Take This (Heartworm Testing) Advice to Heart

August 26, 2020 | 12:58 PM

At your dog’s yearly examination, you and your vet will likely discuss heartworm testing. Even if your dog is already on year-round heartworm prevention, annual heartworm testing is important. Luckily, the test is easy, and there are many types of preventatives that can protect your pet from becoming infected.

Heartworms are parasites spread by mosquitoes. They live in the heart, lungs, and blood vessels, and can cause severe lung damage, heart failure, and even death. Clinical signs of heartworm disease include cough, exercise intolerance, and lethargy. All dogs, even indoor-only dogs, are susceptible. Less commonly, cats may also be affected. It only takes a single mosquito bite in an unprotected pet for infection. Although heartworms used to be rare in many parts of the United States, weather changes and increased pet travel have increased the distribution of cases nationwide (especially Philadelphia).

Whether your dog is starting his first dose of heartworm prevention, or has been taking it for years, annual testing is one of the most important parts of your visit. For dogs just starting heartworm prevention, it is important to first rule out an existing heartworm infection. If your pet is already heartworm positive, preventative medication can actually have harmful side-effects, and your veterinarian will need to start heartworm treatment first. It is important to quickly identify heartworm positive animals so that treatment can be started immediately. Make sure to let your veterinarian know if your pet is not currently on any preventatives, or if you have missed any doses. It takes several months for heartworms to develop, so your veterinarian will help you determine the best time to test your pet. 

In order to check for heartworms, your veterinarian will take a small blood sample and will run a test commonly called a “SNAP” test. This test can be run by your veterinarian, or at an outside lab. If completed by your veterinarian, results are usually available in less than 10 minutes. Some vets may use a test that also screens for Lyme disease and two other tick-borne diseases (Anaplasma and Ehrlichia). Testing is also available for cats, although it is more difficult to determine if cats are truly infected with heartworms. For cats, the SNAP test usually also includes two viral diseases commonly referred to as FIV and FeLV (feline immunodeficiency virus and feline leukemia virus). Unfortunately, a fecal sample can’t be used to test for heartworms.

Once your veterinarian determines that your dog is heartworm-free, it will be time to select your preferred type of heartworm prevention. 

There are several different types of heartworm prevention available! The most common types are oral tablets, given every month. Some topical formulations are available as drops that you apply to your dog’s skin. Some vets also offer injectable heartworm prevention that lasts for a longer period of time. For cats, the most common preventatives are topical, though oral tablets are occasionally available as well. Your veterinarian may recommend certain products for your pets based on cost, other benefits (such as flea or intestinal parasite prevention), or availability. For dogs, a heartworm test is required prior to dispensing these medications, and you can only buy these medications through a veterinarian. Your veterinarian will require a recent negative heartworm test on file to fill these medications for your dog.

If your pet develops heartworms, it is important to begin treatment as soon as possible to prevent further damage from the parasite. Unfortunately, appropriate heartworm treatment is expensive and time consuming. Although the heartworm treatment protocol is tailored to the individual pet, appropriate treatment is usually a several month process. In fact, it may take up to a year for your pet to be cleared of the parasite. Once diagnosed as heartworm positive, your vet may recommend confirmatory testing, or other tests, such as X-rays, to determine the extent of your dog’s infection. Then, a series of oral and injectable medications will be started to kill the heartworms. During the process, you will need to restrict your pet’s physical activity to reduce the risk of possible side effects of treatment. The most dangerous risk of heartworm treatment is the formation of a blood clot within the lungs (pulmonary thromboembolism), which can be life-threatening.  

Heartworm infection carries a significant risk to your pet and heartworm treatment is lengthy and expensive. Thankfully, heartworm testing is quick and prevention is readily available through your veterinarian. At your next visit, be sure that your dog has an up to date heartworm test and discuss with the doctor or veterinary staff how to choose an appropriate preventative for your pet.