What to Know About Heartworm


During the summer is the time where everyone is outside enjoying the nice warm weather, whether it’s just in the back yard or going out hiking or camping. It’s not just you and your pets though that are enjoying the lovely weather, all the bugs are too. Cats and dogs are prone to catching lots of different kinds of parasites especially during the summer. One of the parasites that your pet can catch during the summer is heartworm also known as Dirofilaria immitis.

Heartworm is a very serious and also potentially fatal disease. It is a foot-long worm that lives in the heart, lungs and even the blood vessels. In some cases there can be ten to hundreds of worms in the body. The main location that they go to is the heart. They can last 6-8 months in your pet’s body. The stage at which they can be diagnosed is when they are microfilaria. This type of parasite can cause heart failure, lung disease and even damage other organs within the body. The way that your pet can get heartworm is through the transmission of an infected mosquito when they bite your pet. Heartworm affects dogs, cats and ferrets.

Dogs are the natural host for heartworm. The worms will live inside the host where they will mature into adults, mate and reproduce offspring. If left untreated the numbers can increase to over hundreds of worms within the body causing lasting damage to the heart, lungs and arteries and also reducing the quality of life in your pet. Dogs should be tested annually to check for heartworm disease and to see if the prevention program that they are on is working. Puppies under seven months can start on the preventative without getting tested as it takes six months for the worm to become an adult. After six months of age they should get tested to make sure they don’t have heartworm disease. Adult dogs may need to be tested for adult heartworm prior to being put on a preventative treatment program. Some clinical signs that you could see are lethargy, exercise intolerance, signs referable to right-sided cardiac enlargement. There are two tests that can be done for dogs, the Modified Knott’s (Millipore filtration) and ELISA antigen test. The one that we use here at our clinic is the ELISA antigen test. For preventatives there are a few different kinds that are out there for dogs. The ones that we carry here at our clinic are Heartgard (a chewable tablet that you give to your dog orally) and Advantage multi (topical liquid that you place on the skin in between the shoulder blades).

In cats they are different then to the dog when it comes to heartworm. Cats are an atypical host, making it hard for the parasite to survive. Most heartworm don’t make it to the adult stage. Unlike for dogs where they can get up to hundreds of worm’s cats only get one to three. Even if the worms are immature they can still cause real damage to the body. A condition that can form is heartworm associated respiratory disease (HARD). Since heartworm is such a rare thing to see in cats it often goes undiagnosed. Some acute (sudden) clinical signs that you could see are diarrhea/vomiting, increased breathing, sudden death. Chronic signs that you could see are coughing, vomiting, weight loss, anorexia, dyspnea and lethargy. The way that your cat can catch heartworm is when they are bitten by an infected mosquito, same as the dog. A preventative that you can use that we carry here at our clinic is Advantage multi (topical liquid that you put on the skin in between the shoulder blades). Your cat should be tested before being put on a preventative, the test that is done for cats is the ELISA antibody or antigen test. For the antibody test it detects exposure to heartworm larvae. Once being on the Advantage multi you should retest your cat just like you would for the dog to make sure it is working.

Remember to still have fun this summer and enjoy all the adventure’s that you can go on with your pets. Just like you keep yourself protected from bugs remember to do the same for your pets.

Written by Christy Yakimetz, AHT, ACA,