Current and New Perspectives in the Diagnosis of Blastomycosis and Histoplasmosis

Abstract

The diagnosis of blastomycosis and histoplasmosis can be difficult for clinicians who rarely see infections caused by these environmentally restricted dimorphic fungi. Historically, the diagnosis of blastomycosis has been established by culture and sometimes by histopathologic identification. Currently, antigen detection in urine and serum has been shown to aid in the rapid diagnosis of blastomycosis, and newer antibody assays are likely to contribute to our diagnostic capability in the near future. The gold standard for the diagnosis of histoplasmosis has been culture of the organism from involved tissues, aided in some patients by histopathological verification of the typical yeast forms in tissues. Antigen detection has contributed greatly to the ability of clinicians to rapidly establish the diagnosis of histoplasmosis, especially in severely ill and immunocompromised patients, and antibody testing for Histoplasma capsulatum provides important adjunctive diagnostic capability for several forms of both acute and chronic histoplasmosis. For both of these endemic mycoses, novel molecular tests are under active investigation, but remain available in only a few reference laboratories. In this review, we provide a synopsis of diagnostic test options that aid in establishing whether a patient has blastomycosis or histoplasmosis.

Paediatric Histoplasmosis 2000–2019: A Review of 83 Cases

“…Histoplasma antibody testing and antigen testing were performed to make a diagnosis in 47.4% and 44.9% of children, respectively. For the antibody testing, standard assays employing either complement fixation or immunodiffusion are available, with a reported sensitivity as high as 90% [109]. Paediatric-specific data about the performance of these assays are scarce, but two paediatric single-centre studies do suggest that a high percentage of children with histoplasmosis test antibody positive [82,84].…”

“…The same holds true for antigen testing, which has been used most commonly on urine samples with reported sensitivities between 76 and 90%. Sensitivity is lower when serum samples are used, with some good experiences reported using CSF and bronchoalveolar lavage samples aiding in the diagnostic process [109].…”

Occupational Histoplasmosis: Epidemiology and Prevention Measures

“…Because work-related exposure to Histoplasma often occurs during disruption of bird or bat droppings [ 2 ], following the hierarchy of controls, the best way to prevent exposure to Histoplasma is to prevent the accumulation of bird or bat droppings in the first place. There are recommended protocols for excluding bats and birds from buildings [ 64 , 65 , 66 ].…”

“…capsulatum and H. capsulatum var. duboisii [ 2 , 3 ]. H. capsulatum belongs to the family, Ajellomycetaceae (order Onygenales), that include a unique group of pathogenic fungi that produce a thermally dimorphic yeast phase [ 4 ].…”

“…In the environment, H. capsulatum grows as a saprobic filamentous form and is composed of septate hyphae [ 5 ]. H. capsulatum produces two types of asexual conidia [ 6 ]; tuberculate macroconidia (8–15 µm) and microconidia (2–4 µm) [ 2 , 7 ]. Although there are reported differences between H. capsulatum strains, microconidia are the main conidia produced on the hyphae [ 7 ].…”