Disseminated histoplasmosis in immunologically suppressed patients. Occurrence in a nonendemic area

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.

Gastrointestinal histoplasmosis with small intestinal perforation: 20-year experience

Postmortem studies show gastrointestinal tract involvement in as many as 70% of patients affected by disseminated histoplasmosis. Although gastrointestinal involvement is common in disseminated disease, the presentation of small intestinal perforation is exceedingly rare with few reported cases in the literature. Herein we present our institutional case series. The aim of the study is to describe small intestinal perforation in gastrointestinal histoplasmosis with attention to management and outcomes. This is a retrospective single-institution review of patients ≥ 18 years of age treated for small intestinal perforation due to gastrointestinal histoplasmosis. A prospectively maintained institutional database was searched from 2002 to 2022. Data obtained included demographics, comorbidities, treatment course, and outcomes. Five patients with a mean age of 54 years (range 25-72) were identified. Pertinent underlying comorbid conditions included Crohn's disease, psoriatic arthritis, rheumatoid arthritis, and solid organ transplantation. All patients were on chronic immunosuppressive medication(s) with the most common being tumor necrosis factors alpha inhibitors and corticosteroids. Four had a clinical diagnosis of perforation based on physical examination and imaging. All patients underwent segmental resection(s) of the small intestine and received medical treatment with intravenous amphotericin B and eventual transition to an oral antifungal. No patients experienced complications related to surgery. The limitations of the study include nonrandomized retrospective review, single-institution experience, and small patient sample size. Although rare, histoplasmosis should be considered in the differential of patients on chronic immunosuppressive therapy who present with gastrointestinal symptoms concerning perforation, especially from endemic areas. Small intestinal perforation due to gastrointestinal histoplasmosis can be successfully treated with resection and antifungal therapy.

Disseminated Histoplasmosis Presenting as Acute Respiratory Distress Syndrome and Disseminated Intravascular Coagulation in an HIV Positive Immigrant from Central America

Histoplasmosis rarely causes significant illness in immunocompetent patients. In endemic areas such as the Midwestern United States and Central America, most people are infected, but are rarely symptomatic, with variable presentation. The illness is usually self-limited in immunocompetent individuals. However, in immunocompromised patients, Histoplasma capsulatum can disseminate to various organs and should be suspected especially in the endemic areas or if there is a significant travel history involving these areas. We present a case of a 65-year-old male originally from Central America with no known past medical history presenting with Acute Respiratory Distress Syndrome complicated by disseminated intravascular coagulation due to acute histoplasmosis and incidentally found to have HIV/AIDS.

Concomitant onset of systemic lupus erythematosus and disseminated histoplasmosis: a case-based review

INTRODUCTION

Concomitant infections during the debut or relapse of systemic lupus erythematosus are a common scenario, due to multiple mechanisms including the use of immunosuppressive drugs and autoimmunity per se. Invasive fungal infections are rare in systemic lupus erythematosus and are associated with profound immunosuppressed states. Disseminated histoplasmosis in patients with lupus has rarely been reported and the concomitant presentation of both entities is exceptional.

METHODS

We describe a case and performed a literature review in order to identify all case reports. A literature search was carried out using in PubMed/MEDLINE, EMBASE and Google Scholar (the first 200 relevant references) bibliographic databases. All available inclusion studies from January 1968 through July 2020. All data were tabulated, and outcomes were cumulatively analyzed.

RESULTS

Thirty-one additional cases were identified. Disseminated histoplasmosis was the most common clinical presentation and most cases have been reported in patients with a prior diagnosis of lupus in the setting of moderate to high steroid dose use, usually in combination with some other immunosuppressant. Description at systemic lupus disease onset was only reported in 3 cases with a high associated mortality. In our patient, severe disease activity, significant immunosuppression, malnutrition and multi-organ compromise conditioned the patient's fatal outcome.

CONCLUSION

Histoplasmosis can closely mimic activity of lupus. Thus, early clinical recognition is important since a delay in diagnosis and treatment can lead to fatal outcomes.

Immunotherapy against Systemic Fungal Infections Based on Monoclonal Antibodies

The increasing incidence in systemic fungal infections in humans has increased focus for the development of fungal vaccines and use of monoclonal antibodies. Invasive mycoses are generally difficult to treat, as most occur in vulnerable individuals, with compromised innate and adaptive immune responses. Mortality rates in the setting of our current antifungal drugs remain excessively high. Moreover, systemic mycoses require prolonged durations of antifungal treatment and side effects frequently occur, particularly drug-induced liver and/or kidney injury. The use of monoclonal antibodies with or without concomitant administration of antifungal drugs emerges as a potentially efficient treatment modality to improve outcomes and reduce chemotherapy toxicities. In this review, we focus on the use of monoclonal antibodies with experimental evidence on the reduction of fungal burden and prolongation of survival in in vivo disease models. Presently, there are no licensed monoclonal antibodies for use in the treatment of systemic mycoses, although the potential of such a vaccine is very high as indicated by the substantial promising results from several experimental models.

Histoplasma capsulatum Infection in an Allogeneic Hematopoietic Stem Cell Transplant Patient Receiving Voriconazole Prophylaxis

Histoplasma capsulatum infection is a rare complication in the allogeneic stem cell transplant patients. Minimal guidance exists on how to appropriately manage histoplasmosis in these patients. We report a patient who developed Histoplasma pneumonia while receiving voriconazole prophylaxis at a therapeutic trough level. The patient experienced significant clinical improvement after initiation of itraconazole pharmacotherapy. We recommend a lower threshold for evaluation for histoplasmosis in allogeneic hematopoietic stem cell transplant recipients who live in endemic regions, regardless of their antifungal prophylactic regimen.

