Histoplasmosis: A systematic review to inform the World Health Organization of a fungal priority pathogens list.

Histoplasmosis, a significant mycosis primarily prevalent in Africa, North and South America, with emerging reports globally, poses notable health challenges, particularly in immunocompromised individuals such as people living with HIV/AIDS and organ transplant recipients. This systematic review, aimed at informing the World Health Organization's Fungal Priority Pathogens List, critically examines literature from 2011 to 2021 using PubMed and Web of Science, focusing on the incidence, mortality, morbidity, antifungal resistance, preventability, and distribution of Histoplasma. We also found a high prevalence (22%-44%) in people living with HIV, with mortality rates ranging from 21% to 53%. Despite limited data, the prevalence of histoplasmosis seems stable, with lower estimates in Europe. Complications such as central nervous system disease, pulmonary issues, and lymphoedema due to granuloma or sclerosis are noted, though their burden remains uncertain. Antifungal susceptibility varies, particularly against fluconazole (MIC: ≥32 mg/l) and caspofungin (MICs: 4-32 mg/l), while resistance to amphotericin B (MIC: 0.125-0.16 mg/l), itraconazole (MICs: 0.004-0.125 mg/l), and voriconazole (MICs: 0.004-0.125 mg/l) remains low. This review identifies critical knowledge gaps, underlining the need for robust, globally representative surveillance systems to better understand and combat this fungal threat.

Histoplasmosis in domestic cats: new minimally invasive diagnostic techniques.

OBJECTIVES: The aim of the present study was to evaluate minimally invasive diagnostic techniques, such as the semi-quantitative indirect IgG antibody enzyme immunoassay (EIA) using blood serum and the urinary lateral flow assay (LFA), for the detection of Histoplasma capsulatum in cats with histoplasmosis. METHODS: Eight client-owned domestic cats diagnosed with histoplasmosis were selected based on cytological, histopathological, mycological, molecular or antigenic techniques. The blood serum of these animals was tested in a semi-quantitative indirect IgG antibody EIA for the detection of H capsulatum. Urine samples were tested for H capsulatum antigen using LFA. RESULTS: Five cats were seropositive on IgG EIA (5/8, with diagnostic sensitivity equal to 62.5%; 95% confidence interval [CI] 24.5-91.5) and five cats were positive on H capsulatum antigen LFA (5/7, with diagnostic sensitivity equal to 71.4%; 95% CI 29.0-96.3). The combined diagnostic sensitivity when interpreted in parallel was 87.5% (7/8, 95% CI 47.3-99.7). The specificity for the anti-Histoplasma IgG EIA was 100% (95% CI 71.5-100) and for the H capsulatum antigen LFA it was also 100% (95% CI 71.5-100). CONCLUSIONS AND RELEVANCE: The semi-quantitative indirect IgG antibody EIA for the detection of H capsulatum in blood serum and the urinary LFA for the detection of the same agent emerge as new minimally invasive diagnostic techniques that can assist in the approach to disseminated and pulmonary feline histoplasmosis, especially when both techniques are considered together.

Rare Case of Disseminated Histoplasmosis Mitral Valve Endocarditis in Florida.

BACKGROUND Histoplasma capsulatum is prevalent in the mid-eastern United States and is an environmental fungus that causes human infection by the inhalation of its spores. It is commonly associated with areas containing large amounts of bird excrement and can survive for years in the soil. Only 1% of infected individuals develop disseminated histoplasmosis or Histoplasma endocarditis. CASE REPORT A 61-year-old man with atrial fibrillation had 8 months of fatigue, low-grade fevers, night sweats, and unexplained weight loss presented to the Emergency Department. He worked and lived in Central Florida and although he raised cattle, he denied exposure to birds or bats with regularity. A transesophageal echocardiogram confirmed a sessile echo density on the atrial surface of the mitral valve. His microbial Karius cell-free DNA test from his blood sample was positive for Histoplasma capsulatum, and he was immediately given intravenous liposomal amphotericin for 2 weeks. A tissue valve was used to successfully replace his mitral valve along with a coronary artery bypass and a maze procedure for his persistent atrial fibrillation and atrial flutter. The diagnosis of mitral valve endocarditis from disseminated histoplasmosis was confirmed by pathological analysis, and he was sent home on long-term itraconazole maintenance treatment. CONCLUSIONS Surgical intervention in combination with anti-fungal medication can be a lifesaving intervention for disseminated histoplasmosis. A thorough history is particularly important when evaluating a patient with an unknown infectious source, especially assessing for risk factors, including exposure to environmental factors, workplace, and animals.

