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Pulmonary
Dirofilariasis:
The filarial nematode Dirofilaria
immitis, a common parasite of dogs and other mammals, is transmitted
by mosquitoes.
In humans the infective stage
usually does not reach maturity, but is swept by the venous
circulation into the lung, where it obstructs a pulmonary arteriole
and causes a subpleural infarct, which resolves as a granuloma.
Visit:
Filariasis
;
Onchocerciasis
Originally reported from Japan and Australia, pulmonary dirofilariasis
is most common in the southern and eastern United States.
Most of these
lesions are silent and are discovered as spherical, 1cm to 3cm, subpleural “coin lesions” during radiologic examination of the chest.
Microscopically, a central area of coagulation necrosis is surrounded
by a zone of granulomatous reaction.
The coiled immature and
degenerating D. immitis is located in an arteriole in the
central zone of necrosis.
Lesion may be
resected using video-assisted thoracic surgery (VATS) which appear to
be the best method for diagnosing pulmonary dirofilariasis.
Subcutaneous
Dirofilariasis:
D.tenuis, a
subcutaneous parasite of the racoon, and D. repens, a subcutaneous
parasite of dogs and cats in Europe, Africa, and Asia, cause
subcutaneous dirofilariasis in humans.
Each of these
species is probably transmitted to humans by mosquitoes.
Before reaching
maturity, the infective stage of the worm degenerates and provokes an
abscess, usually surrounded by a granulomatous perimeter.
The most common
site is the subcutaneous tissue of the trunk, but the conjunctiva,
eyelid, scrotum, and breast can also be affected.
Clinically, a
subcutaneous tender nodule gradually enlarges for several weeks.
Microscopically,
a central abscess contains a single coiled worm.
Older lesions are
granulomatous.
The diagnosis is
made by identifying the worm in a biopsy.
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