Evaluation of cross-reactions in Histoplasma capsulatum serologic tests

Testing for Blastomycosis, Coccidioidomycosis, and Histoplasmosis at a Major Commercial Laboratory, United States, 2019-2024

Background

Blastomycosis, coccidioidomycosis, and histoplasmosis are environmentally acquired fungal diseases that clinically resemble bacterial and viral community-acquired pneumonia and require laboratory testing for diagnosis. Patients frequently present to primary care and experience diagnostic delays when a fungal etiology is not initially suspected. Current national-level public health surveillance for these diseases is limited and does not include laboratory data, so nationwide testing practices are unknown.

Methods

We identified laboratory tests for blastomycosis, coccidioidomycosis, and histoplasmosis ordered during 1 March 2019-29 February 2024 and performed within a major national commercial laboratory system. We analyzed test results, patient and healthcare provider features, reasons for testing, and temporal trends.

Results

Results included 5693 Blastomyces complement fixation tests (of those, 12% were positive), 71 858 immunodiffusion tests (0.1% positive), and 1186 serum enzyme immunoassay (EIA) tests (11% positive); 154 989 Coccidioides EIA immunoglobulin M results (5% positive) and 154 968 immunoglobulin G results (8% positive); and 46 346 Histoplasma complement fixation tests (30% positive), 49 062 immunodiffusion tests (1% positive), 35 506 serum EIA tests (4% positive), and 82 489 urine EIA tests (2% positive). Most histoplasmosis (58%-74%) and blastomycosis (42%-68%) tests were ordered from hospitals, whereas coccidioidomycosis tests were most frequently ordered by primary care providers (40%). A yearly average of 2727 positive tests were ordered by healthcare providers in states without public health surveillance for these diseases.

Conclusions

Blastomycosis, coccidioidomycosis, and histoplasmosis are likely underdetected in primary care settings or by public health surveillance. Increased testing by primary care providers and expanded surveillance are needed to reduce disease burden.

Prevalence of Histoplasma Antigenuria among Outpatient Cohort with Advanced HIV in Kampala, Uganda

In sub-Saharan Africa, an estimated 25% of people with HIV present with advanced HIV and are at high risk of opportunistic infections. Whereas histoplasmosis has occasionally been seen in Uganda, the understanding of the local risk of acute infection is limited. We sought to determine the prevalence of Histoplasma antigenuria using an enzyme immunoassay (EIA, clarus Histoplasma GM EIA, IMMY; Norman, OK, USA) in a cohort of outpatients with advanced HIV disease in Kampala, Uganda. Among the persons with positive urine Histoplasma antigen tests, we assessed their clinical presentation and outcomes. The EIA was run on stored urine samples as per the manufacturer's instructions. Specimens ≥1 EIA units were considered positive. Among the 388 tested urine samples, 4 (1.2%) were positive for Histoplasma antigen. The histoplasmosis prevalence among participants with a CD4 < 100 cells/mcL was 2.5% (4/158). Three of the four participants with a positive Histoplasma antigen test reported systemic symptoms consistent with histoplasmosis. All four participants had a positive urine lipoarabinomannan test and were treated for tuberculosis. By the four-week follow-up visit, all participants were clinically improved, alive, and in care without antifungal therapy. In advanced HIV, the clinical presentations of tuberculosis and histoplasmosis overlap. The value of histoplasmosis screening and pre-emptive treatment is an area of future research.

A multicentre external quality assessment: A first step to standardise PCR protocols for the diagnosis of histoplasmosis and coccidioidomycosis

BACKGROUND

In-house real-time PCR (qPCR) is increasingly used to diagnose the so-called endemic mycoses as commercial assays are not widely available.

OBJECTIVES

To compare the performance of different molecular diagnostic assays for detecting Histoplasma capsulatum and Coccidioides spp. in five European reference laboratories.

METHODS

Two blinded external quality assessment (EQA) panels were sent to each laboratory that performed the analysis with their in-house assays. Both panels included a range of concentrations of H. capsulatum (n = 7) and Coccidioides spp. (n = 6), negative control and DNA from other fungi. Four laboratories used specific qPCRs, and one laboratory a broad-range fungal conventional PCR (cPCR) and a specific cPCR for H. capsulatum with subsequent sequencing.

RESULTS

qPCR assays were the most sensitive for the detection of H. capsulatum DNA. The lowest amount of H. capsulatum DNA detected was 1-4 fg, 0.1 pg and 10 pg for qPCRs, specific cPCR and broad-range cPCR, respectively. False positive results occurred with high concentrations of Blastomyces dermatitidis DNA in two laboratories and with Emergomyces spp. in one laboratory. For the Coccidioides panel, the lowest amount of DNA detected was 1-16 fg by qPCRs and 10 pg with the broad-range cPCR. One laboratory reported a false positive result by qPCR with high load of Uncinocarpus DNA.

CONCLUSION

All five laboratories were able to correctly detect H. capsulatum and Coccidioides spp. DNA and qPCRs had a better performance than specific cPCR and broad-range cPCR. EQAs may help standardise in-house molecular tests for the so-called endemic mycoses improving patient management.

