April is Heartworm Awareness Month


April is Heartworm Awareness Month.  Is your pet heartworm free? Dogs are considered the definitive host for heartworms (Dirofilaria immitis). However, heartworms may infect more than 30 species of animals    (e.g., coyotes, foxes, wolves and other wild canids, domestic cats and wild felids, ferrets,  sea lions, etc.) Feline heartworms are more deadly and difficult to treat.

Heartworm (Dirofilaria immitis) is a parasitic disease.  This severe and sometimes fatal disease is transmitted to your pet by the bite of a mosquito infected by the heartworm. When an infected mosquito bites an animal, the heartworm larvae migrate through the broken skin and into the circulatory system. The larvae develop into sexually mature adult heartworms over the next 6-7 months. Female adult heartworms can reach up to 10-12cm in length! The heartworm lifespan is 5-7 years. As the name implies, adult heartworms reside in the cardiac [heart] and pulmonary [lung] vasculature. Adult female heartworms produce microfilariae (juvenile heartworms) and release them into circulation. These microfilariae act as a reservoir and can then be picked up by mosquitoes that bite an infected animal.



Heartworm disease is preventable with the administration of a heartworm prophylaxis (preventative) medication, as recommended by a veterinarian. For those dogs that do contract heartworm disease, the prognosis is good for mild to moderate cases, and such conditions can be relatively uneventful. Dogs with more severe cases may suffer from lung complications resulting from extreme medication given to kill serious infestations.

Symptoms and Types:

[stextbox id=”alert” color=”000000″ bgcolor=”b591a5″]Heartworm disease is defined in three classes, varying in severity. Dogs with Class I heartworm disease are often asymptomatic, meaning they exhibit no visible symptoms, or may only exhibit minimal signs such as an occasional cough. Class II patients usually exhibit coughing and unusual intolerance to exercise. The most severe cases, defined as Class III, may show symptoms of anemia, exercise intolerance, fainting spells, and — in severely affected dogs, right-sided chronic heart failure.

  • Lethargy
  • Coughing
  • Labored breathing
  • Weakness
  • Syncope (temporary loss of consciousness)
  • Abnormal heart and lung sounds
  • Ascites (fluid accumulation in the abdominal cavity



When some dogs are diagnosed, they have advanced heartworm disease. This means that the heartworms have been present long enough to cause substantial damage to the heart, lungs, blood vessels, kidneys and liver. A few of these cases will be so advanced that it will be safer to treat the organ damage rather than risk treatment to kill the heartworms. Dogs in this condition are not likely to live more than a few weeks or months. Your veterinarian will advise you on the best treatment approach for dogs diagnosed with advanced heartworm disease.

  • katsrus

    Thank you for the post.
    Sue B