The causative agent of toxocariasis (canine roundworm) belongs to the type Nemathelminthes, class Nematodes, suborder Ascaridata, genus Toxocara. T. canis is a dioecious nematode, sexually mature individuals of which reach relatively large sizes (the length of the female is 9-18 cm, the male - 5-10 cm). Toxocara eggs are spherical, 65-75 microns in size. T. canis parasitizes dogs and other representatives of the canine family.