Histoplasma capsulatum Complement Fixation and Immunodiffusion Assay Sensitivity in Culture-Confirmed Cases of Histoplasmosis: a 10-Year Retrospective Review (2011 to 2020)

The detection of antibodies against Histoplasma capsulatum remains a frequently relied-on approach to diagnose histoplasmosis. We retrospectively assessed the performances of complement fixation (CF) and immunodiffusion (ID) assays for anti-Histoplasma antibody detection in patients with culture-confirmed histoplasmosis at Mayo Clinic (Rochester, MN) over a 10-year period (2011 to 2020). Among 67 culture-confirmed patients who also had H. capsulatum CF/ID testing ordered, 51 (67.1%) were immunocompromised, 34 (50.7%) had localized disease, and 51 (76.1%) presented with <3 months of symptoms before testing. H. capsulatum CF and/or ID testing was positive in 47 (70.1%) patients, with both assays being positive in 39 cases. CF was positive in 44 (65.7%) patients, with reactivity against both H. capsulatum mycelial and yeast antigens in 30 (68.2%) cases, whereas 11 (25%) and 3 (6.8%) individuals had antibodies to the CF yeast or mycelial antigen only, respectively. H. capsulatum ID was positive in 42 (62.7%) patients, with the presence of the M-band only or the H- and M-bands in 27 (64.3%) and 15 (35.7%) cases, respectively. Among 18 serially tested patients, 12 remained ID and/or CF positive at the final time point (median, 154 days; range, 20 to 480 days). Serial CF testing showed that antibodies to the mycelial antigen serorevert to negative more frequently (6/11) than antibodies to the yeast antigen (2/13). There was no statistically significant difference in antibody positivity relative to patient immune status, degree of disease dissemination, or symptom duration. Serologic testing remains a valuable asset to support the diagnosis of histoplasmosis, particularly when direct detection methods fail to identify an infection.

Immunologic Diagnosis of Endemic Mycoses

The endemic mycoses blastomycosis, coccidioidomycosis, histoplasmosis, paracoccidioidomycosis, cryptococcosis, sporotrichosis, talaromycosis, adiaspiromycosis, and emergomycosis are mostly caused by geographically limited thermally dimorphic fungi (except for cryptococcosis), and their diagnoses can be challenging. Usual laboratory methods involved in endemic mycoses diagnosis include microscopic examination and culture of biological samples; however, serologic, histopathologic, and molecular techniques have been implemented in the last few years for the diagnosis of these mycoses since the recovery and identification of their etiologic agents is time-consuming and lacks in sensitivity. In this review, we focus on the immunologic diagnostic methods related to antibody and antigen detection since their evidence is presumptive diagnosis, and in some mycoses, such as cryptococcosis, it is definitive diagnosis.

Histoplasmosis

Histoplasmosis is one of the commonest endemic mycoses in the Americas yet is often underdiagnosed and neglected as a public health priority. This review outlines the evolving understanding of its epidemiology and the clinical syndromes of histoplasmosis, in addition to up-to-date diagnostic and treatment guidelines. A focus on histoplasmosis in advanced HIV is included. The challenges pertinent to histoplasmosis management in Latin America, with recommendations made through international expert consensus are discussed.

Diagnostic Aspects of Chronic Pulmonary Aspergillosis: Present and New Directions

Purpose of Review

Diagnosis of chronic pulmonary aspergillosis (CPA) is important since many diseases have a similar appearance, but require different treatment. This review presents the well-established diagnostic criteria and new laboratory diagnostic approaches that have been evaluated for the diagnosis of this condition.

Recent Findings

Respiratory fungal culture is insensitive for CPA diagnosis. There are many new tests available, especially new platforms to detectAspergillusIgG. The most recent innovation is a lateral flow device, a point-of-care test that can be used in resource-constrained settings. Chest radiographs without cavitation or pleural thickening have a 100% negative predictive value for chronic cavitary pulmonary aspergillosis in the African setting.

Summary

Early diagnosis of CPA is important to avoid inappropriate treatment. It is our contention that these new diagnostics will transform the diagnosis of CPA and reduce the number of undiagnosed cases or cases with a late diagnosis.

Talaromyces marneffei laboratory cross reactivity with Histoplasma and Blastomyces urinary antigen

Talaromyces marneffei is a fungal opportunistic infection usually seen in immunocompromised patients from eastern countries. In the US when examining HIV-patients for suspected fungal infections, laboratory serological tests guide therapy until cultures are available. We present the case of a 35-year-old HIV patient originally from Thailand in which urine lab results were positive for Blastomyces and Histoplasma antigen, but biopsy showed T. marneffei. Concomitantly the patient presented with hyponatremia which was deemed to be from SIADH. We present the first case of a patient with T. marneffei cross reactivity with Blastomyces, Histoplasma and SIADH due to pulmonary disease.

Enhanced Surveillance for Coccidioidomycosis, 14 US States, 2016

Although coccidioidomycosis in Arizona and California has been well-characterized, much remains unknown about its epidemiology in states where it is not highly endemic. We conducted enhanced surveillance in 14 such states in 2016 by identifying cases according to the Council of State and Territorial Epidemiologists case definition and interviewing patients about their demographic characteristics, clinical features, and exposures. Among 186 patients, median time from seeking healthcare to diagnosis was 38 days (range 1–1,654 days); 70% had another condition diagnosed before coccidioidomycosis testing occurred (of whom 83% were prescribed antibacterial medications); 43% were hospitalized; and 29% had culture-positive coccidioidomycosis. Most (83%) patients from nonendemic states had traveled to a coccidioidomycosis-endemic area. Coccidioidomycosis can cause severe disease in residents of non–highly endemic states, a finding consistent with previous studies in Arizona, and less severe cases likely go undiagnosed or unreported. Improved coccidioidomycosis awareness in non–highly endemic areas is needed.

Serological Evidence of Infection by Paracoccidioides brasiliensis in Dogs with Leishmaniasis

Paracoccidioidomycosis is a systemic mycosis prevalent in Latin American countries, caused by the dimorphic fungi Paracoccidioides brasiliensis and P. lutzii. The habitat of these fungi in nature remains undefined, although it is believed that infection occurs by inhalation of infective propagules present in soil. Sentinel animals, such as dogs, can be valuable epidemiological markers of paracoccidioidomycosis. Taking into account that paracoccidioidomycosis and visceral leishmaniasis may occur in the same area, the objective of this study was to evaluate the occurrence of P. brasiliensis infection in dogs positive for Leishmania sp. Serum samples of dogs positive (n = 199) and negative (n = 101) for Leishmania sp. were analyzed by the immunodiffusion test using P. brasiliensis exoantigen, and 22 samples (7.3%) were positive. The serum samples positive in the immunodiffusion test were also analyzed by Western blotting using the P. brasiliensis gp43 recombinant protein, and 86% of the samples were positive. A high positive correlation (r = 0.96) between positivity for Leishmania sp. and P. brasiliensis was observed. These data suggest an association between leishmaniasis and paracoccidioidomycosis in dogs.

