Page 485 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com Pathogenesis & Clinical Findings mebooksfree.com mebooksfree.com
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PART VI Parasitology
474
The major damage occurs during larval migration rather
than from the presence of the adult worm in the intestine.
The principal sites of tissue reaction are the lungs, where
inflammation with an eosinophilic exudate occurs in
response to larval antigens. Because the adults derive their
nourishment from ingested food, a heavy worm burden
may contribute to malnutrition, especially in children in
developing countries.
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mebooksfree.com mebooksfree.com mebooksfree.com result from the presence of adult worms in the intestine. mebooksfree.com
Most infections are asymptomatic. Ascaris pneumonia
with fever, cough, and eosinophilia can occur with a heavy
larval burden. Abdominal pain and even obstruction can
FIGURE 56–4
Enterobius vermicularis—eggs. Long arrow
Epidemiology
points to an egg of the pinworm, E. vermicularis recovered on
Ascaris infection is very common, especially in the tropics;
“Scotch tape”. Short arrow points to the embryo inside the egg.
hundreds of millions of people are infected. In the United
(Source: Public Health Image Library, Centers for Disease Control and Prevention.)
Laboratory Diagnosis
water contaminated with human feces (Figures 56–3C and States, most cases occur in the southern states.
Diagnosis is usually made microscopically by detecting
56–7). The eggs hatch in the small intestine, and the larvae
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mebooksfree.com mebooksfree.com mebooksfree.com sees adult worms in the stools. mebooksfree.com mebooksfree.com
eggs in the stools. The egg is oval with an irregular surface
migrate through the gut wall into the bloodstream and then
(see Figures 56–3C and 56–7). Occasionally, the patient
to the lungs. They enter the alveoli, pass up the bronchi and
trachea, and are swallowed. Within the small intestine, they
become adults (Figures 56–2C and 56–8). They live in the
lumen, do not attach to the wall, and derive their suste-
Treatment
nance from ingested food. The adults are the largest intes-
Albenazole, mebendazole, and ivermectin are effective.
tinal nematodes, often growing to 25 cm or more. Ascaris
lumbricoides is known as the “giant roundworm.” Thou-
Prevention
sands of eggs are laid daily, are passed in the feces, and
differentiate into embryonated eggs in warm, moist soil
Proper disposal of feces can prevent ascariasis.
(see Figure 56–3C). Ingestion of the embryonated eggs
completes the cycle.
mebooksfree.com mebooksfree.com mebooksfree.com ANCYLOSTOMA & NECATOR mebooksfree.com mebooksfree.com
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Disease
Ancylostoma duodenale (Old World hookworm) and Necator
americanus (New World hookworm) cause hookworm
infection.

Important Properties

The life cycle of the hookworms is shown in Figure 56–9.
Humans are infected when filariform larvae in moist soil
penetrate the skin, usually of the feet or legs (Figures
56–2E and 56–10). They are carried by the blood to the
lungs, migrate into the alveoli and up the bronchi and tra-
mebooksfree.com mebooksfree.com mebooksfree.com and G, and 56–11). They feed on blood from the capillaries mebooksfree.com
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chea, and then are swallowed. They develop into adults in
the small intestine, attaching to the wall with either cutting
plates (Necator) or teeth (Ancylostoma) (Figures 56–2D, F,
FIGURE 56–5
Trichuris trichiura—egg. Long arrow points to an
of the intestinal villi. Thousands of eggs per day are passed
egg of T. trichiura. Short arrow points to one of the two “plugs” on
in the feces (Figures 56–3D and 56–12). Eggs develop first
each end of the egg. (Source: Public Dr. M. Melvin, Health Image Library,
into noninfectious, feeding (rhabditiform) larvae and then
Centers for Disease Control and Prevention.)

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