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Ancylostoma duodenale and
Necator americanus
Kallie McGettigan
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Hookworms
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http://animal.discovery.com/videos/monsters-inside-meflesh-eating-hookworm.html
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Facts:
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Commonly known as the hookworm
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576-740 million people in the world are infected
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Necator americanus was widespread in the Southeastern
United States until 20th century and was known as the
“American killer”
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Second most common human helminthic infection
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Taxonomy:
Kingdom: Animalia
Phylum: Nematoda
Class: Chromadorea
Order: Rhabditida
Family: Ancylostomidae
Genus: Ancylostoma
Necator
Species: duodenale
americanus
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Geographic Range
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Worldwide, most common in areas with warm, moist climates
and soil
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N. americanus commonly found in the Americas, Africa, India,
Southeast Asia, China and the Pacific Islands
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A. duodenale commonly found in Southeastern Europe, Northern
Africa, India, China, and Southeast Asia, also in small areas of the
U.S., Caribbean Islands, and South America
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Hosts
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Definitive Host: Humans
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Intermediate Host: None
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Morphology
Necator americanus
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The anterior end is curved dorsally giving them their “hook”
appearance
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Has a pair of dorsal and a pair of ventral cutting plates surrounding the
anterior margin of the buccal capsule. Also has a pair of subdorsal and
subventral teeth near the rear of the buccal capsule
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Males:
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7 to 9 mm long
have a copulatory bursa that’s diagnostic for the genus
The needle like spicules have minute barbs at their tips and are fused distally
Females:
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9 to 11 mm long
Vulva is located in middle of their body
Produce 5,000 to 10,000 eggs a day
Live for 3 to 5 years
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Morphology
Ancylostoma duodenale
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The anterior end is curved dorsally giving them their “hook”
appearance
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Has two ventral plates on the anterior margin of the buccal capsule that
each have two large teeth. They also have a pair of smaller teeth further
back in the capsule
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Males:
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8 to 11 mm long
Have a copulatory bursa characteristic to the species
Needle like spicules have simple tips and are not fused distally
Females:
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10 to 13 mm long
Vulva is located about a third of the body length from the posterior end
Can lay 10,000 to 30,000 eggs a day
Can live up to a year
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Life Cycle
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Life Cycle
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Eggs are passed in the stool, and hatch in 1 to 2 days when in warm moist conditions.
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The released rhabditiform larvae grow in the feces and soil.
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After 5 to 10 days and two molts they become filariform larvae that are infective.
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The infective larvae can survive 3 to 4 weeks in favorable environmental conditions.
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When contact occurs with a human host, the larvae penetrate the skin and are carried through
the blood vessels to the heart and then to the lungs.
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Then they penetrate into the pulmonary alveoli, up the bronchial trees to the pharynx and then
are swallowed.
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They end up in the small intestine, where they attach to the intestinal wall, where they ingest
blood.
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Most adult worms are eliminated in 1 to 2 years, but can survive for several years.
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Adult females release eggs which are then excreted in the feces.
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Pathology
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Small infections
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typically asymptomatic, less than 25 worms
Localized skin manifestations (“ground itch”) can occur during
penetration of the L3 larvae
Severe infections
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Anemia due to blood loss, can eventually lead to cardiac
complications
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In children, the lack of iron and protein can lead to growth
and developmental problems
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Gastrointestinal and nutritional symptoms can occur
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Respiratory symptoms can occur during the migration of the
larvae through the pulmonary system
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Diagnosis
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Identification of eggs in a fecal sample
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In light infections, a more concentrated sample is used by
performing a formalin-ethyl acetate sedimentation technique
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Use larvae to distinguish between the two worms, cannot tell
them apart by the eggs
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Treatment
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In countries where the infection is common and reinfection
is high, light infections are not treated
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In the U.S. mebendazole and albendazole are typically used
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Pyrantel pamoate is also used
Iron supplements are also given if infected person has
anemia
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Control and Prevention
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Avoid walking barefoot in
areas where infection is
common and where night soil
is used
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Avoid ingesting soil from these
areas
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Effective prevention includes
not defecating outdoors and
using effective sewage
disposal systems
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References
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http://www.cdc.gov/parasites/hookworm/
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http://dpd.cdc.gov/dpdx/HTML/Hookworm.htm
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http://animal.discovery.com/videos/monsters-insideme-flesh-eating-hookworm.html
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Roberts, L. Janovy, J. Foundations of Parasitology, 8th ed. New
York: McGraw-Hill, 2009.
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Quiz:
Which of these is a host?
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Which hookworm is able to cause
more damage with a few number
of worms present ?
 Necator
americanus
 Ancylostoma
duodenale
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Which order does the hookworm
belong to?
Piroplasmida
Trichurida
Rhabditida
Cyclophylidea
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Where do you find the adult
hookworms?
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Which stage of the life cycle is
infective?
 Rhabditiform
 Adult Worm
Larvae
 Eggs
 Filariform
Larvae