Dirofilaria is a genus of nematodes, or roundworms, in the family Onchocercidae. Some species cause dirofilariasis, a state of parasitic infection, in humans and other animals. There are about 27 species in the genus. These are generally divided into two subgenera, Dirofilaria and Nochtiella. Some species are well-known parasites, including Dirofilaria immitis, the dog heartworm, Dirofilaria repens, which affects many types of nonhuman mammals, and Dirofilaria tenuis, which usually parasitizes raccoons, but can infect humans, as well.