Genotypic diversity, virulence, and molecular genetic tools in Histoplasma.

SUMMARYHistoplasmosis is arguably the most common fungal respiratory infection worldwide, with hundreds of thousands of new infections occurring annually in the United States alone. The infection can progress in the lung or disseminate to visceral organs and can be difficult to treat with antifungal drugs. Histoplasma, the causative agent of the disease, is a pathogenic fungus that causes life-threatening lung infections and is globally distributed. The fungus has the ability to germinate from conidia into either hyphal (mold) or yeast form, depending on the environmental temperature. This transition also regulates virulence. Histoplasma and histoplasmosis have been classified as being of emergent importance, and in 2022, the World Health Organization included Histoplasma as 1 of the 19 most concerning human fungal pathogens. In this review, we synthesize the current understanding of the ecological niche, evolutionary history, and virulence strategies of Histoplasma. We also describe general patterns of the symptomatology and epidemiology of histoplasmosis. We underscore areas where research is sorely needed and highlight research avenues that have been productive.

Phenotypic characterization of cryptic species in the fungal pathogen Histoplasma.

Histoplasmosis is an endemic mycosis that often presents as a respiratory infection in immunocompromised patients. Hundreds of thousands of new infections are reported annually around the world. The etiological agent of the disease, Histoplasma, is a dimorphic fungus commonly found in the soil where it grows as mycelia. Humans can become infected by Histoplasma through inhalation of its spores (conidia) or mycelial particles. The fungi transition into the yeast phase in the lungs at 37°C. Once in the lungs, yeast cells reside and proliferate inside alveolar macrophages. Genomic work has revealed that Histoplasma is composed of at least five cryptic phylogenetic species that differ genetically. Three of those lineages have received new names. Here, we evaluated multiple phenotypic characteristics (colony morphology, secreted proteolytic activity, yeast size, and growth rate) of strains from five of the phylogenetic species of Histoplasma to identify phenotypic traits that differentiate between these species: Histoplasma capsulatum sensu stricto, Histoplasma ohiense, Histoplasma mississippiense, Histoplasma suramericanum, and an African lineage. We report diagnostic traits for three species. The other two species can be identified by a combination of traits. Our results suggest that (i) there are significant phenotypic differences among the cryptic species of Histoplasma and (ii) those differences can be used to positively distinguish those species in a clinical setting and for further study of the evolution of this fungal pathogen.IMPORTANCEIdentifying species boundaries is a critical component of evolutionary biology. Genome sequencing and the use of molecular markers have advanced our understanding of the evolutionary history of fungal pathogens, including Histoplasma, and have allowed for the identification of new species. This is especially important in organisms where morphological characteristics have not been detected. In this study, we revised the taxonomic status of the four named species of the genus Histoplasma, H. capsulatum sensu stricto (ss), H. ohiense, H. mississippiense, and H. suramericanum, and propose the use of species-specific phenotypic traits to aid their identification when genome sequencing is not available. These results have implications not only for evolutionary study of Histoplasma but also for clinicians, as the Histoplasma species could determine the outcome of disease and treatment needed.

Molecular detection of Histoplasma capsulatum in organ samples from bats randomly captured in urban areas of Araraquara, São Paulo state, Brazil.

The mycosis histoplasmosis is also considered a zoonosis that affects humans and other mammalian species worldwide. Among the wild mammals predisposed to be infected with the etiologic agent of histoplasmosis, bats are relevant because they are reservoir of Histoplasma species, and they play a fundamental role in maintaining and spreading fungal propagules in the environments since the infective mycelial phase of Histoplasma grows in their accumulated guano. In this study, we detected the fungal presence in organ samples of bats randomly captured in urban areas of Araraquara City, São Paulo, Brazil. Fungal detection was performed using a nested polymerase chain reaction to amplify a molecular marker (Hcp100) unique to H. capsulatum, which revealed the pathogen presence in organ samples from 15 out of 37 captured bats, indicating 40.5% of infection. Out of 22 Hcp100-amplicons generated, 41% corresponded to lung and trachea samples and 59% to spleen, liver, and kidney samples. Data from these last three organs suggest that bats develop disseminated infections. Considering that infected bats create environments with a high risk of infection, it is important to register the percentage of infected bats living in urban areas to avoid risks of infection to humans, domestic animals, and wildlife.

