Hookworms are intestinal, blood-feeding, parasitic roundworms that cause types of infection known as helminthiases. In humans, hookworm infections are caused by two main species of roundworm belonging to the genera Ancylostoma, and Necator. In other animals the main parasites are species of Ancylostoma.
Dogs are commonly infected by Ancylostoma caninum.
The two common species that infect humans share a similar morphology. A. duodenale worms are pale grey or slightly pink. The head is bent a little in relation to the rest of the body, forming a hook shape – hence the name. The hook is at the front end of the body. They have well-developed mouths with two pairs of teeth. Males measure approximately one centimeter by 0.5 millimeter, and females are often longer and stouter. Males also have a prominent copulatory bursa posteriorly.
N. americanus is generally smaller than A. duodenale with males usually 5 to 9 mm long and females about 1 cm long. Instead of the two pairs of teeth in A. duodenale, N. americanus has a pair of cutting plates in the buccal capsule. Also the hook is much more defined in Necator americanus.
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