Heartworm

There's a special place for you in your dog's heart. Unfortunately you have competition.

Heartworm is a very common parasite in southern Ohio. Heartworm is just what the name implies--an infestation of the right side of the heart and the pulmonary arteries with large worms, some up to six inches long. These worms can cause serious damage not only to the heart and lungs, but also to the kidneys and liver.

The life cycle of the heartworm begins when a mosquito ingests microfilaria from an infected dog. These larvae undergo two molts within the mosquito (taking 2 to 3 weeks), at which point the larvae are infectious when the mosquito bites another dog and injects the parasite. These infectious larvae migrate through the blood vessels to the lungs and pulmonary arteries. It takes 5-6 months before maturity, at which point the female worms release microfilaria into the host's bloodstream, and this dog becomes infectious to other dogs, by way of a mosquito. Clinical signs of heartworm disease include a cough, exercise intolerance, difficulty in breathing, and, in advanced disease, weight loss and abdominal distension.

Heartworm is detected either by finding microfilaria (filter test) or antigens from the female worms, both requiring a blood test. Both tests do not become positive until 4-6 months post infection (time to maturity). Microfilaria might be found in the bloodstream of young puppies (under six months of age), but these most likely represent microfilaria which have crossed the placenta, and will not grow to adult-hood.

Treatment of heartworm disease requires the use of drugs which can have serious side effects, and, as the worms are dying, they can fragment into smaller segments (worm emboli) and severely damage the lungs or even cause death. Obviously, the best treatment for heartworm disease is prevention.

Prevention of heartworm infestation is easily accomplished. Monthly medication is now available which kills the larval stage of the worm which is injected by the mosquito. Side effects of the heartworm preventative are extremely rare, and most veterinarians recommend that dogs remain on heartworm preventative year round, with blood checked yearly for evidence of infection. It is quite common for "indoor" dogs to become infected with heartworm, so it is extremely important for all dogs to be on heartworm preventative.

For those of you who own cats--feline heartworm infestation is becoming more common, and feline heartworm preventative is also available from your veterinarian.

We wish to thank Dr. Lee Schrader for agreeing to write this article for our newsletter. Dr. Schrader is a Diplomate of the American College of Veterinary Internal Medicine and practices at Suburban Animal Hospital in Dayton (937-433-2160). She is married to Dr. Steve Schrader who is a Diplomate of the American College of Veterinary Surgery, specializing in Orthopedic Surgery at the CARE center in Cincinnati (513-530-0911). Both Drs. Schrader are especially knowledgeable of the Great Dane breed. If you ever have a problem, we highly recommend them.

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