Survival Against the Odds-Hemophagocytic Lymphohistiocytosis Amidst the Shadows of Disseminated Histoplasmosis: A Case Report and Literature Review.

Hemophagocytic lymphohistiocytosis (HLH) secondary to Histoplasma capsulatum is rare, impacting <1% globally, with a mortality rate of up to 31%. Herein, we present a rare case of HLH secondary to H capsulatum, affecting a 57-year-old female with rheumatoid arthritis. Extensive investigations were unrevealing and despite broad-spectrum antibiotics, her condition worsened, leading to respiratory failure requiring extracorporeal membrane oxygenation (ECMO) support, shock requiring multiple vasopressors, and acute kidney injury (AKI) requiring hemodialysis. Diagnosis confirmed disseminated histoplasmosis (DHP), prompting Amphotericin B and methylprednisolone treatment, resulting in significant improvement and discharge with posaconazole therapy. Secondary HLH, primarily arising from severe infections like DHP, is discussed. Limited research exists on this condition in human immunodeficiency virus (HIV)-seronegative individuals. Diagnosis involves HLH-2004 and HScore criteria. Managing histoplasmosis-associated HLH remains challenging due to multiorgan failure risks and treatment complexities and needs further research.

Hepatic insufficiency in two juvenile dogs with histoplasmosis.

A 9-month-old female intact toy poodle and a 1-year-old female intact Labrador retriever mix presented to separate teaching hospitals for chronic histories of malaise and clinicopathologic evidence of hepatic dysfunction. The signalment and clinical histories of these dogs prompted consideration of a congenital portosystemic shunt as a primary differential. However, microscopic evaluation of peritoneal effusion, pleural effusion, and peripheral blood samples from the dogs revealed round to ovoid yeast organisms morphologically most compatible with Histoplasma capsulatum. Additional testing confirmed histoplasmosis in each case. The poodle underwent a computed tomography (CT) study, which showed hepatomegaly with a spleno-gonadal shunt, pancreatic and gastric wall edema, and marked peritoneal effusion, findings compatible with portal hypertension and secondary acquired shunt formation. The dog was later humanely euthanized due to clinical deterioration, and on necropsy hepatic histoplasmosis was verified, with additional affected tissues comprising lungs and spleen. The Labrador Retriever mix responded clinically and clinicopathologically to antifungal therapy, though no abdominal imaging was performed to definitively exclude the possibility of a congenital portosystemic shunt. In retrospect, several features were more compatible with histoplasmosis than portosystemic shunt in these cases, including hyperbilirubinemia, effusion, and hepatomegaly. These findings serve as a reminder of the need to interpret serum biochemical findings in the context of the totality of the clinicopathologic data and imaging findings, as well as the diagnostic value of microscopy in the evaluation of hematologic and body cavity fluid samples.

Tracing histoplasmosis genomic epidemiology and species occurrence across the USA.

ABSTRACTHistoplasmosis is an endemic mycosis in North America frequently reported along the Ohio and Mississippi River Valleys, although autochthonous cases occur in non-endemic areas. In the United States, the disease is provoked by two genetically distinct clades of Histoplasma capsulatum sensu lato, Histoplasma mississippiense (Nam1) and H. ohiense (Nam2). To bridge the molecular epidemiological gap, we genotyped 93 Histoplasma isolates (62 novel genomes) including clinical, environmental, and veterinarian samples from a broader geographical range by whole-genome sequencing, followed by evolutionary and species niche modelling analyses. We show that histoplasmosis is caused by two major lineages, H. ohiense and H. mississippiense; with sporadic cases caused by H. suramericanum in California and Texas. While H. ohiense is prevalent in eastern states, H. mississipiense was found to be prevalent in the central and western portions of the United States, but also geographically overlapping in some areas suggesting that these species might co-occur. Species Niche Modelling revealed that H. ohiense thrives in places with warmer and drier conditions, while H. mississippiense is endemic to areas with cooler temperatures and more precipitation. In addition, we predicted multiple areas of secondary contact zones where the two species co-occur, potentially facilitating gene exchange and hybridization. This study provides the most comprehensive understanding of the genomic epidemiology of histoplasmosis in the USA and lays a blueprint for the study of invasive fungal diseases.

