It is an infection caused by Ancylostoma or Necator.Ancylostoma duodenale and necator americanus are the main nematodes causing hookworm infection in  humans. he adult worm resides in the small intestine .In intestine they live in the jejunum where they get attached to the villi.The male worms are of 10 mm in length and the females vary from 10 to 13 mm in length.The eggs of these worms are passed in the faeces in thousands. One female ancylostoma duodenale produces  about 30,000 eggs  and female necator americanus produces about 9000 eggs per day. The production of eggs ensures the prominent exposure to the infection.The eggs which are passed out with the faeces are not infective to man.The eggs hatch in to the form of rhabditiform larvae under favourable conditions.These  larvae develop in to filiform larvae.These filiform larvae are infective to man. The  soil contaminated with infective larvae are the prominent source of infection.The mode of infection is like that the filiform larvae cast off their sheaths and then they penetrate the skin of the human host.The oral spears  found in the the anterior lobe  help these worms to penetrate  thesoft skinof the feet and hands through hair follicles.The incubation period  for necator americanus is 7 weeks and for ancylostoma duodenale  ranges from 5 weeks to 9 months.The main symptoms include  severe anaema.In children  with very prominent infection it may lead to retardation of mental and physical growth.Some toxins secreted from the worms head region causes  stomachache , food fermentation, diarrhea, constipation