Page 486 - Review of Medical Microbiology and Immunology ( PDFDrive )

mebooksfree.com
mebooksfree.com

mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com mebooksfree.com Circulation Lungs Trachea mebooksfree.com mebooksfree.com mebooksfree.com
475
CHAPTER 56 Nematodes
Ascariasis
(Ascaris lumbricoides)

Pharynx

Swallowed
mebooksfree.com
mebooksfree.com mebooksfree.com Ingested Larvae hatch Human mebooksfree.com mebooksfree.com mebooksfree.com

in intestine

Adults in lumen
of small intestine

Eggs in feces

Embryonated egg
with 2nd stage larva
(infective stage) (Diagnostic stage) Fertilized
1-cell
mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com

External Environment

mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com the blood loss. “Ground itch,” a pruritic papule or vesicle, mebooksfree.com
mebooksfree.com
2-cell
Advanced
stage
cleavage
FIGURE 56–6
Ascaris lumbricoides. Life cycle. Top: Blue arrow at top left shows eggs being ingested. Larvae emerge in the intestinal tract,
enter the bloodstream, and migrate to the lungs. They then enter the alveoli, ascend into the bronchi and trachea, migrate to the pharynx, and
are swallowed. Adult Ascaris worms form in small intestine. Eggs pass in human feces. Bottom: Red arrow indicates maturation of eggs in the
soil. (Figure courtesy of Public Health Image Library, Centers for Disease Control and Prevention.)
into third-stage, infectious, nonfeeding (filariform) larvae
(see Figure 56–2E), which penetrate the skin to complete
can occur at the site of entry of the larvae into the skin. The
the cycle.
Pneumonia with eosinophilia can be seen during larval
migration through the lungs.
Pathogenesis & Clinical Findings human hookworms also cause cutaneous larva migrans.
The major damage is due to the loss of blood at the site of
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com In the United States, Necator is endemic in the rural south- mebooksfree.com
mebooksfree.com
Epidemiology
attachment in the small intestine. Up to 0.1 to 0.3 mL per
worm can be lost per day. Blood is consumed by the worm
Hookworm is found worldwide, especially in tropical areas.
and oozes from the site in response to an anticoagulant
ern states. Walking barefooted on soil predisposes to infec-
made by the worm. Weakness and pallor accompany the
microcytic anemia caused by blood loss. These symptoms
tion. An important public health measure was requiring
children to wear shoes to school.
occur in patients whose nutrition cannot compensate for

mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com