Heartworm Disease

Heartworm disease is a potentially fatal condition of parasitic worms living in the arteries of an animal’s lungs or the right side of its heart. Heartworm disease has been reported in all 50 states. It is particularly endemic in the southern regions of the United States.

How it Begins

An adult female heartworm releases her offspring, or microfilariae, into the bloodstream of an infected animal. When a mosquito bites the infected animal, the microfilariae enter the mosquito. The larval stage of the heartworm is achieved while inside the mosquito. When the mosquito bites another animal, the larvae are transferred to the animal. The larval stage lasts just over six months. Adult heartworms can live within an animal for up to 7 years.


Dogs can be infected with heartworms for years before exhibiting any symptoms. Heavily infected dogs may show clinical signs including, persistent cough, reluctance to move or exercise, fatigue and weight loss.

Cats are not as often infected in the U.S. Symptoms of heartworm disease in cats are similar to many other feline diseases and include rapid breathing, difficulty breathing, vomiting, weight loss and lethargy.


A simple blood test can detect an adult female heartworm’s antigen. Other tests can detect microfilariae. Heartworms can also be detected upon ultrasound or radiograph of an infected animal’s heart and lungs.


Treatment of Heartworm Disease in dogs is dangerous and costly and can take weeks of treatment to be effective. There is no effective treatment for heartworm disease in cats.

Heartworm prevention is safe, easy and inexpensive. Our Veterinarians recommend a monthly oral preventative called Tri-Heart Plus. This chewable treat disrupts the lifecycle of the heartworm, preventing it from ever reaching its adult form.  It also includes a de-wormer to keep your pet free from hookworm and roundworm.

Our veterinarians recommend year-round lifelong heartworm prevention. At the very least, your dog should be on a heartworm preventative during the danger months of May through October. A heartworm test is recommended prior to using a preventative in animals that are older than six months and those that are not on a year-round preventative program.

 Zoonotic Disease

Certain intestinal parasites like hookworm and roundworm are zoonotic diseases, diseases that can be passed from pet to human. People at risk for zoonotic diseases include individuals with weakened or undeveloped immune systems. This includes very young children, pregnant women, those with certain medical problems, the elderly, and animal healthcare workers. It is our responsibility to our clients to discuss zoonotic diseases. We recommend a monthly heartworm preventative for dogs to prevent the spread of disease to your family. For cats, we recommend regular treatment with a wide-spectrum de-wormer.


—Janni Kimble, RiverWoods Pet Hospital

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