Our last 2 blog posts discussed heartworm disease and prevention. This blog post is the 3rd and last in the series that will discuss diagnosing and treating heartworm disease in both dogs and cats. We always hope not to get to this point, but for pets not reliably on preventative or maybe newly adopted with pre-existing disease, we sometimes find it necessary to try to diagnose and treat an existing infection.

Treating dogs with heartworm disease is more straightforward, although it can still be quite involved, expensive and risky. If a dog tests positive for heartworm disease, a 2nd heartworm test is done, often through a different lab than the 1st test to help rule out a false positive. A heartworm microfilaria test is also run to check for immature heartworms in the bloodstream. There is not a test that will tell us how many mature heartworms your dog has, so all cases are treated as if they have a higher worm burden.

Other tests will be needed and may include a chemistry panel and CBC, urinalysis and chest radiographs. In some cases echocardiogram may also be recommended. Diagnostic tests needed and treatments given may vary depending on your dog’s age, health status and other factors.

Before, during and after treatment, exercise restriction is very important. Treatment involves killing adult heartworms in the heart, lungs, and/or arteries. Keeping your dog as low key as possible while this is happening will help to prevent serious reactions caused by dying worms. Antibiotics and steroids may also be given to help reduce the chance of a reaction. It is very important to follow all directions and restrictions as closely as possible. Monthly heartworm preventatives will also be given during the treatment period.

The accepted treatment for heartworm disease is a series of 3 injections (over a 30 day period) with the drug Melarsomine (Immiticide). These injections are given via a deep intramuscular injection in the lumbar muscle (spine region). Because these injections can be painful, pain medications are typically given. Dogs must be observed closely after each injection and exercise must be greatly restricted to help avoid reactions to the death of adult heartworms. Consistent exercise restriction is typically needed for an additional 6-8 weeks after the last Meslarsomine injection has been given.

3-5 months after treatment, the dog should have a blood test to look for microfilaria in the bloodstream. At about 6 months out a heartworm antigen and another microfilaria test are recommended to make sure treatment was successful. After that, monthly, year round heartworm preventatives should be administered.

As we talked about in the first blog post in this series, heartworm diagnosis and treatments in cats is much more difficult and frustrating to deal with. The only way to definitively diagnose heartworm disease in cats is through necropsy. If cats are exhibiting possible heartworm symptoms and other disease processes have been ruled out, multiple and repeated diagnostic tests are often needed. Antigen tests can have a high incidence of false negatives in cats, so repeated positive tests along with positive antibody tests are more indicative of a heartworm diagnosis in cats. Thoracic radiographs that show enlarged pulmonary arteries can be supportive of this diagnosis along with physical symptoms.

Treating heartworm disease in cats is equally difficult. There is not an approved medication to treat feline heartworm and many times the best option is to try to treat the symptoms until the worms die off on their own (typically 2-3 years in cats versus 5-7 years in dogs). If cats are having severe symptoms they may need oxygen treatment, steroids and possibly medications to remove fluid buildup in the lungs. The threat of sudden collapse and death is always present. In severe cases of feline heartworm disease, surgery to remove the adult by a specialist may be an option, but the risk is high and up to 40% of cats who undergo this procedure do not survive. This option is typically used as a last resort in cats with a very poor prognosis without surgery.

In both dogs and cats prevention of heartworm disease is so much easier, safer and less expensive than trying to diagnose and treat existing infections. Heartworm preventatives are very safe and generally easy to give. Don’t take the chance of your pet getting heartworm disease. Talk to your veterinarian about prevention to decide which option makes the most sense for you and your pet.