HistoplasmosisIntroduction:
This is a fungal infection, which affects primarily the lungs,
but has become common as progressive disseminated histoplasmosis, particularly
in AIDS patients. It used to be rare in the past decades, but as AIDS has become
more common, so has histoplasmosis. It is transmitted by Histoplasma
capsulatum, which grows in soil as a mold. Dust or soil contaminated
with bird or bat droppings is a particularly good breeding ground for Histoplasma
capsulatum. The geographic distribution is similar to blastomycosis as
is the growth pattern in soil and the mechanism of changeover from spore to hyphen
form inside the lungs, triggered by the rise in temperature from room to body
temperature. If the disease is confined to the lungs, it is a self limiting disease,
which often will heal spontaneously, even without antifungal medications. On the
other hand, if the progressive disseminated form is developing, the mortality
rate without treatment would be in excess of 90%! It is therefore important to
diagnose the condition when the outlook is still good and treat it aggressively,
if there are signs that it it getting progressive.
Signs and Symptoms: Primary histoplasmosis
in the lungs is mostly asymptomatic. There might be cold like symptoms, but as
it is mostly self limiting like most viruses, it can easily be brushed off when
the patient has recovered. Other patients may develop a fever, cough, fatigue
and sometimes pneumonia. If the immune system, particularly the cellular immunity,
is weak as it is in AIDS patients or patients with chronic conditions (see under
"introduction"in
the beginning of this chapter for such conditions), then more symptoms can occur.
This is when progressive disseminated histoplasmosis
should be suspected. The pathogen is now spread from the lungs via the blood stream
into vital organs. This only occurs when the cellular immune system is severely
weakened due to AIDS, cancer, chemotherapy or other debilitating disease (diabetes,
end stage pulmonary disease, kidney failure etc.). Spleen, lymph glands, kidneys
and bone marrow are infected with the pathogen, which multiplies in the white
blood cells (called monocytes, granulocytes and macrophages) that attempt to fight
the disease, but are overcome by it. Skin lesions can suddenly occur, lesions
in the oral cavity (which can get ulcerated) and in the gastrointestinal
tract that lead to further weakening of the immune system and may cause internal
bacterial superinfection and subsequent sepsis. Patients are fatigued, in HIV
patients their overall condition may be worsening, but histoplasmosis, unless
thought of, might be overlooked. It is when suddenly acute emergencies occur
that it becomes apparent that this condition is present such as acute blindness
on one eye from histoplasma infection of the eye socket, which got there via the
blood stream. Or there might be a sudden worsening of the previously low grade
lung infection as a cough is suddenly worsening and x-rays show a chronic
cavitary histoplasmosis, which resembles tuberculosis, but bronchoscopy by
a respirologist proves the diagnosis on biopsy. Other complications are liver
involvement where an inflammatory reactions leads to granulomas. Most of the time
these will heal with calcifications that can be seen on imaging tests. Finally,
in late progressive isseminated histoplasmosis there can be pleural effusions
in the lung cavities, which were caused by spread via the blood stream. Diagnostic
tests: Various body fluids (serum, urine, secretions from phlegm)
and biopsy materials(bone marrow, liver, oral ulcerations) can be sent for cultures.
Histopathology studies using special fungal stains can also help directly identify
Histoplasma capsulatum. For research purposes there is an antigen test available,
but this is not readily available in your neighborhood lab.
Treatment: The
primary lung form of histoplasmosis can be observed by the physician without treatment
to see whether it resolves spontaneously. However, if it is apparent that it turns
chronic and is still localized, it is wiser to treat it and eradicate it, particularly,
if it is in a patient with a known chronic underlying condition that weakens the
immune system. Mild disease is then treated with itraconazole (brand name: Sporanox).
More serious disease such as cavitary histoplasmosis has to be treated with amphotericin
B intravenously. This is also the treatment of choice for severe disseminated
histoplasmosis (Ref. 1, p. 1214). In AIDS patients itraconazole has to be given
indefinitely for prevention of a relapse. If this is not tolerated, intermittent
intravenous therapy with amphotericin B is given instead. |
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