Prevalence of heartworm infection in cats with signs of cardiorespiratory abnormalities

Abstract

Objective - To determine prevalence of heartworm infection in a population of pet cats with cardiorespiratory abnormalities and to determine relative usefulness of clinical signs and tests in diagnosis of heartworm disease. Design - Prospective case series. Animals - 100 client-owned cats with clinical signs of cardiorespiratory abnormalities. Procedure - Cats were evaluated using CBC, modified Knott test, ELISA for serologic detection of heartworm antigen and antibodies to heartworms, thoracic radiography, and echocardiography. Cats were considered infected if they had circulating microfilaria, heartworm antigens in serum, or if heartworms were detected by echocardiography or on necropsy. Cats were considered suspicious for infection if they had 2 of the following: serum antibodies to heartworms, eosinophilia or basophilia, or indicative radiographic findings. Results - 9 cats were infected with heartworms, resulting in a prevalence of 9%; 26 cats had evidence of heartworm exposure (ie, serum antibodies to heartworms). Twenty cats were considered suspicious for heartworm infection. Some outdoor exposure was reported twice as often in heartworm-infected cats, compared with noninfected and suspicious cats. However, a third of infected cats were reportedly housed totally indoors. Cough and dyspnea were strong indicators of heartworm disease. Eight of 9 infected cats had serum antibodies to heartworms and heartworm antigen in serum. Thoracic radiography and echocardiography indicated heartworm infection in 6 and 7 of the 9 cats, respectively. Clinical Implications - Cough or dyspnea may indicate heartworm disease in cats; serologic tests, echocardiography, and radiography are most useful diagnostic procedures. Although living indoors is protective, it may not preclude heartworm infection in cats.