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Histoplasmosis is a disease, usually
affecting the lungs, caused by the
Histoplasma capsulatum fungus. Although
many people that are or have been infected
with H. capsulatum do not appear ill, some
people in the acute phase of the disease
have a dry cough, fever, and chest pains
and do feel ill. There are several types of
histoplasmosis (acute, chronic, and
disseminated, all with subtypes).
H. capsulatum was first described by
Samuel Darling in 1906 within human tissue
cells (histiocytes). In 1932, Katharine Dodd
and Edna Tompkins made the first diagnosis
of histoplasmosis in an infant.
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Types of histoplasmosis:
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Histoplasmosis has three major types of disease, and these
three have other subtypes included in them. They are
summarized with their subtypes as follows:
acute pulmonary histoplasmosis; asymptomatic and
symptomatic;
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chronic pulmonary histoplasmosis; chronic lung symptoms
and occasionally ocular involvement termed ocular
histoplasmosis syndrome; and
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progressive disseminated histoplasmosis: chronic
progressive disseminated histoplasmosis with
oropharyngeal lesions or ulcers; subacute progressive
disseminated histoplasmosis with intestinal, adrenal,
cardiac or central nervous system (CNS) involvement; and
acute progressive disseminated histoplasmosis with
encephalopathy, meningitis, mass lesions and cutaneous
(skin) lesions.
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Causes of histoplasmosis:
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Histoplasmosis is caused by a dimorphic (two forms,
mycelia and yeast) fungus named Histoplasma
capsulatum. The genus name is misleading; the fungus
has no capsule, but early investigators mistakenly
thought it did. The mycelial phase consisting of mycelia
fragments and spores can be inhaled and may reach the
lung alveoli. Macrophages (human phagocytic cells of
the immune system) surround and engulf (phagocytosis)
H. capsulatum, which then changes inside the
macrophages to the yeast form in about 15-18 hours. In
most cases, the macrophage response kills the yeast.
When macrophages fail to kill all the yeast, a variation of
the disease develops because the yeast form multiplies
and invades other cells. The larger the number of
mycelia and spores the person is exposed to, the more
likely the person will develop
symptomatic disease.
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Symptoms and signs of
histoplasmosis:

About 90% of infections caused by H.
capsulatum are asymptomatic (produce no
symptoms). Occasionally, a few asymptomatic
patients will show small scars in lung X-rays.
Symptomatic people often develop fever,
chills, dry cough, malaise, sweats, and
abdominal pains about three to 14 days after
exposure. If the disease progresses,
symptoms such as weight loss, fatigue,
dyspnea, chest pain, and reduced or loss of
vision may occur. A sign of progression are
patchy infiltrates seen on chest X-rays, usually
in the lower lung fields. Other symptoms that
can occur, especially in patients that are
immunosuppressed, are mouth ulcers, fevers,
headaches, confusion, seizures,
encephalopathy, and infrequently, death.
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Treatment of histoplasmosis:
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For asymptomatic people or people with acute localized
infection who are otherwise healthy, antifungal treatment is
usually not recommended as these people have or will
resolve the infection in about three weeks. If symptoms
persist a month or more, itraconazole (Sporanox),
ketoconazole (Nizoral) or amphotericin B (Fungizone,
Amphocin) may be effective. If CNS involvement occurs, or
if the person is compromised by other diseases or is
immunocompromised and has severe histoplasmosis
(progressive disseminated histoplasmosis), either
itraconazole or amphotericin B is recommended. The
lengths of time, dosing amounts, and dosing routes are
usually individualized for the patient; consultations with both
infectious disease and pulmonary specialists are
recommended. Other new azoles compound drugs may be
effective in some difficult or unresponsive cases; the
consultants could help select the appropriate new drug
treatment.
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Prevention of histoplasmosis:
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People living in endemic areas like the Ohio
River Valley are likely to be exposed to
histoplasmosis no matter what they do, since
the fungus is likely in the dust in the air.
However, if they are healthy, most people that
get exposed or infected with H. capsulatum will
be asymptomatic. Immunosuppressed (those
with HIV or cancer or who are receiving
chemotherapy for cancer) might reduce their
chances of exposure if they live in endemic
areas by avoiding high dust areas like
construction sites. Soil can be decontaminated
with 3% formalin under special circumstances.
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