Heartworm Disease in Dogs

Cost of Treatment: $173.00 to $301.00

What is Heartworm Disease in Dogs?

Canine heartworm is a serious disease caused by a parasitic worm called Dirofilaria immitis, which lives in the lungs, heart and associated vasculature of an infected animal. Mosquitoes spread heartworm disease. When a mosquito bites an infected dog, it becomes infected with the immature form of the worm (microfilariae). Microfilariae become infective larvae inside the mosquito and when the infected mosquito bites another dog transmission occur. Inside the infected dogs larvae become adults, reproduce and the offspring go to the blood.

The U.S. FDA defines four stages of canine heartworm disease:

  • Class 1:  No symptoms or mild symptoms (e.g. occasional cough).
  • Class 2:  Mild to moderate symptoms (e.g. occasional cough and fatigue moderate activity). Heart and lung changes are usually seen on chest x-rays.
  • Class 3: General loss of body condition, a persistent cough, and fatigue after mild activity.  Heart and lung changes are usually seen on chest x-rays.
  • Class 4:  A large mass of heartworms prevents blood from flowing back to the heart causing a cardiovascular collapse known as Caval syndrome.

Symptoms of Heartworm Disease in Dogs

  • Mild persistent cough
  • Reluctance to exercise
  • Fatigue after moderate activity
  • Decreased appetite
  • Weight loss
  • Heart failure and the appearance of a swollen belly (due to excess of fluid in the abdominal cavity).
  • Sudden blockages of blood flow within the heart (Caval syndrome), characterized by labored breathing, pale gums and dark bloody or coffee-colored urine.

Treatment for Heartworm Disease in Dogs

  • Ivermectin: this is the main ingredient of many heartworm preventive products and it is capable of killing microfilariae. Usually, infected dogs are administered a microfilariae-killing drug to prevent them from developing into adults and then an adult-killing drug is administered.
  • Milbemycin: is also found on heartworm preventive products (e.g. Sentinel and Interceptor) and can kill the microfilariae much faster than ivermectin. This can be disadvantageous because large numbers of microfilariae dying at the same time can cause a circulatory shock.
  • Melarsomine dihydrochloride (Immiticide® by Merial): is the only FDA approved drug to kill adult worms. Treatment consists of two or three deep injections into the back muscles. These injections are very painful so your dog may also need pain.

Resources for Heartworm Disease in Dogs

  1. FDA: Facts About Heartworm Disease
  2. The American Heartworm Society

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