Dirofilaria presenting as orbital mass.

Dirofilaria is a common roundworm infection of dogs, cats, raccoons, and other animals that is commonly referred to as "heartworm." The genus Dirofilaria includes D. immitis, which is a common cause of animal disease in the western hemisphere and primarily manifests as pulmonary lesions in humans, and D. repens, which is the more common causative agent of animal disease in Eurasia and primarily results in subcutaneous and ocular lesions in humans. Humans are accidental end hosts, with infection resulting from bites by mosquitoes of the Culicidae family in which ingested microfilaria have matured to infectious larvae.