Dear Dr. Barchas,

What is heartworm? Does my dog need to take medicine for it? Can cats catch it, too?

Elizabeth, Washington, DC

Heartworm is a blood parasite of dogs and cats. It is spread by mosquitoes. After a pet is infected, worms develop that live in the heart and the arteries leading out of the heart. Severe infections can cause heart failure and death.

Fortunately, several medications exist that prevent heartworm disease. These medications are highly effective and extremely safe, and are available for both dogs and cats. Most are given on a monthly basis. Many heartworm preventatives also help to remove certain intestinal parasites from pets as well. Blood testing for heartworm disease may be necessary before starting a preventative program.

Heartworm disease occurs throughout much of the world, including most of the United States. However, each pet’s risk varies with season, location, and lifestyle. In general, pets living in warmer areas are at greater risk than those in colder climates.

I strongly recommend that you discuss your pet’s circumstances with your veterinarian to determine whether heartworm testing and prevention are appropriate.