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National Heartworm Awareness Month – April 2019

The American Heartworm Society (established in 1974) celebrates the month of April as the month to raise awareness for one devastating but preventable disease that affects our pets – the heartworm disease.
We are talking about a very serious and potentially fatal condition that is caused by a parasitic worm, a roundworm, that is very long and called Dirofilaria immitis. These worms grow very big and live in the heart, lungs and the associated blood vessels causing severe heart and lung diseases, heart failure, and damage to adjacent organs. Heartworm disease affects also wild animals such as coyotes, foxes, and ferrets that live in close proximity to domestic animals.

Dogs are the natural host for these worms, and the worms that get inside a dog get the possibility to mature to adults. If this condition is left untreated, the number of worms can become several hundred. The worms can seriously damage the heart, lungs and the blood vessels, and even after treatment, there can be serious consequences to the dog’s health.

Cats are not a typical host for the heartworm and that is why most worms do not get to achieve an adult stage in cats. Cats affected with this disease, if they have adult heartworms, it’s only 1 to 3 worms, and most of the time it’s only immature worms. Even though immature, they can cause real and very serious damage. The associated condition in cats is called HARD (heartworm-associated respiratory disease).

The transmission of the disease is by a mosquito. When the mosquito bites an infected animal, in the bloodstream of the infected animal there are baby forms of the parasite, called microfilaria. The mosquito picks up the microfilaria, matures inside of the mosquito for the next 10-14 days into an infective larva, and with the next bite, the matured larva is deposited in the bloodstream of another animal. When the larva gets to the new host, it takes up to 6 months to mature into adult heartworm. Once mature, they can live 5 to 7 years in dogs, and 2 to 3 years in cats. insect 3058526 1920 I Love Veterinary - Blog for Veterinarians, Vet Techs, Students

In the early stages of the disease, there may be no symptoms at all. Signs of heartworm disease may include a mild but persistent cough, unwillingness for physical exercise, lethargy, decreased appetite followed by weight loss. As the disease progresses, pets may have heart failure and swollen abdomen due to the excess fluid from the heart. Dogs that will experience a large number of heartworms, may have “caval syndrome”, a condition of a sudden blockage of blood flow within the heart, which if not surgically treated (to remove the parasites from the heart) can be fatal.

Cats may show very subtle or very dramatic signs. From a mild cough and vomiting to sudden collapse and death.

Test your pet for heartworm disease. If positive, talk to your veterinarian how to proceed with the treatment. Prevention is always the key to a healthy pet. If your pet tested negative, talk to your veterinarian about an effective prevention plan.

Read more about heartworm disease on our blog:

heartworm resistance

heartworm algorithm


  • Note: this article was originally published March 29, 2018.
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