Video: "Heartworm Disease" (3:00)—Dr. Scribano talks about how pets get heartworms, their effects, and how we can help prevent them.
Featured Quote: "The oral once a month prevention methods are good, but they're only good if you give it every single month and most of us are human, not superhuman."
The only way a pet can contract heartworm disease is from a mosquito bite. After a mosquito bites an infected animal, the tiny young of the heartworm are ingested with the animal’s blood into the mosquito, where they become infective larvae (capable of causing heartworm disease). When the mosquito bites another dog, the infective larvae enter the pet through the bite wound.
Infective larvae then grow over the next 6 months into adult heartworms, taking up residence in the dog’s heart, lungs, or arteries. This is heartworm disease. It can cause heart failure, lung disease, damage to other body organs, and eventually death—even sudden death with no apparent symptoms of the disease. Also, immature heartworms can cause the death of a pet if preventatives are not administered under the care of a veterinarian, because young worms in the bloodstream can suddenly die from the medication and trigger heart or respiratory failure.
The number of adult heartworms inside a dog can vary dramatically, but some studies indicate 15 worms on average. This is a population of both males and females, which reproduce more heartworms. One blood test can detect microfilaria, which are young worms inside a dog’s circulatory system that are the result of adult heartworm infection. This test is not very sensitive for heartworm disease. The most commonly performed test detects the presence of adult female worms by testing a dog’s blood for specific antigens. If tests are positive, preventive measures should not be started until the existing disease is treated by your dog’s veterinarian. As mentioned above, preventatives can cause complications in an already infected pet.
Treatment for heartworm disease is possible through drugs administered by your veterinarian. One medication contains melarsomine, a chemotherapeutic drug related to arsenic, and kills the adult worms that infect dogs. In advanced heartworm disease, the only treatment may be surgical removal of the worms, but full recovery is rare because serious damage to internal organs has already occurred.
Treating heartworm disease is a hardship, both on your precious dog and your finances. That is why we recommend annual testing for heartworms while your dog is on regular heartworm prevention. Many medications are approved to prevent heartworms in dogs. Options include topical, oral, and injection; all must be either prescribed or administered by a veterinarian. If you want to prevent more than just heartworms, there are some preventatives that also protect against fleas, ticks, and intestinal worms. Please talk to your veterinarian about which option is best for your pet.
Heartworm prevention does not eliminate adult worms, nor does it address the symptoms and damage that adult heartworms cause. That is why any existing heartworm infection should be diagnosed and treated by your veterinarian before your dog’s heartworm prevention is started. Regular tests should be performed after prevention has begun—annually, as recommended—to determine whether the dosage of prevention is adequate for your pet’s unique, ever-changing circumstances.
Owners may not notice symptoms of heartworm disease in their dog for months or years after infection. By the time that dogs show signs of heartworms, there is often advanced heartworm disease present. Much of the damage caused by heartworm infection is not reversible by the time signs are evident. If the disease has progressed far enough, it may be too late to start life-saving treatment. Symptoms of heartworm disease in dogs relate to the severity of the disease:
Class 1 heartworm disease is characterized by no visible symptoms at all, or by only minimal symptoms like occasional coughing. Class 2 heartworm disease is indicated by coughing and by fatigue after moderate exercise. In Class 3 of the disease, dogs begin to appear sickly, with loss of weight and muscle; coughing is persistent and fatigue occurs after mild activity; breathing is labored and heart failure can occur. Class 3 can be fatal if left untreated.
Class 4 heartworm disease has its own name: caval syndrome. The population of heartworms has grown so large in caval syndrome that blood can no longer flow freely into the heart. The only clinical option is surgical removal of the worms, a risky procedure that cannot undo the damage to the heart and lungs. Most dogs do not survive Class 4 of the disease even after surgery. The main goal of treatment for caval syndrome is to provide comfort for the pet.
As indicated above, prevention of heartworms is paramount. Please let the veterinarians at Northeast Animal Hospital help your dog stay free of these dreadful parasites.