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Paragonimiasis
is infection by the oriental lung fluke Paragonimus westermani
or by one of several other species of Paragonimus.
Image
These are
the only helminthic parasites of humans that, as adult worms,
naturally infect the lungs.
Paragonimiasis occurs in Asia, Africa, and South America.
Human hosts acquire the infection by
eating raw infected crustaceans.
Paragonimus
eggs are coughed up from the lungs, swallowed and passed in the stool.
Miracidia emerge in water and infect a molluscan intermediate host,
after which a sporocyst and a generation of redia develop in the
mollusk.
Infective cercariae emerge and penetrate the gills of a
crustacean. The larvae migrate to soft tissue and encyst.
After a human host ingests the cyst a metacercaria emerges and penetrates the
wall of the stomach, migrates to the diaphragm, bores through the
pleura, and settles in the lung, where it matures into an adult worm,
which survives for 20 years.
The clinical
onset of pulmonary paragonimiasis is insidious, with a diagnostic
triad of cough, hemoptysis, and eggs in the sputa or stool.
Night
sweats, severe chest pain, and pleural effusions are common.
Roentgenograms reveal transient diffuse pulmonary infiltrates.
Although
the adult worms cause pulmonary disease, the larvae occasionally
produce lesions at ectopic sites, such as the brain
(Image Link -multiple areas of caseous necrosis
in the cortex and white matter of brain), liver, gut,
skeletal muscle, testes, and lymph nodes.
The prognosis in pulmonary paragonimiasis is good, but ectopic lesions of brain are often fatal,
even with aggressive treatment.
The worms provoke leukocytic
infiltrates and later, fibrous encapsulation.
Gravid female worms
begin to lay eggs at about 70 days.
Cavities that form around the eggs
contain worms, eggs and necrotic debris.
When these cavities
perforate into a bronchiole or bronchus, the eggs are coughed up or
become lodged in the lung and provoke fibrosis.
Pulmonary paragonimiasis is frequently misdiagnosed as
tuberculosis
.
(Image
Link
-multiple granulomas with fibrosis around the eggs).
Eggs in
sputa or stools provide the definitive diagnosis.
In pleural paragonimiasis, the pleura must be aspirated to obtain eggs.
Praziquantel, the drug of choice, is effective against pulmonary
paragonimiasis.
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