April is Heartworm Awareness Month

By: Jo Singer

What is Heartworm Disease?
Heartworm disease is a serious condition which potentially can be life threatening Heartworm disease is caused by a parasitic worm called Dirofilaria immitis; one of the many species of roundworms. They are called “heartworm” because they live in the arteries of the lungs, heart and the associated blood vessels of dogs, cats and other mammalian species. Cats and dogs of any breed, sex or age are vulnerable to this infection. Heartworm disease in the United States is most common along the Atlantic and Gulf Coasts from the Gulf of Mexico to New Jersey and along the Mississippi River. However, Heartworm disease has been reported in all 50 states.

How is Heartworm Disease Spread?
Heartworm disease is spread by the bite of a mosquito. The dog or cat is called the "definitive" host because the worms mature into adults, mate and produce offspring while they are living inside of the animal. The mosquito is called the "intermediate" host, because the worms live inside a mosquito for only a short period of transition time. The parasitic worm is then spread to the dog or cat by the infected mosquito, which causes heartworm disease.

How long can Heartworms live inside dogs?
The lifespan of the heartworm in a dog is between five to seven years. The adult heartworms resemble cooked spaghetti. Male heartworms generally grow to be around 4-6 inches long, with female heartworms growing between 10-12 inches long. The number of worms living inside an infected dog is called the "worm burden". In dogs, the average worm burden is 15 worms, but it can also range from 1- 250 worms.

What are the Symptoms of Heartworm Disease in Dogs?
There are four classes of Heartworm Disease. The higher the number the worse the disease and the symptoms are more severe.
Class 1: No symptoms or mild symptoms such as an occasional cough
Class 2: Moderate to mild symptoms such as an occasional cough, and tiredness after moderate exercise.
Class 3: A persistent cough, tiredness after mild activity and general loss of body condition. Signs of heart failure are common, and the animal can have trouble breathing. For class 2 and 3 heartworm disease, heart and lung changes are usually seen on chest x-rays.
Class 4: Is also called caval syndrome. There is such a heavy worm burden that blood flowing back to the heart is physically blocked by a large mass of worms. Caval syndrome is life-threatening and quick surgical removal of the heartworms is the only treatment option. Unfortunately, even with surgery, this stage is generally fatal.

How are dogs tested for Heartworm?
Blood tests are the most common method used for checking out dogs and cats for heartworm.

When should dogs be tested for Heartworm?
Before starting heartworm prevention, dogs older than six to seven months old should be tested before starting heartworm prevention. Even if a dog appears to be healthy, if a heartworm-positive dog is not tested prior to starting heartworm prevention, the dog will remain infected with heartworm until it is sick enough to display symptoms.

Is there treatment available for Heartworm Disease in Dogs?
Depending on the dog’s stage of infection, there are FDA approved drugs for treating dogs infected with adult heartworms. But prevention is the best treatment for heartworm in dogs. There are many FDA heartworm prevention medications available today which all need a prescription from a veterinarian. Your veterinarian will be able to recommend the most appropriate prevention method for your dog.

Cats can also get Heartworm Disease.
Although cats are not as susceptible to heartworms as dogs, if cats are bitten by an infected mosquito cats can also get Heartworm disease. Because the worms don’t thrive as well in the cat’s body they are considered “resistant” hosts. Both indoor-only and outdoor cats are at risk of Heartworm disease.

Heartworm infections are more difficult to detect in cats than dogs. Two types of blood tests in combination are used to check for heartworm in cats. Negative tests however do not rule out heartworm infection, and positive tests may not indicate that an active infection exists. In addition to blood test results, ultrasound of the heart and x-rays are often used to determine if a cat has heartworm disease.

Not all cats show symptoms of heartworm disease. Some cats never show any symptoms at all and can rid themselves of heartworms. However some cats that are infected can die suddenly without ever showing any signs of being ill. Many of the symptoms of heartworm disease in cats are non-specific and can mimic other illnesses, such as weight loss, lethargy, decreased appetite, and vomiting. Rarely do cats with heartworm disease show signs of heart failure. Cats with heartworm disease may show symptoms of upper respiratory illness due to the damage to the lungs caused by the heartworms.

There is no FDA approved treatment for heartworm in cats but symptoms can be managed medically.

There are several FDA approved drugs for Heartworm prevention in cats. Once again, the best treatment for heartworm disease is prevention. Before prevention is begun it is recommended that cats be tested for active heartworm infection. Talk with your veterinarian about having your cat tested for heartworm.

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