Heartworms and How to Treat Them

Unlike their parasitic cousins (e.g., tapeworms, whipworms, hookworms) that live in the gastrointestinal tract of your dog or cat, heartworms work their way into your pet’s lungs, heart and blood vessels, making them life-threatening. They are introduced into the bloodstream through bites from infected mosquitos, and it takes about six months after your pet is bitten for the larvae to mature into adult heartworms. 

Heartworms can grow up to 12 inches long, and once lodged in one of your pet’s vital organs, they begin reproducing, living anywhere from five to seven years. An infected dog can have several hundred worms in its system. Both dogs and cats can become infected with heartworms.

While worrisome, heartworms are also very preventable. We at Evergreen Animal Clinic recommend you keep your pet on year-round heartworm prevention medication taken orally once each month. 

Symptoms
In the early stages of a heartworm infestation, pets may show few symptoms or no symptoms at all. Over time, more symptoms will likely develop, including:

• Mild, persistent cough
• Decreased appetite, weight loss
• Fatigue, lethargy, exercise intolerance
• Swollen belly from excess fluid
• Difficulty breathing, pale gums, dark-colored urine
• Collapse

Diagnosis 
Blood tests are the first course of action to diagnose heartworms, as well as to monitor pets who are on preventative heartworm medications.

If you pet tests negative, that’s great news! A positive screening test needs to be re-confirmed with another type of test before a definitive positive diagnosis is made. The second test is used to confirm that the first test was truly positive.
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Additional tests may be ordered, including blood chemistry tests, a complete blood cell count, chest x-rays and a urinalysis. An echocardiogram may be used for more severe cases. The results of these tests help determine your pet’s overall prognosis and provide the foundation for a heartworm treatment program.

Treatment & Prognosis
Heartworms are very easy to prevent but are difficult and costly to cure. Treatment tends to be lengthy, expensive and burdensome. There is also the possibility of serious side effects. Once the diagnosis has been confirmed, treatment generally consists of several protocols, including medication, exercise restriction, surgery and/or follow-up testing.  

Medications
If your pet has heartworm disease, multiple medications are used to treat heartworms, both in their juvenile (i.e., microfilariae) and adult stages, as well as to mitigate side effects.

Oral prednisone and doxycycline are often added to the treatment to reduce the chances of a bad reaction to the death of heartworms. Exercise is also restricted during this six- to eight-week timeframe.

Pain medication and anti-nausea medication may also be prescribed because the treatment can cause some discomfort and stomach upset.
The full course of prescription medications should be administered, even if your pet appears to be healthy.

Exercise Restriction
One of the main challenges to eradicating heartworms is keeping your pet’s exercise restricted throughout treatment, which is vital to a successful outcome. This is because physical exertion increases the rate at which the heartworms cause damage in the heart and lungs. The more severe the symptoms, the less activity your dog should have. That means only letting your dog out to urinate or defecate, or to go on very short walks using a leash.

Testing
Tests for both juvenile and adult heartworms are done three to five months (for microfilariae) and six months (for adults) after the last melarsomine injection.

Surgery
In cases where a dog has caval syndrome -- a life-threatening condition in which heartworms located in the heart impede the normal flow of blood leading to cardiovascular collapse -- surgery may be necessary. Under general anesthesia, adult heartworms are physically removed from the right heart and pulmonary artery via the jugular vein. Although worms from the heart are removed, others remain in the pulmonary arteries, so the dog will still require the injection protocol after surgery.

Surgery is risky since the dog’s heart and lung functions are already compromised by the presence of heartworms there. Dogs with caval syndrome may die even with treatment. 

An Ounce of Prevention
Given how challenging heartworm treatment can be, prevention is the best course of action!

If you’d like to get your pet started on heartworm prevention medication, please call us at (805) 937-6341 to schedule an appointment at our Santa Maria, California clinic.