Canine Dirofilarial Hemoglobinuria Induced by Milbemycin D Administration

Abstract

Eight of 85 microfilaria positive dogs developed dirofilarial hemogloginuria (caval syndrome) after oral administration of milbemycin D. The onset was confirmed from 3 to 24 hr after administration. These dogs recovered whithout treatment from 21 to 117 hr after the onset. The findings at the time of the onset were systolic cardiac murmur, positive jugular pulse, irregular heart beat, decrease of heart rate, fall of blood pressure, occurrence of filarial echoes at the tricuspid valve orifice, ventricular to atrial premature heart beat, decrease of circulating microfilariae, increases of serum enzyme activities and plasma hemoglobin concentration and hemoglobinuria. The number of adult heartworms ranged from 10 to 39, and the number of worms per kg of body weight from 1.00 to 8.67. It did not always follow that a large number of heartworms caused the onset of dirofilarial hemoglobinuria. Serum and erythrocyte lipid findings were similar to those in chronic serious dirofilariasis, suggesting a tendency to be easily injured in erythrocytes already at the time of the onset. It was suggested that the suppression of cardiac functions may cause the migration of heartworms from the pulmonary arteries towards the venae cavae.