Your veterinarian has diagnosed your dog with heartworms, but he doesn´t act sick and you´re concerned by the high cost and possible danger of the treatment. You´re thinking about not treating his heartworms at all. That may not be the best idea, and here´s why.

I know how costly and dangerous the treatment is, but I strongly encourage you to follow your veterinarian´s advice and have your dog treated as soon as possible before the disease progresses to the point it cannot be treated. The longer your dog has had heartworms, the greater number of adult worms he will have in his heart and lungs.

Your dog most likely became infected through the bite of a mosquito that transferred a microscopic larvae or microfilaria, from an infected animal. The larvae migrated through your dog´s tissues and bloodstream, ending up in the heart where they grew into adult worms, reproducing more microfilaria in about 6 months.

Your dog will not show signs until he has been infected for about a year, and the first outward sign of infection is usually soft coughing. As the disease progresses, your dog will find it more difficult to breathe, may be reluctant to exercise, may lose his appetite and weight. After 5–7 years of infection with heartworms, massive numbers of long thin adult worms (resembling vermicelli) will clog the heart and major blood vessels to the lungs, usually causing death from congestive heart failure and other organ failure.

Prevention is easy. There are daily and monthly oral preventives; and monthly topical preventives. Many of these preparations contain medications that will also kill intestinal parasites. A simple blood test can diagnose heartworms and your pet should be checked before starting any preventive. Puppies can be started on preventives without being tested.

Sharon E. Anderson, DVM

Sharon E. Anderson, DVM, answers medically-related questions, but will not attempt to diagnose or recommend specific treatments. Her advice is not meant to replace professional care. If your pet is ill, contact your veterinarian immediately.