Mosquitoes may be tiny, but they transmit a significant threat to pets—heartworms. These parasitic worms can wreak massive, irreparable damage on your pet’s cardiovascular system and potentially prove fatal. Learn the ins and outs of heartworm disease to ensure your four-legged friend’s safety from this parasitic condition.

The basics of heartworm disease in pets

Heartworm disease is caused by a parasitic worm known as Dirofilaria immitis and can affect any mammal, including dogs, cats, and people. While dogs and wild canines are the ideal hosts, heartworms can infect and reproduce in any mammal. These worms are transmitted when an infected mosquito carrying heartworm larvae (i.e., microfilariae) bites a dog or cat. The larvae enter the pet’s bloodstream and migrate to the heart, lungs, and surrounding blood vessels, where they develop into adult worms over six to seven months.

In dogs, heartworms can grow up to 12 inches in length and reach populations of 50 or more. Throughout their 5- to 7-year lifespan, heartworms can obstruct blood flow, leading to heart failure, pulmonary hypertension, and other life-threatening complications. 

In cats, heartworms are smaller in size and number, but they can still cause severe health issues, including respiratory distress, coughing, and sudden collapse. Immature heartworms, which can instigate a severe inflammatory reaction in the lungs that can prove fatal, are often the primary cause of respiratory issues in cats.

Heartworm disease signs in pets

Heartworm disease signs can take months or years to become apparent. They can differ between dogs and cats, and in cats, they primarily manifest as lung disease, causing:

  • Coughing
  • Wheezing
  • Gagging
  • Intermittent vomiting
  • Difficulty breathing
  • Sudden collapse
  • Convulsions
  • Sudden death

In dogs, heartworms more seriously damage the cardiovascular system, resulting in:

  • Persistent, progressive cough
  • Fatigue and weakness
  • Reduced appetite
  • Weight loss
  • Difficulty breathing
  • Abdominal enlargement caused by fluid accumulation

Heartworm disease diagnosis in pets

Heartworm disease is most commonly diagnosed through blood tests that detect the presence of proteins (i.e., antigens) produced by female adult heartworms. Since these in-hospital tests are highly specific, they can produce false negative results if no adult heartworms or female heartworms are present. Then, additional blood tests are needed to confirm heartworm presence, as well as imaging tests to assess the infection’s severity. 

Heartworm disease treatment for pets

Treating heartworm disease in pets is much more challenging than treating an intestinal worm infection. Dogs must be strictly exercise-restricted during their months-long treatment to avoid life-threatening complications. They will receive a series of arsenic-based injections administered deep into their lumbar muscles, which often causes discomfort and nausea. Most dogs need three injections.

No heartworm disease treatment is approved for cats. Their treatment is focused on managing clinical signs in hopes that their immune system will eradicate the heartworms.

Heartworm disease prognosis for pets

Heartworm disease can lead to serious complications, including heart failure, pulmonary hypertension, vascular and pulmonary clots, and organ damage. The prognosis for pets with heartworm disease depends on various factors, including infection severity, complications, and treatment response. Early detection and intervention offer the best chance for a positive outcome.

Heartworm disease prevention for pets

Prevention is key to protect pets from heartworm disease. Monthly heartworm preventives are available for dogs and cats and are highly effective in preventing heartworm infection. They come in various forms, including oral tablets, topical treatments, and injectable formulations, and all must be administered regularly and according to a veterinarian’s instructions. Additionally, minimizing exposure to mosquitoes by keeping pets indoors during peak mosquito activity times and using mosquito repellents can reduce infection risk.

Heartworm disease is a serious and potentially fatal condition that affects cats and dogs, regardless of the amount of time they spend outdoors. Regular veterinary visits, heartworm screenings, and heartworm prevention administration are essential components of your pet’s comprehensive healthcare regimen. Give our Santa Monica Veterinary Group team a call if you need help protecting your four-legged friend from heartworm disease.