Histoplasmosis
duboisii is a pulmonary disease which commonly affects bones
and skin.
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Histoplasmosis
It is caused by the large-celled form or duboisii
variety of Histoplasma capsulatum.
When grown in vitro, mycelial and yeast forms of this fungus are indistinguishable from
those of the classical, small-celled form or capsulatum variety of
this species.
The two can be distinguished from each other only when
the size of the yeastlike cells that develop in tissue is observed.
Diseases caused by the two varieties of Histoplasma capsulatum
are clinically and pathologically distinct.
Natural infection caused by H. capsulatum var. duboisii
has been reported mostly in human and nonhuman primates from Africa.
It is
an important deep mycosis endemic in Central and West Africa and in
the island of Madagascar.
The disease is rarely seen in the United States in persons who
previously lived or travelled in Africa.
Clinically, patients usually present with one or more of the
following: lymphadenopathy ; mucocutaneous lesions characterized by abscess
formation and ulceration ; and insidious osteolytic lesions, particularly in the
ribs, long bones, and cranium. Disseminated disease may also involve
the lungs, liver, spleen, and intestine.
Amphotericin B and excision
of isolated skin lesions are treatment of choice for disseminated and
localized infections, respectively.
Lesions
typically contain a dispersed granulomatous inflammatory reaction in
which large numbers of yeast-like cells are seen within the cytoplasm
of histiocytes and huge multinucleated giant cells.
The spherical to
oval fungal cells are uninucleate and 8 to 15 micro meter in diameter,
have thick walls, and bud by a relatively narrow base.
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Classical "hourglass" and "double-cell"
forms are created when budding daughter cells enlarge until they equal
the size of the parent cells, to which
they remain connected by a narrow base.
Tissue forms of H.
capsulatum var. duboisii and
Blastomyces dermatitidis are
of similar size and shape and thus may be mistaken for each other.
However, the latter buds by a broader base and is multinucleated.
Histoplasmosis capsulati also occurs in Africa,
but its causative agent is much smaller (2 to 4 micrometer) in tissue
than the large-celled duboisii variety.
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