites, and we offer information about heartworms and explain what you should do to protect your four-legged friend.

Coyotes, foxes, and raccoons–oh my!

Wildlife, such as coyotes, foxes, and raccoons, and unprotected domestic dogs are natural hosts for heartworms and serve as reservoirs for infection. Having one infected raccoon pilfering your garbage or one unprotected dog in your neighborhood significantly increases your pet’s risk of heartworm infection. Let’s look at how the parasite can get from these animals into your vulnerable pet.

  • A mosquito gets hungry — When a mosquito takes a blood meal from an infected dog or wild canid, they ingest microfilariae (i.e., baby heartworms). 
  • Heartworms grow — While inside the mosquito, the young heartworms mature to an infective larval stage, which takes about three weeks. When the larvae are ready, they travel to the mosquito’s salivary glands where they can be transmitted.
  • The mosquito transmits heartworms — The next time the mosquito feeds on a pet, the infective larval heartworms are deposited on the pet’s skin and swim through the bite wound to cause infection.
  • Heartworms take a trip — The larvae migrate to the pet’s heart, lungs, and associated blood vessels where they make themselves at home.
  • Heartworms grow their family — When inside a natural host, heartworms can mature to adulthood, mate, and produce offspring (i.e., microfilariae) to provide another infection source.

As different as dogs and cats

Dogs and cats have little in common, and this includes their response to heartworm infection. Since dogs are natural hosts, the parasites find a welcoming environment in which they thrive while parasitizing the dog’s heart. Worms can reach up to 14 inches in length, and numerous worms—as many as 100–can invade a single dog. However, the relationship doesn’t provide many benefits for the dog. When heartworms reach the blood vessels that supply the dog’s lungs, the animal’s immune system responds, leading to inflammation, which eventually causes fibrosis and thickening of these vessels. This creates a high tension area that inhibits the heart’s ability to effectively pump blood throughout the body, eventually leading to congestive heart failure (CHF).

Cats are atypical hosts for heartworms, which means the parasites that find their way into a vulnerable cat aren’t met with a warm welcome. The cat’s immune system responds aggressively, removing many of the larvae, but the cat doesn’t get away unscathed. When the heartworms reach the lung tissue, severe inflammation occurs, causing a condition called heart-associated respiratory disease (HARD). In addition, if one or two heartworms survive to adulthood, the parasites can cause devastating consequences for the cat’s tiny heart.

Your pet’s lips are sealed

You might think you would know if your furry friend has parasites invading their heart, but unfortunately, most pets don’t exhibit signs until their condition is advanced, putting their life at risk. When signs are present, they include:

  • Dogs — Lethargy, exercise intolerance, decreased appetite, a soft, persistent cough, and weight loss. When CHF develops, fluid starts to accumulate in their abdomen, and they may have a pot-bellied appearance.
  • Cats — Wheezing, open-mouthed breathing, increased respiratory rate and effort, and vomiting. In many cases, the first sign in cats is sudden death.

Hopefully, your pet will pass with flying colors

The American Heartworm Society (AHS) recommends that dogs be tested annually for heartworms. Diagnostics include:

  • Microfilariae test — In some cases, circulating microfilariae can be seen after the blood has been concentrated. 
  • Antigen test — Antigen tests detect a protein produced by the adult female heartworm. AHS current recommendation is for dogs to be tested using both the microfilariae and antigen test.
  • Antibody test — The antibody test evaluates a pet’s response to heartworm infection. These tests are useful for cats because cats typically don’t have circulating microfilariae or adult worms.
  • Imaging — Imaging techniques, such as X-rays and ultrasound, are also helpful when diagnosing heartworms.

Your pet needs more than a spoonful of sugar

Heartworm disease isn’t an easy condition to treat. No approved medications are available for cats, and treatment focuses on supportive care. In some cases, a cat can clear the young heartworms and outlive the adult parasites, but the damage caused to their lungs is irreversible, leading to ongoing respiratory issues.

While treatments are available for dogs, the medications can cause serious side effects, such as anaphylaxis and blood clots as the worms die off. In addition, dogs must be strictly confined during treatment because physical exertion exacerbates damage to the heart and lungs. 

Heartworm treatment is dangerous, prolonged, and expensive, and prevention is a much better way to address heartworms in cats and dogs.

An ounce of prevention is worth a pound of cure

Luckily, heartworms are easy to prevent. All pets, including those who only live indoors, should receive year-round heartworm prevention medication. “Why year round?” you ask. Because temperature fluctuations and unseasonably warm days can cause dormant mosquitoes to wake up and look for a meal. In addition, if you are a little too late starting your pet’s heartworm preventive in the spring or a little too early stopping it in the fall, they are at risk of infection.

Heartworm disease is no laughing matter, but keeping your pet on a year-round heartworm preventive and having your dog tested annually can protect your four-legged friend from these vicious parasites. Contact our Town & Country Animal Hospital team to schedule your dog’s annual heartworm test or to discuss what heartworm preventive is best for them.