Page 488 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com Swallowed small intestine CHAPTER 56 Nematodes 477 mebooksfree.com
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Hookworm infection
(Ancylostoma duodenale,
Necator americanus)
y r a
h
P
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o t d
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a t t A
Trachea
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Lungs
Circulation

Eggs in feces

Filariform larva
(Infective stage)
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External Environment

Rhabditiform larva
hatches

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cycle within humans. mebooksfree.com
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FIGURE 56–9
Hookworms (Necator and Ancylostoma). Life cycle. Top: Blue arrow on left shows filariform larvae penetrating skin. Larvae
migrate through lung and may cause pneumonia. Adult hookworms attach to intestinal mucosa and cause bleeding and anemia. Eggs pass in
human feces. Bottom: Red arrow indicates maturation of eggs in the soil to form rhabditiform larvae and then infective filariform larvae. (Source:
Public Health Image Library, Centers for Disease Control and Prevention.)

contact skin, they penetrate and again initiate the parasitic
occur at the site of larval penetration of the skin, as with
hookworm. Strongyloides stercoralis also causes cutaneous
larva migrans.
Pathogenesis & Clinical Findings
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Autoinfection can result in chronic strongyloidiasis
Most patients are asymptomatic, especially those with a low
characterized by intermittent abdominal pain, fluctuating
rashes, and intermittent eosinophilia. In hyperinfection,
worm burden. Adult female worms in the wall of the small
intestine can cause inflammation, resulting in watery diar-
intestinal mucosa that sepsis caused by enteric bacteria,
rhea. Larvae in the lungs can produce a pneumonitis simi-
lar to that caused by Ascaris. Pruritus (ground itch) can
such as Escherichia coli and Bacteroides fragilis, can occur.

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