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What Is Heartworm Disease?

Heartworm disease is a severe, life-threatening condition caused by a dog's reaction to a live parasitic worm infestation inside the dog's heart and pulmonary arteries (which carry blood from the heart to the lungs), preventing those organs from functioning properly. The result is severe lung disease, heart failure, other organ damage, and death.

How Dogs Get Heartworms
A dog gets heartworms when it is bitten by a mosquito that had previously bitten a dog carrying heartworms. Microscopic baby heartworms from the first dog get ingested by the mosquito when it sucks up some of the dog's blood. Later, those babies, which have matured to larvae within the mosquito, get transferred to the new dog when the mosquito bites. Inside the new dog, the tiny heartworm larvae then grow, mature into adults, mate, and produce offspring. Virtually 100% of unprotected dogs exposed to infective larvae through a mosquito bite become infected!

Image: New Rattitude, Inc. Rat Terrier Rescue & Adoption What Heartworms Do
Heartworms living in a dog's heart are typically 6-12" long and about the diameter of a piece of spaghetti. One dog may have as many as 250 worms! The worms survive up to five years and, during this time, the females produce millions of young (microfilariae). Adult worms cause disease by clogging the dog's heart and major blood vessels, interfering with the heart's valve action and reducing the blood supply to other organs of the body, particularly lungs, liver and kidneys, which leads to malfunction of these organs. The microfilariae circulate throughout the body and block blood flow in the small blood vessels, depriving the body cells of nutrients and oxygen. Destruction of the dog's lung tissue leads to a dry, chronic cough and shortness of breath. Liver problems cause anemia and general weakness and loss of stamina. Affected kidneys may allow poisons to accumulate in the body. The dog may show nervousness, listlessness, and exhaustion that is especially noticeable after exercise, when some dogs may even faint. Advanced cases progress to severe weight loss, coughing up blood, swelling of the abdomen and legs, and, finally, congestive heart failure.
        This is a horrific disease that no dog should have to endure. It is even more horrible because it is easily and inexpensively preventable.

What are the Symptoms of Heartworm Disease?
The amount of heartworm symptoms that are detected depends upon how far the heartworm infestion has progressed.
    - Early infestation: In the beginning stages of a heartworm infestation, no signs are usually detected.
    - Mild infestation: Typically the earliest heartworm sign is a mild, dry cough that is often mistaken by owners for a seasonal cold or allergy.
    - Moderate infestation: As heartworm disease progresses, other signs in addition to coughing include abnormal lung sounds, lack of energy, loss of appetite, weight loss, general discomfort, and fatigue.
    - Severe infestation: In addition to the above signs, more severe symptoms include enlarged liver, pneumonia, swelling around ribcage and/or abdomen, fluid accumulation in the stomach, jaundice, anemia, fainting after physical activity, loss of consciousness, dark bloody urine, and eventual death.

How Long Does It Take Heartworm Disease to Progress?
The seriousness of the disease depends upon a number of factors including the number of heartworms present, the activity level of the dog, and the dog's individual response to the infestation. It takes about 6 months for the heartworm larvae deposited by a mosquito's bite to mature into adult worms, and they then continue to grow. Heartworms may accumulate gradually over years, or quickly when conditions allow exposure to high numbers of mosquitoes carrying infective heartworm larvae. A dog can have heartworm infestation for years without any obvious symptoms manifesting themselves; however, as the heartworms continue to grow, the symptoms will get worse and more obvious.

Overview of Heartworm Disease
How Heartworm Infection is Prevented
How Heartworm Infection is Diagnosed
How Heartworm Infection is Treated

For More Information about heartworms, go to the American Heartworm Society website or The Pet Center.

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