You reach for the box of monthly heartworm preventives for your dog and cat, only to realize that you used the last dose last month. As you throw the empty box in the trash, and think about the current state of your bank account, you wonder if heartworm disease really is a big deal, and whether you need to purchase more preventive. Surely, waiting a few months, or maybe skipping it entirely, will be OK. Right? Wrong! Read on to discover why heartworm disease should be taken seriously.

Heartworm life cycle in pets

Heartworms can be transmitted to your pet through the bite of a mosquito that has previously ingested the larvae, while feeding on the blood of an infected dog. Heartworm larvae deposited in your pet from the mosquito bite will continue to develop in the tissues over several months, before heading to their new home in one of the main heart arteries and right heart chambers, and developing to adulthood. The adult worms can live in a dog’s heart for five to seven years, and a cat’s heart for two to three years, causing substantial damage, not only while alive, but also after they die. In dogs, adult heartworms release larvae into the bloodstream that can be picked up by a mosquito, and transmitted to another pet, but cats do not have significant larvae circulating in the blood. 

Signs of heartworm disease in pets

Cats are relatively resistant to heartworms compared with dogs, and typically harbor fewer adult worms, but they can still become severely sick, or die, from heartworm disease. Some cats may not show any disease signs, while others may show signs such as:

  • Difficulty breathing, or asthma attacks
  • Coughing
  • Periodic vomiting
  • Lack of appetite
  • Weight loss
  • Collapse, or sudden death

Dogs with heartworm disease may show no signs in early infections, but as the worms damage the heart and lungs, you may notice:

  • Coughing
  • Lethargy
  • Rapid fatigue, or unwillingness to exercise
  • Enlarged abdomen due to fluid accumulation
  • Difficulty breathing
  • Collapse, or sudden death

Testing your pet for heartworm disease

All dogs 7 months and older should be tested yearly for heartworm disease, including those on year-round preventive, because dogs can spit out, or vomit, a dose without you noticing, or you could accidentally forget a dose, and one missed dose can lead to a heartworm infection. Any new dog, or one who has not been on preventive consistently, should be tested initially, and then retested in six months, because the heartworm test indicates the presence of adult female worms only, and dogs with larvae or juvenile worms at the time of testing would not show up as positive for heartworms. 

Cats are not routinely tested for heartworms, but if we suspect your cat has heartworm disease, we will use several tests, such as heart and lung imaging, the canine test that detects the presence of adult female worms, and/or a test looking for worm exposure. This combination approach is needed, because some cats have only male heartworms, may have been exposed and cleared the infection, or may have only juvenile heartworms at testing time, thus complicating the heartworm disease diagnosis. 

Prevention of heartworm disease in pets

All pets, including indoor pets, should receive heartworm preventives year-round for best protection. In fact, the American Heartworm Society reports that 25% of feline heartworm disease cases were indoor-only cats, so staying inside isn’t adequate protection. Heartworm preventives work retroactively, and kill young larvae acquired the previous month, while older larvae and adult worms are not killed by typical heartworm preventives. So, giving your pet heartworm preventives each month, to prevent the young larvae from developing into dangerous adults that can damage your pet’s heart, and from being transmitted to other pets by a mosquito bite, is critical. For added protection, select an external parasite preventive that also repels mosquitoes, treat your yard for mosquitoes, and eliminate areas where mosquitoes like to breed.

You may be tempted to cut heartworm preventives from your budget, especially in the current economic climate, but remember—preventing heartworm disease costs significantly less than treatment. In addition, heartworm disease could permanently damage your pet’s heart and lungs, or cost her her life. 

If you need to start your pet on a heartworm preventive, your dog is due for a heartworm test, or you are running out of preventive, contact our Noah’s Ark Veterinary Hospital team. For questions regarding heartworm disease, feel free to call our team, or consult the American Heartworm Society website.