What is heartworm disease?
Heartworm disease is a preventable, but serious and potentially fatal, parasite that primarily infects dogs, cats and ferrets. It can also infect a variety of wild animals including foxes, wolves, coyotes, tigers, lions, pumas, raccoons, opossums, sea lions, seals and others.
What causes heartworm disease?
Heartworm disease is caused by a parasite called “Dirofilaria immitis.” Heartworms can only be transmitted from animal to animal by mosquitoes. When a mosquito bites an infected animal, young heartworms called microfilariae enter into that mosquito’s system. Within two weeks, the microfilariae develop into infective larvae inside the mosquito; these larvae can then be transmitted to another animal by the mosquito.
The infective larvae mature into adult heartworms in approximately six months. During the first three months, the larvae migrate through the animal’s body, eventually reaching the blood vessels of the lungs. During the last three months, the immature worms continue to develop and grow to adults, with females growing to lengths of up to 14 inches. The worms damage the blood vessels, and reduce the heart’s pumping ability, resulting in severe lung and heart disease. Adult heartworms can survive for 5 to 7 years in dogs and several months to years in cats.
You can never fully comprehend the devastating impact this disease can have on a dog or cat. To view a video of live heartworms in a dog that has died, please visit this link. WARNING: GRAPHIC VIDEO. The emphasis in this graphic video is the devastation of heartworm disease. Visit www.heartwormsociety.org for more information. Video complements of: Copyright Merial ltd. Duluth, Ga. Used with permission.
Where are heartworms found?
Geographically, heartworms are a potential threat in every state as well as in many other countries around the world. All dogs, regardless of age, sex or living environment, are susceptible to heartworm infection. Indoor, as well as outdoor, cats are also at risk for the disease.
How can my pet be tested?
Antigen: These are commonly referred to as “snap” tests. These are the tests most commonly used by veterinarians in detecting the presence of heartworm infection. They detect specific antigens primarily found in female heartworms and are used with much success to detect canine heartworm infection. Most commercial tests will accurately detect infections with one or more mature female heartworms that are at least seven or eight months old, but the tests generally do not detect infections of less than five months duration. (These tests will fail to detect infections of immature heartworms, infections with only male heartworms and some infections with only one adult female worm, however they are the best available in detecting the presence of infection.) It is recommended and important that your pet be tested for heartworms at least once per year.
Microfilarial Detection: The identification of the offspring (microfilariae) of heartworms (Dirofilaria immitis) from a blood sample indicates infection with adult heartworms. Veterinarians will sometimes do a quick examination under a microscope of a blood smear to look for the presence of the offspring (microfilariae), but this procedure is not sensitive enough to rule out heartworms and only verifies the presence of an infection. Microfilariae are not present in single sex infections. If adult worms of both sexes are present, they will mate and produce new microfilariae. It is recommended and important that your pet be tested for heartworms at least once per year.
Radiology (X-Ray): Radiographic abnormalities develop early in the course of the disease. X-rays of the heart and lungs are the best tools available to evaluate the severity of the disease and to develop a prognosis. Typical changes observed are enlargement of the following structures: pulmonary arteries in the lobes (particularly the lower lobes) of the lung, main pulmonary artery, and right side of the heart. Blunting and thickening, usually along with tortuosity (abnormal twists or turns), of pulmonary arteries, is often noted. Inflammation is often found in the lung tissue, particularly the tissue that surrounds the pulmonary arteries.
When should my pet be tested?
Veterinarians recommend testing for heartworm infection before beginning heartworm preventive medication, at regular intervals after the dog is on a preventive medication and when dogs have clinical signs suggestive of heartworm disease. It is recommended and important that your pet be tested for heartworm infection/disease once per year.
How can my pet be treated?
Dogs: It is much better to prevent heartworms than to treat it (both for the dog and for your wallet). If your dog does become infected with heartworms, there is FDA-approved treatment available. There are risks involved in treating a dog for heartworms. Serious complications are much less likely in dogs that are otherwise in good health and when you carefully follow your veterinarian’s instructions.
The goal of heartworm treatment is to kill the adult worms and microfilariae present in your dog, as safely as possible. Keep in mind that the heartworms are dying inside the dog’s lungs. While your dog is treated, he/she will require complete rest throughout treatment and for a considerable time following treatment. (Very short leash walks only!) Additional medications may be necessary to help control the body’s inflammatory reaction as the worms die and are broken down in the dog’s lungs.
You should discuss with your veterinarian the options of treatment they will consider following the testing and further physical examination (X-rays, ultrasound) of your dog to determine the severity of the infestation and the overall health of your pet. Heartworm treatment is expensive and often times a pet owner cannot afford or a dog’s condition will not permit the full American Heartworm Society recommended guidelines. Only you and your veterinarian can decide what is best for you and your pet. Fully discuss all options available including but not limited to; AHS guidelines, surgery, double-shot, single shot (with slow-kill component) and slow-kill.
Cats: There is currently no effective and safe medical treatment for heartworm infection/disease in cats. If your cat is diagnosed with heartworms, your veterinarian may recommend medications to reduce inflammatory response and the result heartworm disease, or surgery to remove the heartworms.
For more information go to www.heartwormsociety.org.
THIS INFORMATION IS NOT IN ANY WAY INTENDED TO REPLACE THE NECESSITY OF BRINGING YOUR PET INTO A VETERINARIAN FOR AN EXAM FOR A MEDICAL DIAGNOSIS AND MEDICAL ADVICE. IF YOU ARE UNSURE IF YOUR PET HAS BEEN TESTED FOR HEARTWORMS OR IS NOT ON MEDICATION TO PREVENT HEARTWORMS, PLEASE CONTACT A VETERINARIAN AND SET UP AN APPOINTMENT FOR YOUR PET TO BE SEEN AS SOON AS POSSIBLE.