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Heartworm Disease

Heartworm Disease is a potentially life-threatening parasitic infection. Found worldwide, it infects wild and domestic dogs, sea lions, ferrets, and cats. In rare cases it can infect other animals and humans.

How Pets Get Heartworms
Heartworm Disease is caused by a worm, Dirofilaria immitis, and spread by mosquitoes. When a mosquito feeds on an infected animal, usually a dog, it ingests microscopic larvae in the blood. These microfilaria mature in the mosquito for about two weeks. When the mosquito bites a susceptible animal, the infectious larvae are transferred into its tissues. They migrate through the animal's body, maturing into adult worms over a period of months. The adult worms live in the heart and major blood vessels where they reproduce to create new microfilaria. The time from infection to appearance of microfilaria is about six months.

Dogs are highly susceptible to heartworm infection while it is much less common in other domestic animals such as cats and ferrets. In the United States, heartworms are found in all 50 states but are most common along the Atlantic and Gulf coasts and near the Mississippi River.

What the Disease Does
The severity of the disease is related to the number of adult worms present. Adult worms cause inflammation of the blood vessels and the lungs. The disease can progress to heart failure, liver failure, and rupture of major blood vessels. Dogs with heartworms do not always show symptoms, especially in the early stages of the disease or if only a few adult heartworms are present. When symptoms do occur, they include coughing, tiring easily during exercise, difficulty breathing, fluid in the abdomen, fainting, and death.

How Heartworm Disease is Diagnosed
Adult heartworms can be detected with a simple blood test. Pets that test positive should undergo additional testing to determine the stage of the disease. Recommended procedures include a blood screen for microfilaria and chest x-rays. Prior to initiating treatment, dogs should have a complete blood panel. EKGs, echocardiograms, and angiograms may also be recommended.

Treatment for Heartworm Disease
Dogs are treated with drugs that are able to kill the adult heartworms, but are also potentially fatal for the dog. Therefore, treatment is performed in the hospital where the dog can be carefully monitored and treated for toxicity if necessary. Treatment may need to be repeated more than once, and can be quite costly. Dogs that initially test positive for microfilaria undergo a second stage of treatment. Treatment for microfilaria is not as dangerous and is usually given on an outpatient basis, three to six weeks after treatment for adult worms. Successful treatment is confirmed by testing again for adult worms and for microfilaria.

Preventing Heartworm Disease
Fortunately, effective preventive medications are available to protect dogs. Puppies can be started as early as 4-6 weeks of age. Annual retesting for heartworm is recommended. Preventive medication is given seasonally in some parts of the U.S., but year-round in temperate regions. If a dose is missed, it's best to give it as soon as possible and check with your veterinarian about the need for a heartworm test.

Heartworm Prevention Products

  • Iverheart Max – Prevents heartworm and treats intestinal parasites, including tapeworm.
  • Heartgard Plus – Prevents heartworm and treats intestinal parasites, not including tapeworm.
  • Proheart 6 – Injectable heartworm medication that prevents heartworm infection for 6 months.

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