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Heartworm Disease In Dogs


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Canine heartworm disease is transmitted from dog to dog via mosquitoes that carry a microscopic, parasitic, juvenile worm of Dirofilaria immitis. As the mosquito is taking a blood meal these microscopic larvae are deposited on the dog’s skin and ultimately invade the dog’s bloodstream. After migrating to the right side of the dog’s heart they develop into adult worms that can grow to be 10 to 12 inches in length. The end result of this infestation can be lung disease, heart failure and death.dog photo


Some dogs can be infected for many years before symptoms develop. As the adult heartworms live and thrive in the right side of the heart they cause damage to the heart muscle and lung arteries. Early signs of the disease include a mild persistent cough, reluctance to exercise, fatigue after moderate exercise, decreased appetite and weight loss. Over time, the blood flow through the diseased lungs becomes diminished and some dogs develop heart failure.


Currently, the most accurate method to detect heartworm disease in dogs is a simple blood test. At our clinic this test is commonly performed in conjunction with a screen for three common tick-born diseases. This test cannot detect infection until the heartworms are at least six months old. We may also recommend X-rays or an ultrasound image to help us diagnose heartworm disease. These blood tests may be repeated at regular intervals depending on your dog’s medical history or exposure level to the disease. All dogs over six months old need to be tested prior to starting any preventative program. We recommend retesting after any lapse in administration of preventative as many heartworm preventatives can cause life-threatening adverse reactions and even death if administered to dogs that test positive to heartworms.


It is fair to say that once a dog is diagnosed with heartworms, if left untreated, the disease will worsen and may lead to more serious illness and even death. Unless there are medical reasons not to treat a particular dog, all heartworm-positive dogs need to be treated. The other side of the coin is that treating dogs for heartworms can also lead to complications as these dead parasites may cause further injury to the lungs and pulmonary arteries. Before any treatment regimen is undertaken we will perform a thorough physical examination, a complete blood screen and fecal test to assess your dog’s level of risk. To reduce complications we will also educate you in detail before beginning treatment.


Heartworm preventatives are extremely effective when given on a proper and timely schedule. It is important to note that most of these drugs do not linger in the dog’s system and are quickly eliminated from the body. They work by eliminating infections acquired since the last dose. All of the currently approved preventatives are safe, highly effective, and relatively inexpensive. In addition, they usually provide protection against other parasites such as intestinal worms, ticks, fleas, mange and lice. We currently recommend your dog be on prevention year-round in order to eliminate the risk of heartworm infection. Prevention is always safer and more affordable than treating your dog with an adult heartworm infestation.


Since this short article cannot cover every aspect of heartworm disease and treatment in dogs we suggest you visit the website of the American Heartworm Society (www.heartwormsociety.org). Here you will find more in-depth information regarding prevention, diagnosis and treatment of heartworm disease. In addition, our doctors and staff are always available to answer your questions concerning this debilitating and potential fatal disease.


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