Just as the name suggests, heartworms are parasites that live in the heart and large vessels between the heart and lungs of dogs and cats. The worms become very large and cause damage to the heart and vessels. Over time, this infection, if not treated, can lead to congestive heart failure and death.
Heartworm larvae develop inside carrier mosquitoes. When an infected mosquito bites a dog or cat, the worm larvae enter its bloodstream. The larvae travel to the large vessels at the heart and develop into adults. If both male and female heartworms are present they will mate and release eggs into the animal’s blood. Another mosquito bites the animal and ingests the heartworm eggs. The eggs develop into larvae inside of the mosquito, and the entire cycle starts again.
Fortunately, we can prevent heartworms from developing in our dogs and cats! Consistent administration of approved medications kills heartworm larvae if the animal is bitten by an infected mosquito. These medications are available as monthly flavored pills, monthly topicals, or 6 or 12-month injectables. We strongly recommend starting your pet on heartworm prevention as puppies and kittens and keeping them on it year-round. Even indoor pets should be on heartworm prevention because mosquitoes can get inside your house (I have been bitten more than once while indoors!).