Necator americanus is a species of
hookworm (a type of
helminth) commonly known as the New World hookworm. Like other hookworms, it is a member of the phylum
Nematoda. It is a parasitic
nematode that lives in the small intestine of hosts such as humans, dogs, and cats.
Necatoriasis—a type of
helminthiasis—is the term for the condition of being host to an infestation of a species of
Necator. Since
N. americanus and
Ancylostoma duodenale (also known as Old World hookworm) are the two species of hookworms that most commonly infest humans, they are usually dealt with under the collective heading of "
hookworm infection". They differ most obviously in geographical distribution, structure of mouthparts, and relative size.