Laboratory Diagnostics for Histoplasmosis

The diagnosis of histoplasmosis is based on a multifaceted approach that includes clinical, radiographic, and laboratory evidence of disease. The gold standards for laboratory diagnosis include demonstration of yeast on pathological examination of tissue and isolation of the mold in the culture of clinical specimens; however, antigen detection has provided a rapid, noninvasive, and highly sensitive method for diagnosis and is a useful marker of treatment response. Molecular methods with improved sensitivity on clinical specimens are being developed but are not yet ready for widespread clinical use. This review synthesizes currently available laboratory diagnostics for histoplasmosis, with an emphasis on complexities of testing and performance in various clinical contexts.

Diagnostic Methods for Histoplasmosis: Focus on Endemic Countries with Variable Infrastructure Levels

Diagnosis of histoplasmosis remains challenging in resource-limited regions where HIV/AIDS is epidemic and histoplasmosis is endemic. Early and rapid detection of histoplasmosis is essential to preventing morbidity and mortality, yet few diagnostic options are available in low-resource areas of the world. The aim of this review is to provide an overview of the current status of the diagnosis of histoplasmosis, including an update on recent developments and utilization of new technologies. We discuss the specific diagnostic challenges faced in endemic regions, emphasizing the need for greater availability and standardization of rapid diagnostics for this endemic and neglected disease. While significant progress has been made in the development of new methods, clinical utility must be established by means of formal and extensive clinical studies.

Evaluation of an enzyme-linked immunosorbent assay using purified, deglycosylated histoplasmin for different clinical manifestations of histoplasmosis

Diagnosis of invasive fungal diseases remains problematic, especially in undeveloped countries. We have developed an enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies to Histoplasma capsulatum using metaperiodate treated purified histoplasmin (ptHMIN). Our ELISA was validated comparing sera from patients with histoplasmosis, related mycoses, and healthy individuals. The overall test specificity was 96%, with sensitivities of 100% (8/8) in acute disease, 90% (9/10) in chronic disease, 89% (8/9) in disseminated infection in individuals without HIV infection, 86% (12/14) in disseminated disease in the setting of HIV infection and 100% (3/3) in mediastinal histoplasmosis. These parameters are superior to the use of untreated histoplasmin in diagnostic ELISAs. The high specificities, sensitivities, and simplicity of our ELISA support further development of a deglycosylated HMIN ELISA for clinical use and for monitoring the humoral immune response during therapy in patients with chronic and disseminated histoplasmosis.

Histoplasmosis in children

Histoplamosis is the most common primary systemic mycosis in the USA and is becoming more common as an opportunistic infection in HIV patients worldwide. In children the rate of asymptomatic infection is high. However, in infants with an immature immunological system, disseminated disease may occur. The clinical picture is variable depending on the immunological status. At the onset of the infection clinical manifestations are non specific (headache, fever, cough and nausea). Usually, these symptoms are self-limited and improve without treatment. However, patients with disseminated diseases present with prolonged fever, malaise, cough and weight loss. Hepatosplenomegaly is frequent in infants. Chest radiographs may be normal in 40 to 50% of patients with disseminated disease but findings such as lobar or diffuse infiltrates, cavitations, hilar adenopathy, or any combination of these may be found. Frequently, the clinical presentation is misdiagnosed as tuberculosis. Skin tests, serological reaction and specific cultures are used for diagnosis confirmation. Treatment indications and regimens are similar to those for adults, except that amphotericin B deoxycholate is usually well tolerated in children.

Current status and future perspectives on molecular and serological methods in diagnostic mycology

Invasive fungal infections are an important cause of infectious morbidity. Nonculture-based methods are increasingly used for rapid, accurate diagnosis to improve patient outcomes. New and existing DNA amplification platforms have high sensitivity and specificity for direct detection and identification of fungi in clinical specimens. Since laboratories are increasingly reliant on DNA sequencing for fungal identification, measures to improve sequence interpretation should support validation of reference isolates and quality control in public gene repositories. Novel technologies (e.g., isothermal and PNA FISH methods), platforms enabling high-throughput analyses (e.g., DNA microarrays and Luminex® xMAP™) and/or commercial PCR assays warrant further evaluation for routine diagnostic use. Notwithstanding the advantages of molecular tests, serological assays remain clinically useful for patient management. The serum Aspergillus galactomannan test has been incorporated into diagnostic algorithms of invasive aspergillosis. Both the galactomannan and the serum β-D-glucan test have value for diagnosing infection and monitoring therapeutic response.

Guedes HL, Nosanchuk JD, Zancopé-Oliveira RM. Biological function and molecular mapping of M antigen in yeast phase of Histoplasma capsulatum

Histoplasmosis, due to the intracellular fungus Histoplasma capsulatum, can be diagnosed by demonstrating the presence of antibodies specific to the immunodominant M antigen. However, the role of this protein in the pathogenesis of histoplasmosis has not been elucidated. We sought to structurally and immunologically characterize the protein, determine yeast cell surface expression, and confirm catalase activity. A 3D-rendering of the M antigen by homology modeling revealed that the structures and domains closely resemble characterized fungal catalases. We generated monoclonal antibodies (mAbs) to the protein and determined that the M antigen is present on the yeast cell surface and in cell wall/cell membrane preparations. Similarly, we found that the majority of catalase activity was in extracts containing fungal surface antigens and that the M antigen is not significantly secreted by live yeast cells. The mAbs also identified unique epitopes on the M antigen. The localization of the M antigen to the cell surface of H. capsulatum yeast and the characterization of the protein's major epitopes have important implications since it demonstrates that although the protein may participate in protecting the fungus against oxidative stress it is also accessible to host immune cells and antibody.

