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Histoplasmosis

Introduction

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, 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 (thanks to www.scielo.br for images), which can get ulcerated and in the gastrointestinal tract that lead to further weakening of the immune system ; this 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.

 Histoplasmosis (Biopsy Shows Granulomatous Reaction With Intracellular Fungus)

Histoplasmosis (Biopsy Shows Granulomatous Reaction With Intracellular Fungus)

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.

 

References

1.The Merck Manual, 7th edition, by M. H. Beer s et al., Whitehouse Station, N.J., 1999. Chapter 158.

2.The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 113.

3. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 164.

4.David Heymann, MD, Editor: Control of Communicable Diseases Manual, 18th Edition, 2004, American Public Health Association.

Last modified: November 9, 2014

Disclaimer
This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.