Page 477 - Review of Medical Microbiology and Immunology ( PDFDrive )

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PART VI Parasitology
massive splenomegaly can develop. The most common
cause of death is exsanguination from ruptured esophageal
In some infections, the inflammatory response can cause
varices. Patients infected with S. haematobium have hema-
hyperplasia and fibrosis of the biliary tract, but often there
turia as their chief early complaint. Superimposed bacterial
are no lesions. Clonorchiasis is endemic in China, Japan,
urinary tract infections occur frequently.
Korea, and Indochina, where it affects about 20 million
“Swimmer’s itch,” which consists of pruritic papules, is a
frequent problem in many lakes in the United States. The
from these areas.
papules are an immunologic reaction to the presence in the
skin of the cercariae of nonhuman schistosomes. The pru- people. It is seen in the United States among immigrants
Clinical Findings
ritic papules appear within minutes to hours after expo-
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sure, indicating that this is an immediate (immunoglobulin
Most infections are asymptomatic. In patients with a heavy
worm burden, upper abdominal pain, anorexia, hepato-
[Ig] E–mediated) hypersensitivity. These nonhuman schis-
tosomes are incapable of replicating in humans and do not
cause disseminated disease.
Laboratory Diagnosis
Laboratory Diagnosis
Diagnosis is made by finding the typical small, brownish,
operculated eggs in the stool (see Figure 55–4C). Serologic
Diagnosis depends on finding the characteristic ova in the
tests are not useful.
feces or urine. The large lateral spine of S. mansoni and
the rudimentary spine of S. japonicum are typical, as is the
large terminal spine of S. haematobium (see Figures 55–4A
and B, 55–5, and 55–6). Serologic tests are not useful. Treatment
Praziquantel is an effective drug.
Moderate eosinophilia occurs.
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Prevention
Treatment
disposal of human waste.
Praziquantel is the treatment of choice for all three
species.
PARAGONIMUS
Prevention
Disease
Prevention involves proper disposal of human waste and
Paragonimus westermani, the lung fluke, causes
eradication of the snail host when possible. Swimming in
paragonimiasis.
areas of endemic infection should be avoided.
Important Properties
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CLONORCHIS
mebooksfree.com mebooksfree.com mebooksfree.com cariae). After excystation in the small intestine, immature mebooksfree.com
Humans are infected by eating raw or undercooked crab
Disease
meat (or crayfish) containing the encysted larvae (metacer-
Clonorchis sinensis causes clonorchiasis (Asian liver fluke
flukes penetrate the intestinal wall and migrate through the
infection).
diaphragm into the lung parenchyma. They differentiate
into hermaphroditic adults (see Figure 55–2C) and produce
Important Properties
eggs that enter the bronchioles and are coughed up or swal-
lowed (see Figure 55–4D). Eggs in either sputum or feces
Humans are infected by eating raw or undercooked fish
that reach fresh water hatch into miracidia, which enter
containing the encysted larvae (metacercariae). After
excystation in the duodenum, immature flukes enter the
first into larvae (rediae) and then into many free-swimming
biliary ducts and differentiate into adults (see Figure 55–2B).
cercariae. The cercariae infect and encyst in freshwater
The hermaphroditic adults produce eggs, which are excreted snails (first intermediate hosts). There, they differentiate
crabs (second intermediate hosts). The cycle is completed
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in the feces (see Figure 55–4C). Upon reaching fresh
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when undercooked infected crabs are eaten by humans.
water, the eggs are ingested by snails, which are the first
intermediate hosts. The eggs hatch within the gut and dif-
ferentiate first into larvae (rediae) and then into many free-
swimming cercariae. Cercariae encyst under the scales of
Within the lung, the worms exist in a fibrous capsule that
certain freshwater fish (second intermediate hosts), which
communicates with a bronchiole. Secondary bacterial
are then eaten by humans.
infection frequently occurs, resulting in bloody sputum.
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