human hookworms include two nematode (roundworm) species, Ancylostoma
duodenale and Necator americanus. (Adult females: 10 to 13
mm (A. duodenale), 9 to 11 mm (N. americanus); adult
males: 8 to 11 mm (A. duodenale), 7 to 9 mm (N. americanus).
A smaller group of hookworms infecting animals can invade and parasitize
humans (A. ceylanicum) or can penetrate the human skin (causing
cutaneous larva migrans), but do not develop any further (A.
braziliense, A. caninum, Uncinaria stenocephala).
Occasionally A. caninum larva may migrate to the human intestine
causing eosinophilic enteritis; this may happen when larva is ingested
rather than through skin invasion.
Eggs are passed in
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 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. In addition, infection
by A. duodenale may probably also occur by the oral and
transmammary route. N. americanus, however, requires a
transpulmonary migration phase.
second most common human helminthic infection (after ascariasis).
Worldwide distribution, mostly in areas with moist, warm climate. Both
N. americanus and A. duodenale are found in Africa, Asia
and the Americas. Necator americanus predominates in the
Americas and Australia, while only A. duodenale is found in the
Middle East, North Africa and southern Europe.
deficiency anemia (caused by blood loss at the site of intestinal
attachment of the adult worms) is the most common symptom of hookworm
infection, and can be accompanied by cardiac complications.
Gastrointestinal and nutritional/metabolic symptoms can also occur. In
addition, local skin manifestations ("ground itch") can occur during
penetration by the filariform (L3) larvae, and respiratory symptoms can
be observed during pulmonary migration of the larvae.
Microscopic identification of eggs in the stool is the most common
method for diagnosing hookworm infection. The recommended procedure is
specimen in 10% formalin.
using the formalin–ethyl acetate sedimentation technique.
Examine a wet
mount of the sediment.
concentration procedures are not available, a direct wet mount
examination of the specimen is adequate for detecting moderate to heavy
infections. For quantitative assessments of infection, various methods
such as the Kato-Katz can be used.
comparison with other intestinal parasites
Examination of the
eggs cannot distinguish between N. americanus and A. duodenale.
Larvae can be used to differentiate between N. americanus and
A. duodenale, by rearing filariform larvae in a fecal smear on a
moist filter paper strip for 5 to 7 days (Harada-Mori). Occasionally,
it may be necessary to distinguish between the rhabditiform larvae (L2)
of hookworms and those of Strongyloides stercoralis.
In countries where
hookworm is common and reinfection is likely, light infections are often
not treated. In the United States, hookworm infections are generally
treated with albendazole*. Mebendazole* or pyrantel pamoate* can also
* This drug is
approved by the FDA, but considered investigational for this purpose.