Isoelectric focusing and ELISA evaluation of a Blastomyces dermatitidis human isolate

Blastomyces dermatitidis is a dimorphic fungal organism and the causative agent of blastomycosis. This organism is endemic east of the Mississippi river as is the fungal organism Histoplasma capsulatum. This study was performed to determine if sensitive and specific antigens from the B. dermatitidis yeast phase lysate (human isolate 592) could be separated using isoelectric focusing (IEF) to eliminate antigens that are cross-reactive with H. capsulatum. Indirect enzyme linked immunosorbent assays were performed to test for reactivity and cross-reactivity and indicate that certain fractions (4-6) were highly reactive. Fraction 16 exhibited a high degree of cross-reactivity with H. capsulatum. This study indicates that IEF may be a useful method for the separation of B. dermatitidis proteins.

Production and evaluation of reagents for detection of Histoplasma capsulatum antigenuria by enzyme immunoassay

The detection of urinary Histoplasma capsulatum polysaccharide antigen (HPA) by enzyme immunoassay (EIA) has proven useful for the presumptive diagnosis of histoplasmosis in AIDS patients. Assay limitations include (i) detection of a largely uncharacterized antigen and (ii) difficulty in reproducibly generating antibodies for use in the EIA. To improve antibody production for use in this test and to better understand the antigen being detected, we compared rabbit antibodies elicited using various immunization schedules, routes, and H. capsulatum-derived antigens. Antibodies were evaluated by EIA for their ability to detect purified H. capsulatum C antigen (C-Ag) and antigenuria. Reported as enzyme immunoassay (EI) units (the A(450) with antigen divided by the A(450) without antigen), results demonstrated that intravenous immunization of rabbits with whole, killed yeast-phase cells (yeast-i.v. regimen) produced antibodies giving the highest EI values in the C-Ag EIA (mean EI units +/- standard deviation, 14.9 +/- 0.6 versus 6.4 +/- 0.4 for rabbits immunized with C-Ag versus 2.4 +/- 0.3 for all other regimens combined). Yeast-i.v. antibodies were highly sensitive for the detection of antigenuria in patients with histoplasmosis, as shown by the following results: 12/12 patients compared to 10/12, 6/12, 3/12, and 3/12, respectively, for antibodies from rabbits immunized with (i) C-Ag; (ii) whole, killed yeast-phase cells administered subcutaneously and intramuscularly; (iii) yeast-phase culture filtrates; and (iv) HPA-positive urine. Rabbits immunized using the yeast-i.v. regimen also gave higher peak antibody titers than rabbits immunized by any other regimen (P < 0.03), and their antibodies were most comparable in reactivity to antibodies produced for use in the standard HPA-EIA test (P < 0.001). Therefore, rabbits immunized using the yeast-i.v. regimen produced the most sensitive antibodies with the highest titers for detection of C-Ag and antigenuria in histoplasmosis patients.

Use of mycelial-phase Sporothrix schenckii exoantigens in an enzyme-linked immunosorbent assay for diagnosis of sporotrichosis by antibody detection

An enzyme-linked immunosorbent assay (ELISA) was developed for specific antibody detection in serum specimens of patients with sporotrichosis. The assay was made with mycelial-phase Sporothrix schenckii exoantigens and was tested against 90 sera from patients with different clinical forms of sporotrichosis. Potential cross-reactions were analyzed with 72 heterologous sera from patients with paracoccidioidomycosis, cryptococcosis, aspergillosis, histoplasmosis, tuberculosis, and American tegumentary leishmaniasis, as well as 76 sera from healthy controls. We found a sensitivity of 97% and a specificity of 89% in this assay. Some cross-reactions were seen, as observed in other immunoassays for the diagnosis of sporotrichosis. The ELISA appears to be especially useful for cutaneous forms of disease, since these are not promptly diagnosed with available immunoprecipitation or agglutination techniques. These results suggest that the ELISA using mycelial-phase S. schenckii exoantigens is a very sensitive diagnostic tool for the serodiagnosis of sporotrichosis and can be used in conjunction with conventional methods of diagnosis, particularly in cases where cross-reactions or false-positive results are experienced with the serodiagnosis.

Histoplasmosis: a clinical and laboratory update

Infection with Histoplasma capsulatum occurs commonly in areas in the Midwestern United States and Central America, but symptomatic disease requiring medical care is manifest in very few patients. The extent of disease depends on the number of conidia inhaled and the function of the host's cellular immune system. Pulmonary infection is the primary manifestation of histoplasmosis, varying from mild pneumonitis to severe acute respiratory distress syndrome. In those with emphysema, a chronic progressive form of histoplasmosis can ensue. Dissemination of H. capsulatum within macrophages is common and becomes symptomatic primarily in patients with defects in cellular immunity. The spectrum of disseminated infection includes acute, severe, life-threatening sepsis and chronic, slowly progressive infection. Diagnostic accuracy has improved greatly with the use of an assay for Histoplasma antigen in the urine; serology remains useful for certain forms of histoplasmosis, and culture is the ultimate confirming diagnostic test. Classically, histoplasmosis has been treated with long courses of amphotericin B. Today, amphotericin B is rarely used except for severe infection and then only for a few weeks, followed by azole therapy. Itraconazole is the azole of choice following initial amphotericin B treatment and for primary treatment of mild to moderate histoplasmosis.

