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Heartworm Disease in Dogs and Cats

Posted 2020-06-22


April is heartworm awareness month, which means it’s that time of year when your veterinarian may want to check your dog or cat for heartworm disease.

Heartworm in pets is a serious and potentially fatal disease that is caused by foot long worms (heartworms) that live in the heart, lungs, and associated blood vessels of affected dogs and cats. The heartworm can cause severe lung disease, heart failure, and damage to other organs in the body. It affects dogs, cats, and other mammals such as wolves, coyotes, foxes, sea lions, and in rare instances humans.  Thankfully, in my practice, I only see a few cases of heartworm in dogs a year. Although, even in those few instances, the conversation with the animal’s guardian is always difficult as the treatment is hard on my patients, and can be costly.

Like most pathogenic infections, the earlier a diagnosis can be made the better chance for recovery. Be sure to have your dog or cat checked this spring for heartworm disease.

How is Heartworm disease in pets transmitted?

Heartworms are transmitted through the bite of a mosquito, which carries immature larvae from the parasite Dirofilaria immitis. These larvae enter into the pet’s skin through the mosquito bite. From the site of the mosquito bite, the larvae molt and travel through the pet’s body, until they enter the pet’s heart and pulmonary vessels in the lungs. Once in the pulmonary vessels they grow, pushing up until some reach the pulmonary artery.

The now mature heartworm reproduces, creating microfillaria, which circulate in the blood stream of the pet. When a mosquito bites the infected pet and takes a blood meal, it picks up the microfillaria. When this mosquito then bites another pet, it transmits the infection.

Once mature, the heartworm can live up to 5-7 years in dogs, and 2-3 years in cats. Since the heartworm can live so long, this can lead to an increasing number of worms in an animal as a pet becomes infected over and over each mosquito season.

How is Heartworm in pets diagnosed 

Heartworm infection in both cats and dogs is diagnosed by a blood test. If the test is positive, other tests will be ordered to diagnose the stage of the heartworm disease. Heartworm testing should begin at 7 months in a puppy, and annually in adult pets if protected with prevention.

What are the signs and symptoms of Heartworms in pets?

Unfortunately, there are little clinical signs in the early stages of the disease, which is why testing is so important. As the disease advances, dogs may exhibit a cough, decreased interest in exercise, fatigue after moderate activity, decreased appetite, and weight loss. As the disease further progresses, signs of heart failure ensue, including worsening respiratory signs and cough, swollen belly and in worst cases “caval syndrome”, which is a form of cardiovascular collapse.

With cats, the signs of heartworm can be extremely subtle or very sever. Symptoms may include coughing, asthma like attacks, vomiting, lack of appetite, and weight loss. Unfortunately, the first sign of heartworm disease in some cats is sudden collapse or even death.


Heartworm disease has been diagnosed in 50 states. Protecting your pet with good nutrition and a healthy lifestyle that includes heartworm prevention is the best thing you can do.

Natural supplements, such as NHV Hearty Heart and natural parasite cleansers like NHV Inulin PK may help with heartworm disease.

For extra support, I would also recommend NHV Stimmune, as well as NHV Milk Thistle, and the superherb NHV Turmeric, which will help support your pet’s body.

Natural mosquito repellents are also recommended.

For further information please feel free to leave a comment below or contact me for an on-line consultation.

Dr. Hillary Cook is a graduate of Virginia Maryland Regional Veterinary Medical school. She has been practicing holistic and integrative veterinary medicine for fifteen years. She certified in Veterinary acupuncture and is fully qualified in Western and Chinese herbalism. She is the owner of Animal Wellness Center, an integrative veterinary clinic in Crozet, VA. She enjoys spending time with her husband, two children, and a menagerie of pets including dogs, cats and chickens. When time allows, you can find her in the garden or on the tennis court!

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