Heartworm is a blood parasite in dogs, and has recently been recognized in cats as well.  The parasite is transmitted by mosquitoes.  A mosquito bites a heartworm infected dog, then bites another dog, transmitting the parasite.  The parasite flows through the blood and develops over time into a 6-12 inch worm in the pulmonary artery, right outside the heart.  While heartworm is treatable, the treatment is expensive and not without risk.  Heartworm is eventually fatal if not treated.  Prevention is very safe, effective, and labeled for lifetime use.   The preventative also can treat a number of intestinal parasites as well, depending on the brand of heartworm preventative.

Heartworm has been diagnosed in all 50 states.  Number of cases is unfortunately high, despite the ease of treatment (a once a month chewable tablet).  Cases diagnosed in Washington state are increasing, though it is much more common in warmer climates, such as the South.

Your dog can be tested for heartworm with a simple blood test, then started on a preventative (a once-a-month chewable tablet).  Cats are not the natural host, but parasitologists have recently discovered that cats can be infected (usually by 1-2 worms) which causes asthma-like symptoms.  Cats going outside should be on a heartworm preventative, which is a once-a-month topical medication.

Please visit the American Heartworm Society (www.heartwormsociety.org) for more information.