Improvements in diagnosis of histoplasmosis

Understanding the uses and limitations of a battery of laboratory methods is essential to diagnose histoplasmosis. Antigen detection and serology are valuable adjuncts to histopathology and culture. Improvements incorporated into the second-generation Histoplasma antigen assay have increased its sensitivity and specificity for diagnosis of histoplasmosis. More recently, the antigen assay has been modified to provide quantitation, which improves reproducibility and facilitates monitoring antigen clearance during treatment. Furthermore, detection of antigen in bronchoalveolar lavage fluid increases the sensitivity for diagnosis of pulmonary histoplasmosis. Serological tests for antibodies are also useful, but may be falsely negative in immunosuppressed patients. In addition, elevated antibody titres persist for several years following initial infection, complicating their interpretation. Although histopathology may provide for rapid diagnosis, its sensitivity is < 50% in patients with disseminated disease and even lower in pulmonary histoplasmosis. Polymerase chain reaction has been described, but sensitivity is less than that of histopathology. Culture, although highly specific, has notable limitations, including insensitivity, a need for invasive procedures and delayed growth. This review provides the background for understanding the role of a battery of diagnostic methods in histoplasmosis. Tests facilitating a rapid diagnosis are expected to improve the outcome in patients with severe disease.

Evaluation of Serological Diagnosis Tests for Tuberculosis in Hemodialysis Patients

Patients receiving hemodialysis are generally considered to be at increased risk of developing tuberculosis. In the current study, in order to evaluate the usefulness of serological tests in dialysis patients, serum antibodies for tuberculous glycolipids antigen (TBGL) and for lipoarabinomannan (LAM) were measured in hemodialysis patients. The present study included 243 hemodialysis patients. Serum antibodies for TBGL and LAM were measured. Tuberculin skin tests were carried out and chest X-rays evaluated at the same time. There were no patients with active tuberculosis at the time of blood sampling. Thirty-six patients (14.8%) and 25 patients (10.3%) were positive for anti-TBGL antibody and anti-LAM antibody, respectively. One hundred and fifty-five patients (63.8%) were positive for tuberculin skin testing and 123 patients (50.6%) had old pulmonary tuberculosis on their chest X-ray. There was no significant correlation between the results of anti-TBGL antibody and anti-LAM antibody. There were no relationships among the results of tuberculin skin test and the two serological tests. However, positivity of anti-TBGL antibody and anti-LAM antibody was significantly higher in patients with findings of old tuberculosis on the chest X-ray than those without findings. The current results show that these serological tests are positive more frequently in hemodialysis patients without any proof of active tuberculosis than in healthy subjects (2%) and careful interpretation is necessary for relevant results.

DIAGNOSIS OF HISTOPLASMOSIS

Endemic mycoses can be challenging to diagnose and accurate interpretation of laboratory data is important to ensure the most appropriate treatment for the patients. Although the definitive diagnosis of histoplasmosis (HP), one of the most frequent endemic mycoses in the world, is achieved by direct diagnosis performed by micro and/or macroscopic observation of Histoplasma capsulatum (H. capsulatum), serologic evidence of this fungal infection is important since the isolation of the etiologic agents is time-consuming and insensitive. A variety of immunoassays have been used to detect specific antibodies to H. capsulatum. The most applied technique for antibody detection is immunodiffusion with sensitivity between 70 to 100 % and specificity of 100%, depending on the clinical form. The complement fixation (CF) test, a methodology extensively used on the past, is less specific (60 to 90%). Detecting fungal antigens by immunoassays is valuable in immunocompromised individuals where such assays achieve positive predictive values of 96-98%. Most current tests in diagnostic laboratories still utilize unpurified antigenic complexes from either whole fungal cells or their culture filtrates. Emphasis has shifted, however, to clinical immunoassays using highly purified and well-characterized antigens including recombinant antigens. In this paper, we review the current conventional diagnostic tools, such as complement fixation and immunodiffusion, outline the development of novel diagnostic reagents and methods, and discuss their relative merits and disadvantages to the immunodiagnostic of this mycosis.

Diagnosis and Management of Central Nervous System Histoplasmosis

Two cases of Histoplasma meningitis are presented, illustrating the difficulty in diagnosis and treatment. The first case occurred in a patient with acquired immunodeficiency syndrome as a relapse of disseminated histoplasmosis and resolved after prolonged treatment and ongoing antiretroviral therapy. The second case occurred in a cardiac allograft recipient as meningitis and focal brain lesions that responded to liposomal amphotericin B, but the patient died shortly after therapy was completed. Unfortunately, there are no prospective studies addressing the diagnosis and management of patients with histoplasmosis of the central nervous system from which to provide evidence-based guidelines for care. In the absence of such data, an approach will be presented on the basis of our experience and opinions.

Current diagnosis of histoplasmosis

Histoplasmosis is a common infection endemic in many regions of America, Asia, India and Africa, with sporadic cases also occurring throughout the world. Although excellent laboratory methods for diagnosis are available, there are deficiencies that must be met by continued research. Clinicians and laboratory directors must be familiar with the uses and limitations of a battery of serologic and mycological tests to accurately diagnose histoplasmosis. Research is needed to reduce false-negative and false-positive results, and to improve the identification of the organism in tissues. Approaches to the diagnosis of histoplasmosis and areas that require further research will be reviewed.

[Oral histoplasmosis 34 years after return of Africa]

INTRODUCTION

Histoplasmosis is a tropical fungal infection sharing many similarities with tuberculosis: the transmission by air dropplets, the usually asymptomatic primary-infection, the disseminated infection encountered among immunosuppressed patients and the granulomatous pathological lesions. In France, histoplasmosis is uncommon and may be misdiagnosed as tuberculosis.

OBSERVATION

A 78 years old male patient presents with a raspberry-like lesion of the mouth causing difficulties to eat and weight loss of 14 kg. The diagnosis of tuberculosis is evoked because of the presence of a giant-cell granuloma in one of the biopsies. The histoplasmosis serology, requested because the patient stayed in Africa, is positive. Revisions of the pathology put into evidence the presence of spores in histiocytes confirming diagnosis of histoplasmosis. The treatment with itraconazole is effective.

CONCLUSION

Histoplasmosis is a differential diagnosis of tuberculosis, especially in endemic regions. The histoplasmosis serology can be useful. The reference in diagnosis examinations keeps being the microscopic observation of spores and their mycological growth.

