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Heartworm Disease

Heartworm disease in a potentially fatal disease of dogs and cats caused by a blood-borne parasite transmitted by mosquitoes. A mosquito bites a dog or and injects small heartworm larvae in the skin of the pet. Each bite can transmit 5-10 larvae into the dog or cat. Wow! Over the next seven months these worms migrate and mature to become adults in the right side of the heart and vessels of the lungs and heart. At this point the Heartworms reproduce to become microfilaria or baby worms which circulate in the animal’s blood stream to be picked up by a biting mosquito. The microfilaria undergoes a development process in the mosquito and can subsequently be transmitted to another dog or cat when the mosquito next feeds. The infestation in the heart and lungs can lead to tremendous inflammation and obstruction of blood flow to the lungs. This results in coughing, exercise intolerance, weight loss and even right-sided heart failure and death. Infestations are often advanced before signs are seen. The cat’s body often reacts differently than the dog. The cat’s immune system starts to destroy the immature worms as they arrive in the heart and lungs. The subsequent inflammation leads to a difficulty breathing producing an asthma-like episode.

The good news is heartworm disease is very preventable with monthly medication . These are medications which kill the larval worms which are initially injected into the dog and cat’s skin by the mosquito. The heartworms never have the chance to mature to adult heartworms. At that point, they are resistant to the effects of the heartworm prevention medications. All dogs should be tested for surveillance yearly as some heartworm preventions can be harmful to the dog if mature heartworm disease is present. There is no effective test in cats but the heartworm products for cats are safe regardless of the cat’s heartworm status. Once a dog has mature heartworms, the dog must be treated with a series of injections over a couple of months of an arsenic-related drug to kill the worms. The treatment is expensive and many dogs have treatment complications. There is no treatment in cats and infections often are eventually fatal. Heartworm disease is endemic in all 50 states. Because a dog or cat is indoors does not make it safe. Mosquitoes can easily enter homes and bite at night or bite the pet when it is outdoors to eliminate. Therefore it is recommended that all dogs and cats should be on monthly heartworm prevention as a part of wellness care.

- Dr. LaRoche

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