Verminous vasculitis, pneumonia and pulmonary infarction in a cynomolgus monkey after treatment with ivermectin

An apparently healthy cynomolgus monkey (Macaca fascicularis) died 2 hours after routine inhalation anesthesia and implantation of a femoral catheter. Gross necropsy findings included patchy raised areas of severe pulmonary hemorrhage and consolidation. Filarioid nematodes (Edesonfilaria malayensis) were located in pulmonary blood vessels and in numerous 0.1-2 cm fibrous cysts on the pleural surfaces of the lungs, pericardium, diaphragm, retroperitoneum, and in the urinary bladder wall. Microscopic lesions included verminous vasculitis, pulmonary infarcts and pneumonia. Many of the nematodes were more necrotic than the surrounding host tissue. During quarantine, 17 days before surgery, the monkey had been given a single dose of ivermectin (200 micrograms/Kg, intramuscular) as an anthelminthic for gastrointestinal nematodes. It is postulated that many of the filarioid nematodes were killed by this treatment. These parasitic emboli caused pulmonary infarction and the severe inflammatory reaction. The resulting pulmonary disease compromised pulmonary function and contributed to death after anesthesia. This complication should be considered if monkeys possibly harboring filarioid nematodes are treated with ivermectin.