Histoplasmosis

The diagnosis of histoplasmosis depends on recognition of the different clinical manifestations of infection, accompanied by knowledge of the accuracy and limitations of tests used for diagnosis of fungal infections. Although most infections are asymptomatic, histoplasmosis can be severe, or even fatal, in patients who have experienced a heavy exposure, have underlying immune defects, or develop progressive disease that is not recognized and treated. This article provides an up-to-date clinical review of histoplasmosis, focusing on recognition, diagnosis, and management.

[Outbreak of histoplasmosis in Pedro Leopoldo, Minas Gerais, Brazil]

An outbreak of histoplasmosis was spotted in Pedro Leopoldo, a city in Minas Gerais State, Brazil, in 1997, where four individuals had been in contact with a bat-inhabited cave. Acute pulmonary histoplasmosis diagnosis was made by the use of clinical, serologic, radiographic and epidemiological criteria. An antifungal treatment with ketoconazole (400mg daily for 30 days) was administered resulting in symptons' remission in a few days.

Gastrointestinal histoplasmosis in patients with AIDS: case report and review

Histoplasmosis is the most common endemic mycosis in individuals with AIDS, occurring in 2%-5% of this population. Infection is more likely to be disseminated than in immunocompetent individuals and generally presents insidiously with nonspecific symptoms. The gastrointestinal tract is involved in 70%-90% of cases of disseminated histoplasmosis, yet gastrointestinal histoplasmosis per se is infrequently encountered in patients with AIDS. The diagnosis of gastrointestinal histoplasmosis is often not suspected, particularly in areas of nonendemicity, and a delay in diagnosis may lead to increased morbidity and risk of death. Since antifungal therapy improves outcome for >80% of AIDS patients with histoplasmosis, it is essential that caregivers be aware of the varied presentations of gastrointestinal histoplasmosis in order to diagnose and to treat this potentially life-threatening infection effectively.

Detection of specific antibodies to an antigenic mannoprotein for diagnosis of Penicillium marneffei penicilliosis

The disseminated and progressive fungal disease Penicillium marneffei penicilliosis is one of the most common infectious diseases in AIDS patients in Southeast Asia. To diagnose systemic penicilliosis, we developed an enzyme-linked immunosorbent assay (ELISA)-based antibody test with Mp1p, a purified recombinant antigenic mannoprotein of P. marneffei. Evaluation of the test with guinea pig sera against P. marneffei and other pathogenic fungi indicated that this assay was specific for P. marneffei. Clinical evaluation revealed that high levels of specific antibody were detected in two immunocompetent penicilliosis patients. Furthermore, approximately 80% (14 of 17) of the documented penicilliosis patients with human immunodeficiency virus tested positive for the specific antibody. No false-positive results were found for serum samples from 90 healthy blood donors, 20 patients with typhoid fever, and 55 patients with tuberculosis, indicating a high specificity of the test. Thus, this ELISA-based test for the detection of anti-Mp1p antibody can be of significant value as a diagnostic for penicilliosis.

Development of a novel antigen detection test for histoplasmosis

Histoplasmosis is an important systemic fungal infection, particularly among immunocompromised individuals living or travelling in areas of endemicity, who, without antifungal therapy, may develop a progressive disseminated fatal infection. For such patients, the detection of antibody responses by immunodiffusion or complement fixation test is of limited use. In contrast, the detection of Histoplasma capsulatum circulating antigens may provide a more practical approach to the rapid diagnosis of the disease. Accordingly, an inhibition enzyme-linked immunosorbent assay (ELISA) for the detection of a 69- to 70-kDa H. capsulatum-specific determinant and incorporating a species-specific murine monoclonal antibody was developed. With sera from patients with different forms of the disease (n = 35), the overall sensitivity of the test was found to be 71.4%, while the specificity was found to be 98% with normal human sera from areas of endemicity (n = 44) and 85.4% with sera from patients with other chronic fungal or bacterial infections (n = 48). This novel, highly specific ELISA provides a significant addition to the existing diagnostic tests for the detection of histoplasmosis.

Histoplasmosis. Experience during outbreaks in Indianapolis and review of the literature

Histoplasmosis remains a common infection in endemic regions of North America and Latin America, causing a broad spectrum of clinical findings. Experience during recurrent outbreaks in Indianapolis has shown the importance of immunosuppressive conditions including the acquired immunodeficiency syndrome (AIDS) as a risk factor for disseminated disease and expanded our knowledge of the common clinical manifestations. Pericarditis, rheumatologic manifestations, esophageal compression, and sarcoidlike manifestations were found to be relatively common findings in histoplasmosis. These studies have established the useful role of serologic testing and have led to the discovery of antigen testing for diagnosis of histoplasmosis. This experience also has offered the opportunity to examine the outcome of treatment in persons with AIDS, contributing to studies that have found itraconazole to be an excellent alternative to amphotericin B in persons with mild or moderately severe infection.

Case report and review of disseminated histoplasmosis in South-East Asia: clinical and epidemiological implications

The South-East Asian region is not known to be a major endemic area for histoplasmosis. We have recently diagnosed several cases of disseminated histoplasmosis in patients from this region. We report on a well documented indigenous case of disseminated histoplasmosis in a 62-year-old poultry farmer and review the literature for other reported cases of clinical histoplasmosis in the South-East Asian region. Sporadic cases of indigenous chronic pulmonary and non-meningeal disseminated histoplasmosis in immunocompetent hosts have been reported as well as examples of disseminated histoplasmosis in immunocompromised hosts. These reports suggest that histoplasmosis is endemic to certain areas in South-East Asia and that there may be a large number of undiagnosed and subclinical cases. The recent advances in diagnostic tests for histoplasmosis are also reviewed with reference to the experience of using these tests in the reported case.

