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There were over 150,000 new cases of heartworms in the United States in 2003.

The map shows concentrations of heartworm disease to be heaviest in the southern regions and warmer climates. 

What causes heartworms?

Mosquitoes transmit heartworms. Therefore, heartworm disease is more prevalent in areas that are warm and humid. In the southeast United States heartworms are virtually a year-round problem.

Mosquitoes harbor microscopic baby heartworms in their blood and saliva. When an affected mosquito bites a dog, baby heartworms burrow under the dog’s skin and travel to the lungs and heart over a period of 6 months. These baby heartworms then grow to an adult size of 4 to 9 inches. Dogs always get heartworms from mosquitoes. One dog cannot give another dog heartworms.

What damage do heartworms cause?

Adult heartworms living in the heart and lungs can cause severe damage to the tissues in these organs. This can lead to heart and lung disease. Symptoms of affected dogs often include coughing, breathing difficulty, excessive panting, sudden collapse and even sudden death. Severe heartworm infestation can also damage other organs such as the liver and kidneys.

How is heartworm disease diagnosed?

A simple 10 minute blood test is the most commonly used method for diagnosing heartworm disease. Heartworm preventatives are extremely effective with protection being about 99%. However, no heartworm preventative is 100% effective, and sometimes a month or more of medication is not given. For these reasons we test all patients once a year. Annual heartworm testing allows us to catch many infections before they become severe, thus increasing the safety and effectiveness of heartworm treatment.

Other tests used prior to heartworm treatment include a microfilaria test, which detects the presence of baby heartworms in the blood. Chest x-rays help determine how severely the heart and lungs are effected, bloodwork gives information about the liver and kidneys, and echocardiogram (ultrasound of the heart) helps detect abnormalities inside the heart. Each of these tests play a role in determining how severe the patient’s heartworm infection is, and allows your veterinarian to determine the safest possible way for treating your dog.

How is heartworm disease treated?

Heartworm disease is very treatable. Injections are given to kill adult worms, and liquid medication is given to kill the microfilaria (baby heartworms). There are risks associated with heartworm treatment. In most cases, patients are cured, return to normal, and can be started again on heartworm preventative. Some patients, often those with severe cases, have severe reactions to the treatment, which require hospitalization and additional care. Occasionally these reactions are so severe that the patient dies. We do everything we can to make the pre-treatment diagnostics as thorough as possible, and make the treatment as safe as possible. If you have any questions about heartworm disease and your dog let us know.

Heartworms in Cats

Although heartworms occur commonly in dogs, most people do not consider them a problem for the cat. However, recent studies of cats with heart and respiratory diseases have found an incidence of heartworms that is far greater than we previously thought. Even if your cat stays indoors, it is still at risk for heartworm disease. All it takes is one infected mosquito, and we all know there have been times when there have been mosquitoes in the house.

Heartworm disease in cats is transmitted the same way as in dogs. The difference is there is currently no drug approved for treating this disease in cats. There are several methods for diagnosing heartworms in cats. Unfortunately, none are 100% reliable so a combination of tests is often needed. There are two relatively new tests that are proving to be very helpful in diagnosing heartworms. The heartworm antibody test determines the cat's immune system has been exposed to heartworms. A positive test may indicate that an active infection is present. However, cats who have had heartworms but whose heartworms have died will also have antibodies for an unknown period of time; suspected to be 2-4 months. Cats with late stage larvae that are not yet adults and cats with adult heartworms in places other than the heart may also test positive with the antibody test. This test is very sensitive, so it is used first. However, if it is positive the next test is performed. The next test is the heartworm antigen test. This detects the presence of adult female heartworms. It is very specific, but not as sensitive. A positive test indicates that heartworms are present, but a negative test does not mean they are absent. In summary, a diagnosis of heartworms is confirmed if both the antibody and antigen tests are positive. The next set of test follows the same protocol as in dogs with the use of ultrasound and xrays.

The best way to insure that your cat stays free of heartworms is to keep her on monthly heartworm preventative available and guaranteed at your veterinarian's office.

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