Hematologic and radiographic changes in cats after inoculation with infective larvae of Dirofilaria immitis

Hematologic and radiographic findings in 15 domestic cats inoculated with 25, 100, or 200 to 400 infective larvae of Dirofilaria immitis and in 5 uninoculated cats were compared. Eosinophilia and leukocytosis developed 3 to 5 months after inoculation; packed cell volume and hemoglobin values were similar for inoculated cats and controls. Changes detected in radiographs of inoculated cats were: (1) increased visualization of the pulmonary arteries; (2) right-side cardiac enlargement; and (3) diffuse to focal areas of density in the pulmonary parenchyma. At least one of these lesions was visible radiographically by 3 to 7 months after inoculation in all 15 cats. The severity of changes was not directly proportional to the number of infective larvae inoculated, adult worm burden, or age of cat. However, male cats had more severe cardiopulmonary lesions than did females, and cats that had microfilaremia during the course of infection had more severe pulmonary lesions, as determined radiographically. Parenchymal densities decreased in 8 of the 15 inoculated cats 6 to 14 months after inoculation. Cardiac enlargement was detected radiographically in 10 of the inoculated cats. Enlargement of the pulmonary arteries was the most consistent sign of D immitis infection; it developed and persisted in 12 cats found to be infected at necropsy.