According to the American Heartworm Society, only 50 percent of all dogs are protected by heartworm medicine in areas highly infected with heartworm. Although some areas have a lower rate of heartworm infection, heartworm isn't limited to dogs in warmer climates as it has been found in all 50 states. Because heartworm is a fatal disease, owners need to ensure their pets are protected by getting them tested for heartworm, in addition to protecting them with monthly medications.
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Identification and Diagnosing Heartworm Disease
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Heartworm testing is done to test for heartworm disease, which is a canine infection of the roundworm known as Dirofiaria immitis. This parasitic worm lives in a dog's pulmonary arteries, which carry blood from the heart to the lung. Clinical signs are observed. The owner must provide an accurate patient history. Diagnostic procedures are done including blood testing, a physical exam, X-rays, an ultrasound, angiography and testing for heartworm.
Direct Blood Smear Tests
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Direct blood smear tests involve examining a drop of blood for the presence of live microscopic microfilaria (baby heartworms). Detecting only one baby heartworm indicates the likelihood of a large number of them. According to an article published by Mar Vista Animal Center in Los Angeles, California, this type of heartworm testing requires large numbers of larvae because less than 20 to 50 baby heartworms per millimeter of blood will not be detected. This type of test is simple; however, it isn't as accurate as other tests.
Filter Tests
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In testing for heartworms, a blood sample is examined on a microscope slide to look for microscopic baby heartworms. Once a blood sample is obtained, it's examined and treated with a chemical that breaks down the blood cells. In filter testing, the treated blood sample is forced through a filter that traps the heartworms. Then microscopic analysis is done on the filter.
The Knott's Test
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The Knott's Test is done by placing a chemical in the dog's bloodstream that breaks down the blood cells. This process helps locate a heartworm infestation. The treated blood sample spins in a centrifuge, which is a mechanical device. The upper portion of the separated blood is poured out, and the contents found at the bottom of the tube are examined microscopically to determine if there are heartworms.
Heatworm Serology
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Heartworm serology are tests for proteins in the bloodstream produced by adult heartworms. An accurate and sensitive test, heartworm serology is done on all dogs for ruling out heartworm infection. Some dogs that receive a negative report for baby heartworms may still have adult heartworms found from a serology. This type of infection is known as hidden or occult heartworm infection. Heartworms can be hidden for several reasons. For example, they can be young and sexually immature. There can be a single sex infection, such as all female or all male worms. On the other hand, a dog can be on medicines resulting in the female heartworms being infertile. An example would be dogs taking low doses of ivermectin.
Considerations
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Because heartworm disease can't be detected until seven months following an initial infestation, dogs younger than seven months old shouldn't be tested, according to petplace.com. Also, dogs not receiving any heartworm preventative every month throughout the year need to be retested before receiving more medication. It's also recommended for owners to retest a dog when it changes preventative medications.
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