Histoplasmosis overview: Difference between revisions
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There is no standard screening recommended for histoplasma infection. | |||
==Risk Factors== | ==Risk Factors== | ||
Revision as of 13:26, 4 May 2017
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Prince Tano Djan, BSc, MBChB [2]
Overview
Historical perspective
Histoplasma capsulatum was first described by Samuel Taylor Darling in 1906, who coined the term to describe the "plasmodium-like" organisms in the histocytes. In 1912, Henrique da Rocha-Lima, a Brazilian tropical disease specialist, reported findings from a comparison between Leishmania and Histoplasma and concluded that Histoplasma more closely resembled a yeast than a protozoan. In the late 1940s, William A. DeMonbreun, the first person to culture the organism, suggested that the disease may be prevalent in the United States, not only the tropics, due to mild and carrier forms.
Classification
Histoplasmosis can be classified with respect to the involved organ system. This can include pulmonary, nervous system, cardiovascular system and mediastinum. Histoplasmosis can also be classified according to the severity in to mild, moderate and severe, according to disease duration into acute, subacute, chronic and recurrent and according to the progression of the disease into localized or disseminated histoplasmosis.
Pathophysiology
Histoplasmosis is typically acquired via inhalation of airborne microconidia, often after disturbance of contaminated material in the soil. In majority of the patients the infection is asymtomatic and resolves with host's immune response. In few patients inhalation of large amount of inoculum can result in an acute pulmonary infection with symptoms resembling pneumonia. In patients with immunosuppression, they are unable to mount an adequate T-cell mediated immune response resulting in uncontrolled growth of the organism with spread to the surrounding tissue and increasing the morbidity and mortality of the infection.
Causes
Histoplasmosis is caused by Histoplasma capsulatum a fungus commonly found in bird and bat fecal material and is the causative agent of histoplasmosis. It belongs to the recently recognized fungal family Ajellomycetaceae. It is dimorphic and switches from a mold-like (filamentous) growth form in the natural habitat to a small budding yeast form in the warm-blooded animal host. It is most prevalent in the Ohio and Mississippi River valleys.
Differentiating Histoplasmosis from other Conditions
Epidemiology and Demographics
The incidence of histoplasmosis is estimated by the Centers of Disease Control to be around 500,000 every year in the United States. In the United States, an estimated 60% to 90% of people who live in areas surrounding the Ohio and Mississippi River valleys (where Histoplasma is common in the environment) have been exposed to the fungus at some point during their lifetime.
Screening
There is no standard screening recommended for histoplasma infection.
Risk Factors
Risk factors for histoplasmosis infection include living in or traveling to the Central or Eastern United States. Patients with immunosupression, hematological malignancies, immunosuppresive therapy and infants are at a higher risk of developing disseminated histoplasmosis infection.
Natural History, Complications and Prognosis
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
There are no specific laboratory findings associated with acute histoplasma infection. Diagnosis is confirmed by the demonstration of the yeast cells from tissue samples or body fluids, culture and antigen detection.
Ultrasound
CT
Treatment
Medical therapy
Mild to moderate cases of acute pulmonary histoplasmosis will often resolve without treatment; however, treatment is indicated for moderate to severe acute pulmonary, chronic pulmonary, disseminated, and central nervous system (CNS) histoplasmosis. Typical treatment of severe disease first involves treatment with amphotericin B, followed by oral itraconazole. In many milder cases, simply itraconazole is sufficient. Asymptomatic disease is typically not treated. Past infection results in partial protection against ill effects if reinfected.
Surgical therapy
Prevention
Primary Prevention
Avoid areas that may harbor the fungus, e.g., accumulations of bird or bat droppings. Before starting a job or activity having a risk for exposure to H. capsulatum, consult the NIOSH/NCID Document Histoplasmosis: Protecting Workers at Risk. This document contains information on work practices and personal protective equipment that will reduce the risk of infection.