Necator americanus, the New World hookworm, is a soil-transmitted helminth whose infective form is the filariform (third-stage, L3) larva that develops in warm moist soil from eggs shed in stool. The single accepted portal of entry is active percutaneous penetration — the larva drills through unbroken skin, typically of the foot in people walking barefoot.
Once in, the larva follows the heart-lung migration: skin venule $\rightarrow$ right heart $\rightarrow$ pulmonary capillaries $\rightarrow$ alveoli $\rightarrow$ bronchi/trachea $\rightarrow$ swallowed $\rightarrow$ small intestine, where it matures into a blood-sucking adult and produces chronic iron-deficiency anaemia.
Contrast: Ancylostoma duodenale can additionally be acquired orally, but Necator is acquired only by the transcutaneous route. Egg ingestion ($\rightarrow$ Ascaris/Trichuris), sandfly bite ($\rightarrow$ Leishmania), and cyst-containing pork ($\rightarrow$ Taenia) are routes for entirely different organisms.
\[\boxed{\text{Necator americanus infects by skin penetration of filariform larvae}}\]