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The Dangers of Heartworm

Drs. Foster & Smith Educational Staff
Dewormer Comparison Chart 
Dog Deworming Guidelines 
Heartworm Disease: Signs, Treatment, Prevention 
Heartworms are transmitted by mosquitoes that have bitten heartworm-infected animals. Heartworms spend their adult life in the right side of the heart and the large blood vessels connecting the heart to the lungs.

Heart illustration showing the heartworms in right ventricle and pulmonary artery What are the DANGERS of heartworm infection?
The adult heartworms can obstruct the different chambers of the heart and the various large blood vessels leading from the heart to the lungs. First, the right pumping chamber (right ventricle) of the heart and the large pulmonary artery leading from it to the lungs become enlarged as the worms take up space. If worms die, they may follow the flow of blood into smaller vessels in the lung and obstruct those vessels, causing pulmonary embolisms.

In severe infections, the worms can also block the large vein (vena cava) bringing blood to the right side of the heart. As the blood backs up, the liver becomes enlarged and damaged.

What are the SIGNS of heartworm infection?
Dogs with heartworm infections may show no signs at all, or they may have decreased appetite, loss of weight, and listlessness. Often, the first sign of the disease is a cough. Animals with heartworm disease will start to show lack of endurance during exercise. In severe cases, they may accumulate fluid in their abdomen (ascites) that makes them look pot-bellied. In rare situations in which animals have many adult worms, the animals may die of sudden heart failure.

Mosquito, carrier for heartworm infection
Heartworms are found in:
Dogs, Cats, Ferrets, Horses, Wild Animals (Bear, Fox)
Can humans be infected with heartworms?
Yes, there have been instances of heartworm infection in people. Instead of migrating to the heart, the larvae migrate to the lungs in humans. There the larvae can block vessels causing an infarction. At the site of the infarction, a nodule develops which can be seen on radiographs (x-rays). Usually, the person has few, if any signs of infection. Surgical removal of the nodule is sometimes necessary.

Did You Know?

  • Thousands of dogs die each year from complications relating to heartworm disease.
  • Heartworm is a disease that every dog can contract.
  • One bite from an infected mosquito is all it takes for your pet to become infected with heartworm.
  • Heartworm is almost 100% preventable.

Products to PREVENT heartworm in your dog...
Commonly used heartworm preventives for dogs include Heartgard Plus and Tri-Heart Plus.


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