WHAT ARE HEARTWORMS?

Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living the the arteries of the lungs and in the right side of the heart of dogs, cats, and other species of mammals, including wolves, foxes, ferrets, sea lions, horses, and humans. Heartworms are classified as nematodes (roundworms) and are but one of the many species of roundworms. The specific roundworm causing heartworm in dogs and cats is known as Dirofilaria imminitis.

Dogs or other animals harboring adult worms are the recognized reservoir of infection. Adult worms produce the offspring that circulate in the blood and are then transmitted to mosquitoes once they bite the infected animal. These offspring (microfilariae) undergo development to an infective larval stage within 14 days in the mosquito, and can then be transmitted to another host (such as a cat) or back to another dog, when the infected mosquito bites again. The infective heartworm larvae travel through a tubular organ within the mosquito's head and are injected into the skin of a new host animal through the mosquito bite wound. In the dog, the larvae progress in their development to an adult form of the worm, and live in the heart and pulmonary vessels, where they continue the life cycle and cause extensive injury. In the cat, the larvae molt as well, but fewer worms survive to adulthood. While dogs suffer severe heart and lung damage from heartworm infection, cats typically exhibit minimal changes in the heart. The cat's primary response to the presence of heartworms occurs in the lungs.

Within the dog, the time frame between initial infection and growth to adult worms is approximately six to seven months, eventually arriving in the heart and pulmonary vessels where they begin to produce new offspring.

In cats, it takes seven to eight months before adult worms arrive in the heart and pulmonary vessels. In most cases the life cycle of the heartworm ends here since microfilaria are produced in less than 20% of cats.

Some worms may get up to 3 feet long. Heavy infestation of heartworms will cause swelling in the lungs, pulmonary arteries, kidney and heart, which will eventually cause the animal to die. Heartworm infestation can also cause anemia and liver damage.

WHAT ARE THE SYMPTOMS OF HEARTWORM?

Symptoms of heartworm may include loss of appetite, lethargy, exercise intolerance, weight loss, fever, dyspnea (difficult, labored breathing, shortness of breath), coughing, weakness, dull dry coat, and hemorrhage.