Heartworms in Dogs 

Heartworms are a parasite called Dirofilaria immitis, which is a type of roundworm. Heartworm disease in dogs is defined as an infestation of parasites living in a dog’s heart and lungs. Any breed of dog can become affected with heartworms, but this occurs most commonly in dogs 3-6 years old. Heartworm disease does occur in cats, but not as commonly. Heartworms are spread to dogs through the bite of a mosquito that is carrying the infective heartworm larvae. The mosquito that carries heartworm disease is found in highest numbers in the southeastern United states, Northern California, Oregon, and Washington, but heartworm disease has been reported all over the United States.

Once the mosquito bites, the larvae migrate from the bite wound through the dog’s body until they reach the heart and blood vessels of the lungs and become adults. This whole process usually takes 6 months. 

Symptoms in dogs suffering from heartworm disease can range from mild to severe. Dogs can display no clinical signs, occasional cough to frequent severe cough, collapse, difficulty breathing, weakness, lethargy, and inability to exercise.  The severity of clinical signs seen in dogs depends on the number of adult worms present, the location of the worms, the amount of time the worms have been in the dog, and the amount of damage the worms have created within the body. Clinical signs can worsen causing heart failure or death of your pet during excitement or exercise. Risk factors that make heartworm contraction more likely are dogs that live in heavy heartworm areas, are outdoors often or live outdoors only, and are not on routine heartworm prevention.

If your veterinarian suspects heartworm disease, several tests will be performed to diagnose heartworm disease such as bloodwork, X-rays, and in some cases advanced imaging of the heart and lungs. Treatment of heartworm disease can be dangerous, costly, and may take a very long time. Treatment of heartworm disease is based on the severity of each case and the secondary complications that have occurred from the heartworms themselves. Any secondary complications such as heart failure must be treated and managed first. In order to kill the adult heartworms present in your dog, an injectable drug is given multiple months apart in addition to other medications. Hospitalization is required following these injections so dogs can be monitored for post-treatment complications, which can be fatal. Complete exercise restrictions are required for several weeks to months after injectable treatment is administered. This is necessary because as adult worms die and are broken down by the body; pieces of the worms can lodge in small blood vessels and cause problems. Dogs must be monitored closely for weeks to months for treatment reactions such as loss of appetite, shortness of breath, coughing, and lethargy. Prognosis varies based on the severity of each case and secondary complications that have occurred. 

The most important aspect of heartworm disease is prevention. Routine, year round, heartworm preventatives will keep your pet safe from contracting this life-threatening parasitic infection.  Please contact your Veterinarian for more information on preventative options. If your dog is showing clinical signs of heartworm infestation, please have your pet evaluated by a veterinarian as soon as possible.