Subcutaneous and cardiopulmonary dirofilariasis in a dog.

Canine subcutaneous dirofilariasis is rare and typically caused by Dirofilaria repens. An adult male, intact, mixed breed dog from South Carolina, USA, was examined because of physical trauma to the right maxilla. The dog died during hospitalization and was submitted for necropsy. Gross post-mortem changes included approximately 150 adult nematodes morphologically consistent with Dirofilaria spp. in the pulmonary artery, right atrium, and right ventricle. Histologically there was widespread proliferative pulmonary endarteritis with intraluminal nematodes morphologically consistent with Dirofilaria spp. Four similar nematodes were present in the subcutaneous tissue of the left medial thigh and tibial area. These nematodes were located within the fascia and skeletal muscles. They were surrounded by epithelioid macrophages and multinucleated giant cells, with some lymphocytes and plasma cells, and areas of mineralization (interpreted as mineralized cross sections of nematodes). Nematodes were morphologically identified as D. immitis. Subcutaneous dirofilariasis caused by D. immitis occurs when migrating nematode larvae develop into adults in the subcutaneous and skeletal muscle tissues. Key clinical message: Subcutaneous dirofilariasis in dogs is rare and most often associated with Dirofilaria repens. This case highlights the pathology findings of subcutaneous D. immitis in a dog.