Pulmonary Nodule Caused by Dirofilaria immitis in a Laboratory Rabbit (Oryctolagus cuniculus domesticus)

Abstract

Dirofilaria immitis (Leidy, 1856) is widely distributed throughout the world and has a wide range of hosts including carnivores, ungulates, primates, etc. Human dirofilariasis has been reported, e.g., Beaver and Orihel (1965, Am. J. Trop. Med. Hyg. 14: 1010-1029). In human cases, most of the lesions were observed in lungs and subcutaneous tissue. We detected a lung nodule, similar to human pulmonary dirofilariasis, in a female 7-month-old laboratory rabbit. The animal was one of 172 rabbits used in a nonrelated toxicological study. The nodule was detected just beneath the dorsal surface of the right cranial lobe of the lung. It was sharply circumscribed from surrounding tissue. Neither necrotic nor hemorrhagic change was observed in any other part of the lung. Lung tissue, including the lesion, was fixed in 10% neutral formalin and embedded in paraffin. Sections were stained with hematoxylin-eosin and Heidenhain's azocarmine (Azan). A piece of formalin-fixed lung lesion was dissected carefully using stereoscopic microscopy and a fragment of worm was collected and treated with lactophenol solution. Although serum of this rabbit was examined immunologically by the Ouchterlony technique using crude D. immitis antigens, no pr cipitation was observed. Microscopically, the nodule was an organized embolus surrounding the worm in a pulmonary artery (Fig. 1). Several sections of parasite were surrounded by an organized