As I sat on my back porch, watching my dogs play, I looked down and saw a mosquito preparing to snack on my ankle. A quick slap ended her quest to suck my blood, but the incident served as a reminder that it’s mosquito season again. That means it’s critical that your dog be protected against heartworms.

Heartworm disease is a serious and often fatal condition caused when parasitic worms live in the heart, lungs and associated blood vessels of dogs. Mosquitoes spread the disease when they bite an infected dog and themselves become infected with microfilariae. The microfilariae mature inside the mosquito, and the mosquito bites another dog, the larvae migrate into the new host. In six to seven months, these larvae will mature into adult worms and lodge in the heart, lungs and surrounding blood vessels and begin reproducing. The lifecycle continues and the number of worms builds up within the infected animal. Adult worms can grow up to 12 inches in length and can live five to seven years.

Heartworms may accumulate gradually, or quickly if the dog is exposed to a high number of infected mosquitoes. Recently infected dogs, or those with a low number of heartworms, may not exhibit outward signs of the disease. As the heartworm burden increases, however, symptoms begin to appear.

Because heartworms live in pulmonary arteries and later in the lungs, the dog may cough and experience shortness of breath. He may appear listless or have less endurance, and as the disease worsens, most dogs will avoid exercise. As the heartworms grow, they will crowd the heart chambers. This slows down blood flow and decreases the oxygen supply to the dog’s body. Dogs may experience loss of consciousness due to poor blood flow to the brain. The stress on the dog’s vital organs can indirectly affect other organs, like the kidneys, and can cause irreversible damage. Finally, dogs may die suddenly due to heart failure, blood clots, bleeding in the lungs or cardiovascular collapse.

How bad is the heartworm problem? The answer varies by state, but in Alabama the problem is very severe. According to the American Heartworm Society, in 2010, reporting veterinary clinics throughout the state saw a minimum of six to 25 cases per clinic, while other areas saw 26-50 cases per clinic. In much of Lee and Russell counties, including Opelika and Auburn, the instance was 51-99 cases per clinic. In a few areas of the state, reporting clinics saw over 100 cases.

If your dog has heartworms, they will kill him unless you treat them. Treatment consists of one to three injections of Immiticide, an arsenic-based product. The injection is given in the muscles near the spine, and is very painful for the dog. After the injection, the worms begin to die. Dogs must be crate-rested and kept as quiet as possible for at least a month following treatment, in hopes of preventing large clots of dead worms from breaking up and passing through the lungs. Sometimes, despite limited exercise, this will occur anyway. One of my foster moms came home and found the rescued lab she was fostering for me dead in her crate for this very reason. Treatment is also expensive. Because it involves laboratory testing, X-rays, hospital stays and expensive medication; you can spend a lot of money treating your heartworm positive dog.

The good thing is, your dog does not have to get heartworms.

There are a variety of options for preventing heartworm infection, including daily and monthly tablets and chewable pills, as well as monthly topical treatments. Some of these products are combined with other medications that will kill other types of worms and/or stop fleas. The products are only available through your veterinarian or with a prescription. Your vet will insist on heartworm testing your dog prior to beginning a course of preventative, and yearly after that, as it is dangerous to give preventative to an infected dog. Puppies should be started on preventative at about eight weeks of age, and as long as they’re less than six months of age do not require a screening test. The American Heartworm Association recommends dogs be kept on preventative year round.

A heartworm positive diagnosis does not have to be a death sentence for your dog. Appropriate treatment can save your dog’s life. Far better than treating an infected dog, though, is taking the steps necessary to prevent your dog from getting heartworms in the first place!


Karlene Turkington, a Certified Professional Dog Trainer, is a lifelong animal lover who has been training dogs for over 20 years. Readers are welcome to send their questions to: Information provided here is a basic overview of issues. Specific health or behavioral concerns should be discussed with your veterinarian or qualified animal trainer or behaviorist.