Heartworm Disease

<>Heartworm disease is a preventable, but serious and potentially fatal, parasitic disease that primarily affects dogs, cats and ferrets. It can also infect wild animals, such as exotic canids. There are documented human infections, but they are thought to be rare and do not result in clinical disease.

Heartworms are transmitted from animal to animal by mosquitoes. When a mosquito bites an infected animal, young heartworms called microfilariae enter into that mosquito's system. Within two weeks, the microfilariae develop into infective larvae which are then injected into another animal through the mosquito's bite. Over the next six months, the infected larvae mature into adults: during the first three months, the larvae migrate through the animal's body eventually reaching the blood vessels of the lungs; during the last three months, the larvae become adults and enter the heart.  Once in the heart, the heartworms will continue to grow up to 14 inches in length. In time, the worms will injure the blood vessels, resulting in severe lung and heart disease. If worms of both sexes are present, they will create new microfilariae that can damage other organs when the animal's immune system attempts to combat the infection. This life cycle continues when a mosquito bites the infected animal and ingests the microfilariae.  Heartworms may survive for 5 to 7 years in dogs and 2 to 5 years in cats.

This information has been prepared as a service by the American Veterinary Medical Association.

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