Histoplasma capsulatum and Histoplasmosis: Current Concept for the Diagnosis

Abstract

Histoplasmosis is a global deep mycosis caused by Histoplasma capsulatum (Hc), a dimorphic fungus. It exists on two main varieties Hc capsulatum and Hc duboisii that could be distinguished by their epidemiology, their clinical presentation, and the morphological aspect of the fungus at direct examination of the sample. Laboratory diagnosis of Hc remains a real challenge as it required experience and equipment. Through a general review of literature, the different diagnosis tools for Histoplasma sp. are analyzed, and strengths and weaknesses are pointed according to the context-based value. Isolation of Hc on culture is the gold standard for diagnosis of histoplasmosis. However, it remains less sensitive (sensitivity: up to 77%) and implies long time to result, which can be inappropriate or in adapted for an emergency diagnosis. So, nonculture methods as antigen testing, serology, and molecular biology become available and allow a rapid diagnosis. However, the optimal diagnostic method depends on many parameters as the very wide range of symptomatology, the immune status. Indeed, Ag detection is the best diagnosis tool for PHD (sensitivity: 92-95%) and SCN histoplasmosis (sensitivity: 66%) and serology for the subacute/chronic form (sensitivity: 85-93%). Thus, the clinico-biological dialog is essential, and histoplasmosis management includes an integrated medical approach.

A Case of Histoplasmosis Detected Through Bone Marrow Analysis

“…2,9 To laboratory diagnose of Histoplasmosis, there are several methods such as direct examination for mycology, histopathology, culture, and serology, depending on the laboratory capabilities. 5 The gold standard for the laboratory diagnosis of Histoplasmosis is still culture, however, growth of H. capsulatum is slow and usually takes 2 to 3 weeks or can last up to 8 weeks. 5,6 Therefore, it is necessary to use other methods for faster diagnosis, such as serology or direct examination.…”

“… 5 The gold standard for the laboratory diagnosis of Histoplasmosis is still culture, however, growth of H. capsulatum is slow and usually takes 2 to 3 weeks or can last up to 8 weeks. 5 , 6 Therefore, it is necessary to use other methods for faster diagnosis, such as serology or direct examination. Serology is useful for diagnosis but is not available in many laboratory facilities.…”

“…Histoplasmosis is caused by a dimorphic fungi Histoplasma capsulatum , presenting with a yeast form in body temperature and a hyaline mold form in the natural environment. 5 In the Wright-Giemsa staining, yeasts are round or ellipsoidal shapes, small (2-5 μm in diameter), have a purple nucleus occupied from one-third to one-half of the spore, light green cytoplasm, and surrounded by a clear halo. Most of these yeasts are intracellular (macrophage, histiocyte, neutrophil), and some may be outside macrophages.…”

“…Most of these yeasts are intracellular (macrophage, histiocyte, neutrophil), and some may be outside macrophages. 5 , 10 Types of specimens for this staining method depend on the clinical features of the patient, including bone marrow aspiration, puncture of lymph node, pus or exudates, cerebrospinal fluid, and peripheral blood. Thus, bone marrow analysis also plays an important role in diagnosing Histoplasma capsulatum .…”

“…2,4 To diagnose Histoplasma infection, culture remains the gold standard for laboratory diagnosis but it often takes a long time 2 to 3 weeks or may take up to 8 weeks because of slow growth. 5,6 Therefore, it leads to many cases are reported negative culture results and missed diagnosis because the follow-up period of culture specimen is usually only 1 week. In this issue, some other methods such as serology or bone marrow tests play an important role in rapid identification and early diagnosis, especially in cases of severe disseminated disease.…”