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146 CHAPTER 6

LIFE CYCLE of—
Hookworm

Swallowed
Pharynx Attached to
small intestine
Trachea

Lungs
Adults in
small intestine
Circulation
MAN

Penetrates skin

Eggs in feces
Filariform larva (diagnostic stage)
(infective stage)

Source: Centers for Disease Control and Prevention (CDC)
EXTERNAL ENVIRONMENT

Rhabditiform larva
hatches

Rhabditiform larva in soil

(occasionally in old feces)

FIGURE 6-5 Life cycle for human hookworms, which includes two nematode (roundworm) species, Ancylostoma
duodenale and Necator americanus

of selling small bags of white clay to satisfy these cravings. Hookworm infections begin with larval invasion
Prolonged constipation followed by diarrhea, palpita- of the skin, particularly the lower extremities and feet.
tions, thready pulse, coldness of the skin, pallor of the The lesions resemble bites of spiders and insects, and
mucous membranes, fatigue and weakness, and shortness may produce blistering typically cause intense itch-
of breath may occur in long-standing cases. The extremely ing (pruritis) that is called “ground itch” or “toe itch.”
grave medical conditions such as dysentery, hemorrhage, and may be accompanied by racking coughs, chest pain,
and edema may culminate in fatal consequences in cases wheezing, and fever for some people who have been ex-
of hookworm infections that are untreated. posed to extremely high levels of larvae. Epigastric pains,