Histoplasma capsulatum tenosynovitis: An unusual presentation in a kidney transplant recipient.

Histoplasmosis is an expected endemic mycosis in solid organ transplant recipients and occurs as a primary infection, reactivation, or, rarely, acquired from an infected allograft. Reactivation is favored by maintenance immunosuppression or anti-rejection therapy, which facilitates the appearance of disseminated forms as well as unusual presentations. We present the case of a 66-year-old woman with isolated tenosynovitis due to Histoplasma capsulatum 25 years after a kidney transplant.

Epidemiological, clinical, diagnostic, and therapeutic features of histoplasmosis: A systematic review.

Histoplasmosis is a mycosis due to a dimorphic fungus Histoplasma capsulatum. This study aimed at providing an overview of histoplasmosis epidemiological, clinical, diagnostic, and therapeutic aspects from the last 30 years. This review was carried out using a systematic literature search on histoplasmosis from 1992 to 2021. We describe the clinical features, diagnostic methods and treatment. Empirical searches were conducted via the databases PubMed, Google Scholar and Science Direct. Between 1992 and 2021, 190 manuscripts were published and reported 212 cases of histoplasmosis. These publications included 115 and 97 cases of American and African histoplasmosis respectively. The number of publications increased over the last ten years with a maximum in 2020 (12.34 % of the cases reported). The disseminated forms of histoplasmosis were the most frequently reported cases as compared to the localized forms. This was the case with the American histoplasmosis (75.65 %) as well as with the African histoplasmosis (55.67 %). Itraconazole (31.17 %) and Amphotericin B (26.62 %) were the most used drugs in the management of these cases. American histoplasmosis is distributed worldwide whereas African histoplasmosis is mainly present in intertropical Africa. There is a critical need for setting up a global surveillance system, towards a better understanding of the disease.

Histoplasma antigens as novel players for the development of new enzyme immunoassays for the serodiagnosis of histoplasmosis: A comparative study of their analytical performance.

Definitive diagnosis of histoplasmosis relies on culture and/or cytology/histopathology; however, these procedures have limited sensitivity and cultures are time-consuming. Antibodies detection by immunodiffusion has low sensitivity in immunocompromised individuals and uses histoplasmin (HMN), a crude antigenic extract, as reagent. Novel protein antigen candidates have been recently identified and produced by DNA-recombinant techniques to obtain standardized and specific reagents for diagnosing histoplasmosis. To compare the analytical performance of novel enzyme-linked immunosorbent assays (ELISAs) for antibodies testing for diagnosing histoplasmosis using different Histoplasma capsulatum antigens as reagents. The H. capsulatum 100 kDa protein (Hcp100), the M antigen and its immunoreactive fragment F1 were produced by DNA-recombinant techniques. Galactomannan was purified from both the yeast and mycelial cell walls (yGM and mGM, respectively). The analytical performance of the ELISA tests for the serological detection of antibodies against these antigens was evaluated and compared with those obtained using HMN as reagent. Antibodies detection by the Hcp100 ELISA demonstrated 90.0% sensitivity and 92.0% specificity, versus 43.3% sensitivity and 95.0% specificity of the M ELISA, 33.3% sensitivity and 84.0% specificity of the F1 ELISA, 96.7% sensitivity and 94.0% specificity of the yGM ELISA, 83.3% sensitivity and 88.0% specificity of the mGM ELISA, and 70.0% sensitivity and 86.0% specificity for the HMN ELISA. In summary, Hcp100 is proposed as the most promising candidate for the serodiagnosis of histoplasmosis. The primary immunoreactive element in HMN proved to be GM rather than the M antigen. Nevertheless, a higher incidence of cross-reactions was noted with GM compared to M.