Aberrant Histoplasma capsulatum. Confirmation of identity by a chemiluminescence-labeled DNA probe

A cottony, light tan, filamentous fungus with pear-shaped microconidia and lacking tuberculated macroconidia was isolated from a bronchial lavage specimen. Subculture on several media at 37 degrees C failed to convert the fungus to a yeast form after several weeks; attempts at in vivo conversion in mice were also unsuccessful. Sera obtained several months apart showed M bands with Histoplasma capsulatum (HC) antigen by immunodiffusion and an increase in complement fixation titers with mycelial and yeast phase antigens of HC. Parallel identity was obtained on two occasions with exoantigen culture confirmation reagents for HC from Immuno-Mycologics as well as one of identity with Nolan reagents. Extracts from four Chrysosporium spp. strains had no identity reactions with HC with either kit. The fungus was identified as HC by the Accuprobe Histoplasma chemiluminescence-labeled DNA probe directed at ribosomal RNA, whereas all four Chrysosporium spp. isolates tested negative. DNA probes are a fast and accurate method to confirm the identity of aberrant fungal isolates.

Histoplasma capsulatum infection associated with continuous ambulatory peritoneal dialysis

Fungal infection has become increasingly more important in patients undergoing continuous ambulatory peritoneal dialysis. We report here a case of Histoplasma capsulatum infection in such a Hong Kong Chinese patient who presented with fever and peritonitis. Histoplasma capsulatum was isolated from the dialysis fluid and histoplasma antibody was detected in the serum. The patient responded to the combined treatment of fluconazole, 5-flurocytosine and amphotericin B. This is the first reported case of histoplasmosis in Hong Kong.

Correlation of Histoplasma capsulatum polysaccharide antigen with the severity of infection in murine histoplasmosis

We sought to determine if Histoplasma capsulatum polysaccharide antigen (HPA) levels correlate with the extent of infection in murine of histoplasmosis. Separate groups of mice were inoculated intratracheally with varying numbers of H. capsulatum yeast cells. After 1 week, HPA levels and fungal burden (quantitative culture of lung and spleen and histopathologic stain of lung) were determined in lung and spleen, and HPA levels in serum. HPA levels, cultures and histopathological stain results of lung and spleen tissue showed a direct correlation with increasing inoculum size. HPA levels in serum also correlated with the size of inoculum. H. capsulatum antigen in lung correlated with silver stain scores of lung tissue, (R = 0.948, P less than 0.001) and with quantitative culture scores of lung, (R = 0.929, P less than 0.001). HPA levels in spleen tissue also correlated with spleen culture scores, (R = 0.724, P less than 0.001). These results indicate that determination of HPA level in serum and tissue may be a useful test in evaluating the severity of diseases as well as efficacy of antifungal therapy in histoplasmosis.

Evaluation of lipoarabinomannan for the serological diagnosis of tuberculosis

The availability of highly purified lipoarabinomannan from Mycobacterium tuberculosis in its native acylated, highly antigenic state allowed its application to the serodiagnosis of tuberculosis in patients from the Republic of Mexico. Antilipoarabinomannan immunoglobulin G antibodies in sera from 66 patients with pulmonary, miliary, and pleural tuberculosis and tuberculosis lymphadenities were measured by using the enzyme-linked immunosorbent assay against sera from a control population of healthy individuals, people with histoplasmosis, and people with lung diseases not caused by mycobacteria. The results pointed to an unexpectedly high degree of specificity of 91% and a sensitivity of 72%, comparable to figures from previous studies with other purified antigens; most of the false-positive results were for patients with histoplasmosis. Thus, lipoarabinomannan of M. tuberculosis is a potentially useful antigen for the serodiagnosis of tuberculosis.

Preparation of monoclonal antibodies that differentiate between Histoplasma capsulatum variant capsulatum and H. capsulatum variant duboisii

The immunosuppressive drug cyclophosphamide was used to facilitate the production of monoclonal antibodies (Mabs) which differentiated between the yeast phase of the two variants of the dimorphic fungus Histoplasma capsulatum by both enzyme-linked immunosorbent assay and Western blot. Two Mabs are described, identifying epitopes on a 70-75 kDa molecule, which are specific to H. capsulatum var. capsulatum and which do not identify epitopes of H. capsulatum var. duboisii. These Mabs have potential use in the epidemiology and serodiagnosis of histoplasmosis in areas where both classical and African forms of the disease occur.

Evaluation of an ELISA for the detection of anti-Histoplasma ribosomal and antihistoplasmin antibodies in histoplasmosis

We have developed an indirect sandwich enzyme-lined immunosorbent assay (ELISA) for the detection of antibodies to Histoplasma ribosomes and histoplasmin; we used this test for demonstration of these antibodies in sera from proven cases of histoplasmosis and other infections. Serum dilutions from five negative controls used in each experiment were normalized against 50 normal sera, and a factor of the mean absorbance was used to establish a positive reaction. Antiribosomal antibodies were detected in 97% of the known histoplasmosis patients with ELISA titers ranging from 1:100 to over 1:12,800. In contrast, antibodies to histoplasmin were detected in only 75% of these sera; titers ranged from 1:100 to 1:12,800. Cross-reactions with sera from other fungal infections (blastomycosis, coccidioidomycosis, paracoccidioidomycosis, cryptococcosis, candidiasis, and aspergillosis) were seen in 46% of the cases with ribosomes and 37% with histoplasmin. Fifty percent of the sera from tuberculosis patients gave positive reactions with ribosomes and 29% with histoplasmin. These results warrant further studies on the significance of antibodies to ribosomes and histoplasmin in immunity to histoplasmosis.

