Hookworm is a parasite that lives in the small intestine of its host, which may be a mammal such as a cat, dog, or human. Two species of hookworms commonly infect humans. The distribution of each species significantly overlaps that of the other. Necator americanus predominates in The Americas and Australia, while only A. duodenale is found in the Middle East, North Africa and southern Europe. Hookworms are thought to infect 800 million people worldwide. The A. braziliense and A. tubaeforme species infect cats, while A. caninum infects dogs. Uncinaria stenocephala infects both dogs and cats. These worms are much smaller than the large roundworm, Ascaris lumbricoides, and the complications of tissue migration and mechanical obstruction so frequently observed with roundworm infestation are less frequent in hookworm infestation. The most significant risk of hookworm infection is anemia secondary to loss of iron and protein into the gut.