Hcp100 is a promising serodiagnostic candidate for histoplasmosis, boasting high sensitivity and specificity. Notably, GM, rather than M antigen, emerged as the primary immunoreactive element in HMN, despite a higher incidence of cross-reactions with GM compared to M.

Pulmonary histoplasmosis on the Chinese mainland: two case reports and literature review.

INTRODUCTION: Pulmonary histoplasmosis is a fungal disease that is endemic in North and Central America. It is relatively rare in China and commonly misdiagnosed as tuberculosis or cancer due to nonspecific clinical and radiographic manifestations. Rapid and accurate pathogen tests are critical for the diagnosis of pulmonary histoplasmosis. METHODOLOGY: We report two cases of pulmonary histoplasmosis. We collected all the relevant case reports on the Chinese mainland (from 1990 to 2022) to analyze features of this disease among Chinese patients. RESULTS: A total of 42 articles reporting 101 cases were identified, and the two cases reported in this article were also included for analysis. Sixty-three (61.2%) patients had respiratory symptoms and 35 (34.0%) patients were asymptomatic. The most common radiographic findings were pulmonary nodules or masses (81.6%). Twenty-two (21.4%) patients were misdiagnosed as tuberculosis, and 37 (35.9%) were misdiagnosed as lung tumors before pathological findings. Metagenomic next­generation sequencing (mNGS) testing provided a rapid diagnostic and therapeutic basis for three patients. CONCLUSIONS: Clinical features and imaging findings of pulmonary histoplasmosis are not specific. Relevant epidemiological history and timely pathogen detection are important for diagnosis. mNGS can shorten the time required for diagnosis and allow earlier initiation of targeted antibiotic therapy.

Histoplasmosis in HIV/AIDS patients in Amazonas, Northern Brazil.

Histoplasmosis is commonly observed in AIDS patients as a neglected opportunistic disease that has an important relationship with environmental factors. The present study described the clinical characteristics of HIV/AIDS patients diagnosed with disseminated histoplasmosis in a tertiary healthcare facility in Manaus, Amazonas, Brazil, and evaluated the patients' homes and urban environmental samples as a source of exposure to Histoplasma capsulatum. A review of medical records from 2017 to 2019 of patients with HIV/AIDS associated with histoplasmosis was carried out, as well as the collection of environmental samples in the homes of these patients. These samples were subjected to DNA extraction and then subjected to qPCR. A total of 62 patients diagnosed with HIV/AIDS and histoplasmosis were identified, which corresponds to 4.5% (n = 62/1372) of the HIV/AIDS cases detected in the period. Of these, 68% (n = 42/62) were male, with a mean age of 36 years and low education. In 47% (n = 29/62) of the cases, the diagnosis of HIV/AIDS and histoplasmosis occurred simultaneously. Mortality was 45% (n = 28/62), and 68% (n = 42/62) of these patients did not regularly use highly active antiretroviral therapy. The main symptoms found were respiratory, gastrointestinal, and weight loss, and in 81% (n = 50/62), the place of residence was in an urban area. A total of 57 environmental samples were analyzed, and the presence of Histoplasma capsulatum was not detected in any of the analyzed samples. There was a high mortality rate in the studied group of patients with AIDS and histoplasmosis. Most patients reported residing in urban areas of Manaus, with no history of travel to other areas previously known as being high risk for histoplasmosis.

Validation of a real-time polymerase chain reaction for the detection and quantification of the nucleic acid of Histoplasma from equine clinical samples.

