Dog Heartworm Treatment

The Diagnosis of Canine Heartworm Disease

The diagnosis of canine heartworm disease depends upon the following:

The diagnosis procedures include :

Serology. This is a diagnostic tests for the study of antibodies and antigens in blood serum.

Antigen Tests. Antigen tests detect specific antigens from adult female heartworms, and are used with much success to detect canine heartworm infection. Currently, tests are available as in-clinic tests, as well as at many veterinary reference laboratories. Most commercial tests will accurately detect infections with one or more mature female heartworms that are at least seven or eight months old, but they generally do not detect infections of less than five months duration.

Antibody Tests. Although Necropsy (Autopsy: examination after death) is probably the most definitive diagnostic test, it is hoped that it never reaches that stage. Heartworms are usually found in the right ventricle of the heart or in the major pulmonary arteries, at times in its farthest branches. Occasionally heartworms may be found in organs other than the heart and lungs but such infections are rare.

Physical Examination. A physical examination may appear to be perfectly normal in heartworm-infected dogs with mild disease. Severely affected dogs, however, may demonstrate right-sided heart failure. Labored breathing or crackles may be heard in the lungs due to vascular clots and elevated pressure. A history of chronic cough and exercise intolerance are among the earliest detectable abnormalities. Tachycardia (rapid heartbeat), ascites (fluid in the abdomen) and hepatomegaly (enlarged liver) indicate right-sided congestive heart failure. Hemoptysis (blood in the sputum) occasionally occurs and indicates severe thromboembolic (clots) complications within the lungs. Anorexia (loss of appetite), cachexia (severe weight loss), syncope (fainting) jaundice or yellow bile pigmentation present in the skin and mucus membranes may appear in severely affected dogs. Occasionally, heartworms are reported in atypical locations such as the eyes, abdominal cavity, cerebral artery and spinal cord. Clinical signs and disease experienced in such infections depend largely on the location of the worms. The primary response to the presence of heartworms in dogs, however, occurs in the heart and lungs.

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.

Angiography and Ultrasonography. These forms of imaging are rarely used in the diagnosis of canine heartworm infection outside of referral practices and teaching institutions. Angiography is a technique that permits visualization of blood vessels in the body by taking radiographs within seconds after injecting a contrast material (dye) into those blood vessels. In canine heartworm infection, angiography is used to study changes to the pulmonary arteries and worms may be visualized as filing defects on the angiogram. Ultrasonography (echocardiography) has been used to evaluate enlargement of the heart chamber and to look for the presence of heartworms in the right ventricle or main pulmonary artery.

Microfilarial Detection and Differentiation. The identification of the offspring (microfilaria) of heartworms (Dirofilaria immitis) from a blood sample indicates infection with adult heartworms. Identifying such offspring can also be accomplished through either one of two concentration tests: the modified Knott’s test (a technique requiring spinning the blood sample in a mechanical device called a centrifuge) or a filter test. Practitioners will often do a quick examination of a blood smear to look for the presence of the offspring (microfilaria), but this procedure is not sensitive enough to rule out their absence in a sample. If they are present, it is a definitive diagnosis for the presence of adult heartworms. One other parasite infection of dogs is capable of producing circulating microfilariae, detected on examination of the blood. Acanthocheilonema (dipetalonema) reconditum (a genus of filarial nematodes) is a non-disease causing parasite that localizes in the tissues beneath the skin of dogs. Its offspring can be differentiated from those produced by heartworms through microscopic examination evaluating size, shape and their ability to move spontaneously.