Ancylostomiasis-- Hookworm Infection
Source: Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of
"Hookworm is an intestinal parasite of humans that usually causes mild diarrhea or cramps.... You can
become infected by direct contact with contaminated soil, generally through walking barefoot, or
accidentally swallowing contaminated soil..."
Necator americanus ------------------------------- Hookworms,
Hookworm is the common name for blood-sucking nematodes of the Ancylostomatidae family; the 2 species
that most commonly infect humans are Ancylostoma duodenale and Necator americanus.
Members of the Ancylostoma genus cause the following 3 clinical entities in humans:
Classic hookworm disease is a gastrointestinal (GI) infection with chronic blood loss leading to iron
deficiency anemia and protein malnutrition. The disease is caused by A duodenale, the major anthropophilic
hookworm, and, less commonly, by the zoonotic species Ancylostoma ceylanicum.
Cutaneous larva migrans is an infection caused most commonly by larvae of Ancylostoma braziliense,
whose definitive hosts include dogs and cats. The manifestations of cutaneous larva migrans are limited to
Eosinophilic enteritis is a GI infection caused by the dog hookworm Ancylostoma caninum. The disease is
characterized by abdominal pain but no blood loss.
N americanus causes only "classic hookworm disease," as defined above.
Larvae require about 6-8 weeks from the time of skin penetration to develop into adults. Worms mate in the
small intestine, and the females deposit fertilized eggs into the lumen. Eggs begin to appear in feces about
8-12 weeks after infection.
Some A duodenale larvae, however, may undergo a period of extraintestinal dormancy after penetrating the
skin before resuming their migration to the gut for maturation. This dormancy period can last weeks or
months. As a result of this dormant period, intestinal ancylostomiasis can occur up to a year after initial
exposure to infective larvae. The repositories of these dormant larvae may be muscle tissue, or the
dormant larvae may enter the mammary glands and breast milk, which may account for cases of infantile
ancylostomiasis in Africa, China, and India.
As is true with most helminthic infections in endemic areas, relatively few persons carry heavy parasite
burdens, although hookworm disease may be fatal, especially in infants.
In endemic areas, highest prevalence is among school-aged children and adolescents, which may be
because of age-related changes in exposure and the acquisition of immunity.
Once infected, children are more vulnerable to developing morbidity because dietary intake often fails to
compensate for intestinal losses of iron and protein, especially in developing countries.
A fulminant form of acute GI hemorrhage associated with acute ancylostoma infection has been described
hookworm infection, Ancylostomatidae, ancylostomiasis, Necator americanus, N americanus, A duodenale,
Ancylostoma duodenale, ground itch
Human hookworm infection is a common soil-transmitted helminth infection that is caused by the nematode
parasites, Necator americanus and Ancylostoma duodenale. Worldwide, hookworm infects an estimated 740
million people, most of whom are asymptomatic. Despite this lack of symptoms, hookworm substantially
contributes to the incidence of anemia and malnutrition in developing nations.
The life cycle of hookworms begins with the passing of hookworm eggs in human feces and their
deposition into the soil (see Image 1 for the hookworm life cycle). Larval growth is most proliferative in
favorable soil that is sandy and moist, with an optimal temperature of 20-30°C. Under these conditions, the
larvae hatch in 1 or 2 days to become rhabditiform larvae, also known as L1.
Infection of the human host is established when filariform larvae penetrate the skin, typically on the hands
or feet. This penetration may cause a local pruritic dermatitis, also known as ground itch. The larvae migrate
through the dermis, entering the bloodstream and moving to the lungs within 10 days
Once in the lungs, the hookworms penetrate the alveoli and are carried to the glottis by means of the ciliary
action of the respiratory tract. During pulmonary migration, the host may develop a mild reactive cough,
sore throat, and fever that resolve after the worm migrates into the intestines. At the glottis, the larvae are
swallowed and carried to their final destination, the small intestine.
Intestinal blood loss secondary to infection is the major clinical manifestation of hookworm infection. In
fact, hookworm disease historically refers to the clinically significant hypochromic, microcytic anemia and
the depletion of iron stores resulting from chronic intestinal blood loss secondary to hookworm infection.
The mortality rate is low and likely underrecognized because of its insidious nature.
Anemia remains the most significant clinical implication of hookworm disease. Because of chronic
reinfection, hypoproteinemia, weight-loss, edema, and anasarca may also occur.
See also Special Concerns.
Although children bear a large disease burden, hookworm infection appears to have an atypical distribution
of infection by age. Unlike other soil-transmitted helminth infections, such as those due to Ascaris or
Trichuris organisms, for which the incidence peaks in childhood, hookworm infection appears to continue
to increase throughout childhood until it reaches a plateau in adulthood.