Histoplasma capsulatum var. farciminosum (HCF) is a dimorphic fungus that causes epizootic lymphangitis in equids. Current diagnostic approaches, including culture, microscopy, and clinical presentation, lack speed, sensitivity, and specificity when diagnosing clinical cases. In this study, equine blood and pus samples on Whatman FTA cards from Senegal (n = 3), The Gambia (n = 19), Ethiopia (n = 16), and Mali (n = 13) were tested using a real-time PCR (qPCR) protocol. The assay was optimized and tested for its suitability to detect and quantify HCF in blood and pus loaded onto Whatman FTA cards at sampling. Whatman FTA cards were tested for their suitability for use with qPCR and were found to recover DNA more efficiently than from direct extraction. Using TaqMan fluorescent probes and specific primers, the assay demonstrated 100% analytical specificity when detecting multiple strains of Histoplasma and no false positives with off-target organisms. The assay's diagnostic performance was measured against an existing nested internal transcribed spacer PCR protocol using a receiver operating characteristic curve. The test was found to have a diagnostic specificity and sensitivity of 100% and 71.4%, respectively, when analyzing pus samples using a cycle threshold (Ct) cutoff determined by Youden's index (27.75). Blood sample cutoff Ct value was proposed at 34.55. Further optimization is required to improve the performance of the protocol when applied to blood samples. This study has, for the first time, demonstrated the ability to detect and quantify the DNA of Histoplasma spp. in equine blood and pus samples with a high degree of accuracy, providing a platform to further investigate the pathogenesis and epidemiology of this disease. IMPORTANCE: Histoplasmosis is a neglected yet major cause of morbidity and mortality in both equids and people in resource-scarce settings. One of the major hindrances to the control of histoplasmosis is a lack of readily available diagnostic tests. Tests are needed to support clinical decision-making and to be applied in population-based research to further understand this disease in situ. This paper reports, for the first time, the validation and application of a qPCR to detect Histoplasma directly from equine clinical samples, bypassing the need to culture this notoriously difficult organism. We report and comment on the performance of the qPCR in comparison with our previously developed nested PCR.

ß-1,3-Glucan recognition by Acanthamoeba castellanii as a putative mechanism of amoeba-fungal interactions.

In this study, we conducted an in-depth analysis to characterize potential Acanthamoeba castellanii (Ac) proteins capable of recognizing fungal ß-1,3-glucans. Ac specifically anchors curdlan or laminarin, indicating the presence of surface ß-1,3-glucan-binding molecules. Using optical tweezers, strong adhesion of laminarin- or curdlan-coated beads to Ac was observed, highlighting their adhesive properties compared to controls (characteristic time τ of 46.9 and 43.9 s, respectively). Furthermore, Histoplasma capsulatum (Hc) G217B, possessing a ß-1,3-glucan outer layer, showed significant adhesion to Ac compared to a Hc G186 strain with an α-1,3-glucan outer layer (τ of 5.3 s vs τ 83.6 s). The addition of soluble ß-1,3-glucan substantially inhibited this adhesion, indicating the involvement of ß-1,3-glucan recognition. Biotinylated ß-1,3-glucan-binding proteins from Ac exhibited higher binding to Hc G217B, suggesting distinct recognition mechanisms for laminarin and curdlan, akin to macrophages. These observations hinted at the ß-1,3-glucan recognition pathway's role in fungal entrance and survival within phagocytes, supported by decreased fungal viability upon laminarin or curdlan addition in both phagocytes. Proteomic analysis identified several Ac proteins capable of binding ß-1,3-glucans, including those with lectin/glucanase superfamily domains, carbohydrate-binding domains, and glycosyl transferase and glycosyl hydrolase domains. Notably, some identified proteins were overexpressed upon curdlan/laminarin challenge and also demonstrated high affinity to ß-1,3-glucans. These findings underscore the complexity of binding via ß-1,3-glucan and suggest the existence of alternative fungal recognition pathways in Ac.IMPORTANCEAcanthamoeba castellanii (Ac) and macrophages both exhibit the remarkable ability to phagocytose various extracellular microorganisms in their respective environments. While substantial knowledge exists on this phenomenon for macrophages, the understanding of Ac's phagocytic mechanisms remains elusive. Recently, our group identified mannose-binding receptors on the surface of Ac that exhibit the capacity to bind/recognize fungi. However, the process was not entirely inhibited by soluble mannose, suggesting the possibility of other interactions. Herein, we describe the mechanism of ß-1,3-glucan binding by A. castellanii and its role in fungal phagocytosis and survival within trophozoites, also using macrophages as a model for comparison, as they possess a well-established mechanism involving the Dectin-1 receptor for ß-1,3-glucan recognition. These shed light on a potential parallel evolution of pathways involved in the recognition of fungal surface polysaccharides.