Gongylonema pulchrum is the only parasite of the genus Gongylonema capable of infecting humans.Gongylonema pulchrum infections are due to humans acting as accidental hosts for the parasite. There are seven genera of spirudia nematodes that infect human hosts accidentally: Gnathostoma, Thelazia, Gongylonema, Physaloptera, Spirocerca, Rictularia. The G. pulchrum parasite is a nematode worm of the order Spirurida. It is a relatively thin nematode, and like other worms within its class, it has no circulatory or respiratory system. Most other Gongylonema species infect birds and mammals: there are 25 species found in mammals and 10 species found in birds.