In 2001, more than 244,000 dogs in the U.S. tested positive for heartworms.
What is heartworm?
Heartworms belong to the same class of worms as roundworms. Adult heartworms produce very tiny larvae which can live up to three years in a dog's blood stream. When a mosquito sucks blood from an infected animal it also sucks up larvae and transmits it to other animals. The larvae live in the animal's skin until it gets bigger and moves to the heart where it continues to grow. It takes about 6 months between the time the animal is bitten until the larvae moves to the heart. Severely infected dogs can have up to several hundred heartworms in their hearts and vessels.
What does a heartworm do?
The worms block the heart chambers as well as the blood vessels in their search for an oxygen rich blood supply. If the larvae or worms die, they can flow through the animal's blood system and block blood vessels along the way, including those in the lungs.
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.
Signs and Symptoms of Heartworm
Lethargy - lack of endurance during exercise
Coughing - sometimes with blood
A history of not receiving heartworm preventative medicine
Decreased appetite
Loss of weight
Some will accumulate fluid in their abdomen that makes them look pot-bellied
Vomiting
Blindness
Seizures
Detecting Heartworm
Blood tests detect most cases of heartworm. In rare cases, heartworm infections can occur without the larvae in the bloodstream. This occurs if only male worms are present or if the females are not laying larvae at the time of the test. There are special tests designed to detect heartworm if this is the case. Most cases are detected early in a routine exam and can be treated successfully.
Prevention
Dogs should be placed on heartworm preventative medicine on a schedule prescribed by your veterinarian. Daily and monthly forms of medication are available. Heartworm preventative medication should not be given until the dog has been tested. These medications will not kill the adult worms, only the growing larvae. Special medicines will kill the adult worms. Like all medications, follow the recommendations and guidelines of your veterinarian and the manufacturer of the drug. Check with your vet for the best drug to use.
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