Heartworm disease is a serious and potentially fatal disease in dogs, and to a lesser degree, in cats. Heartworms, which look like strands of thin spaghetti, grow in the heart and adjacent large blood vessels. They clog the heart and arteries, interfering with the valve action of the heart and reducing the blood supply to other organs, particularly the lungs, liver and kidneys, reducing their ability to function properly. Left untreated, the heartworms will further reduce the flow of blood and oxygen to the major organs, causing damage to them that limits their ability to do their jobs. Toxins that could not be filtered out build up in the dog’s body and eventually it dies of congestive heart failure.

Heartworms are transmitted from one dog to another by mosquitoes. A female heartworm produces millions of offspring called microfilaria. They float around in the dogs blood and can cause some problems by clogging tiny blood vessels, but they cannot grow to be adult heartworms in the body of the dog in which they were born. When a mosquito bites an infected dog, it takes in blood containing microfilaria. These organisms remain in the mosquito for 10-30 days, during which time they change into what are called infective larvae. When the mosquito bites a new dog, these infective larvae enter the dogs bloodstream and travel to the heart, where they grow to maturity in 2-3 months and begin to reproduce, completing the cycle.

That was a nutshell version; there is a lot more to the heartworm problem than these two paragraphs, but the fact is that there doesn’t have to be a problem. Heartworm disease is preventable and has been for years. A number of pharmaceutical companies offer preventatives in the form of tasty chewable tablets that are given once a month. For those who cannot remember to give the dog a tablet when it is due, there is a preventative that is injected and gives six months of protection. Most vets will even remind you when the next shot is due.

In northern states, where it gets cold in the winter and stays that way, many people stop giving heartworm preventative in the fall and start again in the spring. Farther south in warmer climes, mosquitoes are a problem all year, and preventative must be given continually. Metro Atlanta is sort of on the cusp, and it was thought that it was safe to discontinue giving the preventative during the winter. Recent research suggests that winters here are not cold enough for long enough to kill all of the mosquitoes, and that it is necessary to continue treatment all year.