Necator americanus & Ancylostoma duodenale

Phylum: Nemathelminthes
Class: Nematoda
Order: Strogylata
Species: Necator americanus, Ancylostoma duodenale

Geographical Distribution

• N. americanus is usually found in moist Tropical regions such as South East Asia, Africa and America.
• A. doudenale is found in dryer and colder regions like North India, Pakistan, North China, Middle East and North Africa.

Morphology

• Adults are cylindrical with head bent sharply backward (hooked appearance).
• The male is smaller and possess a bursa at the posterior end.
• The eggs of various species are indistinguishable.
• Eggs are ovoid with thin transparetn shell.
• Size of eggs: 75 um x 36 um.
• When passed in the host intestine, they are single celled.
• In the faeces, they are at 4 - 8 celled stage.

hookworm egg

  

Ancylostoma duodenale	Necator americanus
First identified in Italy	First identified in Texas, USA
Old world hookworm	New world hookworm
Larger (male 8-11mm)	Smaller (male 7-9mm)
Anterior end bent in same direction of general curvature of body	Anterior end bent in opposite direction of general curvature of body
Prominent buccal capsule with 2 pairs of teeth	Smaller buccal capsule with 2 pairs of semilunar cutting plates
Vulva opens at junction of middle and posterior 1/3	Vulva opens a little in front of the middle
Copulatory spicules not fused	Copulatory spicules fused at ends to form a barbed tip
Lifespan 2-7years	Lifespan 4-20yrs
Ground itch less common	Ground itch more common

Hookworm Life Cycle

• Eggs are passed in the stool, and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days.
• The released rhabditiform larvae grow in the feces and/or the soil, and after 5 to 10 days (and two molts) they become become filariform (third-stage) larvae that are infective.
• These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. On contact with the human host, the larvae penetrate the skin and are carried through the veins to the heart and then to the lungs.
• They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed.
• The larvae reach the small intestine, where they reside and mature into adults.  Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host.
• Most adult worms are eliminated in 1 to 2 years, but longevity records can reach several years.