Hookworms can be divided into many types, and there are certain differences between the hookworms infected by cats and dogs. Cats are infected with hookworms such as Ancylostoma caninum, Ancylostoma brasiliensis, Ancylostoma stenosocephalum and Ancylostoma canis. Among them, Ancylostoma canis and Ancylostoma canis are the most common, often parasitizing the duodenum of cats. ​​​​​​

Canine hookworm is a small, light yellowish-white nematode with its head end slightly bent toward the back and a well-developed mouth pouch. There are three pairs of symmetrical large teeth arranged on its front and ventral surface, and each tooth is curved inward like a hook. Male worms are 9 to 12 mm long, and female worms are 10 to 21 mm long. The eggs are colorless, oval-shaped, with blunt ends. Fresh eggs contain 2 to 8 egg cells. Adult worms parasitize in the small intestine (especially the duodenum) and lay eggs. The eggs are excreted with the feces. Under appropriate conditions, the larvae hatch in 12 to 13 hours, and then molt into infective larvae in about 1 week.

Infectious larvae can crawl along wet grass and cage walls. Infectious larvae can infect the host through the mouth, skin and placenta. When the larvae enter the host's body through the mouth, they stay in the intestines and gradually develop into adult worms. When the larvae invade through the skin, they burrow into peripheral blood vessels, follow the blood flow to the right heart, and then along the small circulation to the lungs, penetrate the capillaries and lung tissue, migrate to the alveoli and small bronchi, and then reach the trachea and bronchi. It enters the mouth with phlegm, is swallowed with saliva, and then develops into adult worms on the wall of the small intestine.