Heartworm disease is a sneaky and deadly threat to dogs and cats. If you’re not protecting your pet with year-round heartworm prevention, they’re at high risk for this heartbreaking condition.

To help ensure you have the information you need—and your pet gets the protection they deserve—the Creature Comforts Veterinary Service team has distilled the most important information you need to know about heartworm disease down to five essential facts. 

#1: Heartworm disease is deadly but preventable

According to the American Heartworm Society, more than one million pets in the United States have heartworm disease. On a more local level, 1 in 200 dogs are diagnosed in Pennsylvania every year. Because asymptomatic cats are less likely to be tested, their numbers are harder to determine, but some experts believe their numbers are likely on par with canine data. 

Heartworm disease is transmitted by mosquitoes infected with Dirofilaria immitis, a microscopic parasite transmitted by mosquitoes. When an infective mosquito bites and feeds on a pet, heartworm larvae (i.e., microfilariae) enter the pet’s tissues through the bite wound. Over time, the larvae migrate toward the lungs and heart where they mature, and create a cascade of inflammation and vascular damage that leads to multiple life-threatening problems, including:

  • Heart failure
  • Vessel blockages 
  • Respiratory distress
  • Sudden death

#2: Dogs and cats experience heartworm disease differently

Dogs are a natural host for heartworms, meaning that microfilariae can complete their remaining life cycle—including reproduction—inside the dog. Cats are not natural hosts, which can result in abnormal infections (e.g., worms migrating to other body areas), and unusual clinical signs, and make diagnosis a challenge. Most importantly, cats and dogs  differ in disease expression.

  • Dogs — In dogs, once heartworms reach maturity, signs are typically associated with heart failure, including:
    • Persistent cough
    • Exercise intolerance
    • Vomiting
    • Respiratory distress
    • Appetite loss
    • Swollen abdomen
  • Cats — Feline heartworm disease is more difficult to recognize, and infected cats may show no signs at all. Clinically affected cats may experience heartworm associated respiratory disease (HARD), an inflammatory condition that often is mistaken for feline asthma. Feline heartworm disease signs can include: 
    • Respiratory distress
    • Loss of coordination
    • Seizures
    • Collapse

Also, tragically, cats often show no visible signs before they die suddenly, with no explanation.

#3: Year-round prevention is essential for pet protection

Fortunately, heartworm disease is completely preventable. Keeping your pet, including indoor pets, on a year-round heartworm prevention plan can ensure that microfilariae don’t mature into dangerous adult worms. Because mosquitoes must bite and feed to transmit heartworm larvae, preventives work retroactively, killing any microfilariae circulating since your pet’s last dose. Because preventives work this way, one missed dose can leave your pet vulnerable to infection, since the next medication dose will not be effective against the microfilariae that have moved on to their next life stage.

Also, do not delay or postpone your pet’s preventives during the winter. Mosquitoes often come out on mild days, or overwinter in your garage or basement, and can infect your pet during the so-called off-season.

#4: Heartworm disease treatment is costly for dogs, and nonexistent for cats

Treating your pet only when they test heartworm-positive can be dangerous and life-threatening. For dogs, heartworm disease treatment is painful, lengthy, and expensive. Your dog will require up to three injections spread out over several weeks or months, additional testing, and medication. Also, you must keep your dog calm and restrict any exercise during the months-long treatment period to prevent a blockage caused by the dying worms.

Unfortunately for cats, no safe treatment is available for heartworm disease. Heartworm-positive cats can be treated only for their clinical signs, in hopes that they outlive the adult heartworms, which may survive up to two years.

#5: Annual testing is key to ensuring your pet’s prevention plan is effective

Pet owners often wonder why we recommend yearly heartworm testing for their pet who is receiving heartworm prevention, but testing, despite seeming redundant, is necessary to ensure your pet’s monthly medication is working effectively. Heartworm tests can be invaluable for several reasons, including:

  • Missed doses — Your pet’s heartworm test is essential if you’ve forgotten, postponed, or delayed a preventive dose .
  • Breakthrough infections — Although rare, some Dirofilaria immitis strains are now showing resistance to older heartworm disease preventives.
  • Tick-borne diseases — Our heartworm test conveniently screens for additional tick-borne diseases, such as Lyme, anaplasmosis, and ehrlichiosis, which can be subclinical (i.e., hidden), and early identification can speed treatment and prevent unnecessary suffering. 

Heartworm disease is a serious threat, but prevention is safe, effective, and convenient. Take action to protect your pet today by contacting Creature Comforts Veterinary Service to schedule your pet’s heartworm test, discuss their current heartworm prevention plan, or to formulate a new plan.