Evaluation of an enzyme-linked immunosorbent assay that uses ferrous metal beads for determination of antihistoplasmal immunoglobulins G and M

A rapid enzyme-linked immunosorbent assay (ELISA) for the detection of human class-specific antibodies to Histoplasma capsulatum (histoplasmal immunoglobulin M [HIgM] and histoplasmal IgG [HIgG]) was developed by using antigen adsorbed onto polycarbonate-coated ferrous beads. In the ELISA method all the reagents used were commercially available. In 135 specimens from patients with confirmed histoplasmosis, sensitivities were 76% for complement fixation (CF), 53% for immunodiffusion (ID), and 64% for the ELISA for HIgM and HIgG combined. The ELISA detected histoplasmal antibody in 36% of the specimens with negative antibody titers by CF and 46% of the specimens with negative antibody titers by ID. The ELISA detected histoplasmal antibody in 27% of specimens that were negative by both CF and ID. When limited to specimens collected within 4 months of the onset of histoplasmosis symptoms, sensitivities were 82% for CF, 63% for ID, and 86% for ELISA for HIgG and HIgM combined. Within this group, ELISA detected histoplasmal antibody in 90% of the specimens that were negative by CF, 76% that were negative by ID, and 100% that were negative by both CF and ID. The specificity of the ELISA could not be fully addressed since sera from patients with other fungal infections were not available.

Diagnosis and management of histoplasmosis

Histoplasmosis occurs throughout the world but is more common within the endemic areas of North America, particularly in fertile river valleys. Disease manifestations range from asymptomatic infection in the normal host with low-inoculum exposure to rapidly fatal, disseminated infection in the severely immunocompromised host, emphasizing the importance of cellular immunity in defense against Histoplasma capsulatum. Diagnosis depends on a high index of suspicion, knowledge of the clinical and epidemiologic features of the infection, and a thorough understanding of the uses and limitations of fungal cultural and serological laboratory procedures. Recently, a method has been developed for rapid diagnosis based on detection of a polysaccharide antigen in body fluids of patients with histoplasmosis. Amphotericin B remains the preferred treatment for more severe forms of histoplasmosis, particularly in the immunocompromised host, but oral treatment with ketoconazole or newer imidozoles appears to be effective in less severe infections in non-immunocompromised individuals.

Serological techniques for diagnosis of fungal infection

This review summarizes recent developments in the serodiagnosis of candidiasis, aspergillosis, cryptococcosis, histoplasmosis, blastomycosis, coccidioidomycosis, mucormycosis and sporotrichosis. A number of studies have substantiated the presence of circulating antigens in invasive candidiasis, invasive aspergillosis, disseminated histoplasmosis and coccidioidomycosis, and immunoassays for antigen detection provide moderate sensitivity but high specificity for disease. Improved detection may result mainly from repeated serum or concentrated urine samplings rather than from the development of more sensitive immunoassays. Immunoblot analysis of the serological response is a useful tool for the identification of immunogenic fungal components that elicit a specific antibody response in invasive disease. This method, and others, have been successfully applied to the study of the immune response to several fungi, including Candida, Aspergillus and Rhizopus.

Production and characterization of murine monoclonal antibodies to Histoplasma capsulatum yeast cell antigens

Four monoclonal antibodies (MAbs) were produced by immunizing mice with a disrupted yeast cell homogenate of Histoplasma capsulatum. MAbs 1 and 2 reacted only with the yeast cell antigens of H. capsulatum and Blastomyces dermatitidis, whereas MAbs 3 and 4 showed broader cross-reactivity. MAb 3 cross-reacted with B. dermatitidis, Paracoccidioides brasiliensis, Sporothrix schenckii, and Candida albicans, and MAb 4 cross-reacted with B. dermatitidis, C. albicans, Coccidioides immitis, Aspergillus fumigatus, and Mycobacterium tuberculosis. All four MAbs exhibited unique specificity when reacted with three different strains of H. capsulatum (G217B, A811, and P-IN). MAb 1 belonged to the IgG2b subclass, MAb 3 belonged to the IgG1 subclass, and MAbs 2 and 4 belonged to the IgG3 subclass. MAbs 1, 2, and 3 formed bands in the Western immunoblot assay; the two dominant distinct bands had apparent molecular masses of 72 and 62 kilodaltons.

Predictive value of serologic tests in the diagnosis and follow-up of patients with paracoccidioidomycosis

A serologic study was undertaken in a group of 43 patients with active paracoccidioidomycosis who were treated in the same form (ketoconazole), for identical periods of time (6 months), and folio wed-up for various periods posttherapy. The tests employed were agar gel immunodiffusion (AGID) and complement fixation (FC). Also studied were 50 sera from patients with proven histoplasmosis and pulmonary aspergilloma, 30 patients with culturaly proven tuberculosis as well as 92 specimens from healthy individuals, residents in the endemic area for paracoccidioidomycosis. A single lot of yeast filtrate antigen was used throughout the study. The value of each test was measured according to GALEN and GAMBINO6. Both tests were highly sensitive, 89 and 93% respectively. Regarding their specificity, the AGID was totally specific while the CF exhibited 96.6% and 97% specificity in front of tuberculosis patients and healthy individuals respectively and 82% in comparison with patients with other mycoses. The concept of predictive value, that is, the certainty one has in accepting a positive test as diagnostic of paracoccidioidomycosis, favored the AGID procedure (100%) over the CF test. The latter could sort out with 93% certainty a patient with paracoccidioidomycosis among a group of healthy individuals and with 97.5% in the case of TB patients; when the group in question was composed by individuals with other deep mycoses, such certainty was lower (81%). The above results indicate that both the AGID and the CF tests furnish results of high confidence; one should not relay, however, in the CF alone as a means to establish the specific diagnosis of paracoccidioidomycosis.

Development of a comparative dot ELISA for the detection of antibodies in blastomycosis

We present a preliminary study utilizing an enzyme immunoassay for the detection of antibodies in blastomycosis using nitrocellulose membrane as the solid support. The comparative dot enzyme-linked immunosorbent assay (CDE) utilizing Blastomyces dermatitidis, Histoplasma capsulatum, and Coccidioides immitis antigens allows rapid screening of specimens and determination of a serum profile with respect to anti-Blastomyces antibodies. Sensitivity (76% or greater) and specificity (approximately 12% crossreactivity) determinations indicated that this visual assay may be an alternative antibody detection method for blastomycosis or other systemic fungal diseases.