Vet Blog

Watch Out for Worms: Heartworm Disease and Prevention for Pets

April 10, 2023

Although you've likely heard of heartworm disease, you may not know much about this parasitic condition.

Our Stone Ridge Veterinary Medical Center team sheds light on the importance of protecting your four-legged friend from this mosquito-borne threat, which can be fatal if left untreated.

Transmitting Heartworm Disease to Pets

Heartworm disease is a unique parasitic condition. To complete their life cycle, heartworm larvae (i.e., microfilaria) must pass through the mosquito. When a mosquito takes a meal from an infected animal, they ingest microfilaria, which develop to the infective larval stage in the mosquito's stomach. When the infected mosquito then bites a pet, they deposit larvae in the bite wound. The larvae wriggle their way under the skin, through the body's soft tissues, and eventually wind up in the pulmonary artery. During this migration, which takes about six months, the larvae mature into adults, at which point they begin reproducing more microfilaria.

Remember, heartworms can infect any mammal, including cats. However, heartworms prefer to reside in canine hosts. Heartworms thrive in dogs, living an average of five to seven years, and multiplying to reach a population in the hundreds. Heartworms only live two to three years in cats, and a single heartworm may be all that infects a cat.

Identifying Heartworm Disease in Pets

Until your pet is tested for heartworm, you likely will not know they have this disease. Signs can gradually develop over months or years, and some pets may show no signs.

Dogs affected with heartworm disease will typically first develop a nonproductive cough that worsens over time. They may also become exercise intolerant or fatigue after only moderate activity. An infected dog may lose their appetite, but develop a large belly, which is abdominal fluid accumulation caused by heart failure. Without treatment, the heartworm population inside your dog can increase enough to impede blood flow in and around their heart and lungs, ultimately causing your furry companion's death.

Cats affected with heartworm disease can show signs that appear similar to asthma, such as coughing, wheezing, and difficulty breathing. In some cats, the first and only heartworm disease sign is sudden collapse or death. Additional signs vary and include:

  • Incoordination while walking
  • Blindness
  • Vomiting
  • Inappetence and weight loss
  • Fainting
  • Seizures

Diagnosing Heartworm Disease in Pets

Diagnosing heartworm disease in pets can be a challenge, as in-clinic screenings typically only test for adult female heartworms' presence. If the following situations occur, the test will be falsely negative:

  • The heartworms are too immature.
  • The heartworms are all male.
  • Too few adult female heartworms are present.

Because of the incidence of false negative results, annual testing is important for detecting heartworm disease in its earliest stages, leading to early treatment, which can minimize permanent damage.

Treating Heartworm Disease in Pets

Your dog's heartworm disease treatment can be an unpleasant experience and potentially cause fatal side effects. A dog infected with heartworms must undergo a series of injections administered deep into the lumbar muscles. The injected arsenic-based compound can make your dog feel nauseated and sore. Your veterinarian will administer an initial injection and two additional injections, given 24 hours apart. During the entire treatment period, plus an eight-week recovery, you must keep your dog calm and quiet. To minimize your dog's potential side effects, such as an anaphylactic reaction to dying worms, or a vascular clot formation, strict exercise restriction is essential.

Although dogs' heartworm disease treatment is complex, no treatment exists for cats. Because no approved heartworm disease treatment for cats is available, your veterinarian can only provide your feline friend with supportive care for their associated signs.

Preventing Heartworm Disease in Pets

Fortunately, you can easily prevent your pet from contracting this deadly disease. Heartworm preventives are available in oral, topical, and injectable forms, and can also protect your pet against fleas, ticks, mites, and intestinal parasites. Your pet's most effective heartworm prevention is the product you actually feel comfortable giving them year-round.

Heartworm disease is a potentially fatal condition that you must take seriously. Ensure you protect your pet from this deadly threat by administering their heartworm preventive medication year-round. Contact our Stone Ridge Veterinary Medical Center team for guidance on choosing the best preventive option for your four-legged friend.