Progressive disseminated histoplasmosis with concomitant disseminated nontuberculous mycobacterial infection in a patient with AIDS from a nonendemic region (California)

Background

Opportunistic infections, while well studied in the AIDS population, continue to have variable and surprising presentations. Here, we present a case of disseminated histoplasmosis with disseminated nontuberculous mycobacterial infection in a 50 year old man with long standing AIDS living in a non-endemic area.

Case presentation

Patient presented with a constellation of symptoms, and imaging of the chest showed a pulmonary mass with cavitation, multiple nodules, and ground glass opacities. Further investigations revealed granulomatous lung nodules and fungemia consistent with Histoplasma capsulatum, and coinfection with disseminated nontuberculous mycobateria in a nonendemic area.

Conclusions

Immunocompromised patients risk co-inhabitation by multiple infectious organisms. Some of these organisms may preside in the host for years prior to reactivation. Clinicians in non endemic areas should therefore be careful to not overlook specific organisms based on a lack of a recent travel history. Physicians in nonendemic areas should become more familiar with the clinical findings and diagnostic approach of infectious such as Histoplasmosis, to ensure earlier recognition and treatment in immunocompromised individuals.

Extrahepatic biliary obstruction: an unusual presentation of hepatic sarcoidosis

We report this case of a 63-year-old woman who presented with progressive illness characterized by abdominal pain, weight loss, anorexia, generalized weakness, and fatigue. The patient was found to have obstructive jaundice with multiple mass lesions in the liver, spleen, and kidney on computed tomography scan of abdomen. She developed cholangitis, necessitating an emergent endoscopic retrograde cholangiopancreatography with biliary stenting and decompression. Later, she was found to have hepatic sarcoidosis on wedge biopsy of the liver. Extrinsic compression of biliary tree from mass effect of sarcoid granulomas with superimposed biliary sepsis is rare.

Granulomatous liver disease

Hepatic granulomata are not infrequently encountered in liver biopsy and often are associated with systemic disease. The clinical presentation varies with the particular systemic process. From a biochemical standpoint, the most common abnormalities are elevated serum alkaline phosphatase and γ-glutamyltransferase. The observation of granulomata in a liver biopsy specimen warrants workup to identify a possible cause. Clues may be obtained in the medical history, on physical examination, or with specialized blood testing or radiologic studies. Treatment involves therapy of the underlying cause of the disease associated with the development of the granulomatous hepatitis.

Surface architecture of histoplasma capsulatum

The dimorphic fungal pathogen Histoplasma capsulatum is the most frequent cause of clinically significant fungal pneumonia in humans. H. capsulatum virulence is achieved, in part, through diverse and dynamic alterations to the fungal cell surface. Surface components associated with H. capsulatum pathogenicity include carbohydrates, lipids, proteins, and melanins. Here, we describe the various structures comprising the cell surface of H. capsulatum that have been associated with virulence and discuss their involvement in the pathobiology of disease.

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.

Blastomycosis in solid organ transplant recipients

BACKGROUND

Blastomyces dermatitidis, the etiologic agent of blastomycosis, causes severe disease and substantial mortality in those immunocompromised by acquired immunodeficiency syndrome or malignancy. In solid organ transplant recipients, the epidemiology, clinical features, and outcomes have not been fully described.

METHODS

We conducted a retrospective case-series at the University of Wisconsin Hospital and Clinics. Case patients were solid organ transplant recipients with blastomycosis.

RESULTS

From 1986 to 2004, we identified 11 cases of post-transplant blastomycosis with 64% occurring between 2000 and 2004. Onset of infection occurred a median of 26 months post transplantation with near equal distribution before and after the first year of transplantation. Rejection did not precede any case of post-transplant blastomycosis. Opportunistic co-infections were common, occurring in 36% of patients. Pneumonia was the most common clinical presentation and was frequently complicated by acute respiratory distress syndrome (ARDS). Extrapulmonary disease predominantly involved the skin and spared the central nervous system. The overall mortality rate was 36%; however, this increased to 67% in those with ARDS. None of the surviving patients relapsed or received routine secondary antifungal prophylaxis.

CONCLUSION

Blastomycosis is an uncommon infection following solid organ transplantation that is frequently complicated by ARDS, dissemination, and opportunistic co-infection. After cure, post-transplant blastomycosis may not require lifelong antifungal suppression.

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.

Fungal infections in solid organ transplantation

Fungal infections in solid organ transplant recipients continue to be a significant cause of morbidity and mortality. Candida spp. and Aspergillus spp. account for most invasive fungal infections. The incidence of fungal infection varies with type of solid organ transplant. Liver transplant recipients have highest reported incidence of candida infections while lung transplant recipients have highest rate of Aspergillus infections. Recent epidemiological studies suggest the emergence of resistant strains of candida as well as mycelial fungi other than Aspergillus in these patients. The current review incorporates the recent changes in the epidemiology of fungal infections in solid organ transplant recipients and highlights the newer data on the diagnosis, prophylaxis and treatment of fungal infections in these patients.

Chest Pain Resulting From Histoplasmosis Pericarditis

Histoplasmosis is an endemic disease in many regions of the United States. Physicians must be aware of the clinical syndromes and take advantage of epidemiologic clues when diagnosing histoplasmosis pericarditis. Clinicians must also be familiar with the uses and limitations of a battery of serologic and mycologic tests. Finally, further clinical trials are needed to study the role of antifungal therapy in the treatment of histoplasmosis pericarditis.

Histoplasmosis: a review for clinicians from non-endemic areas

Histoplasmosis is an important systemic mycosis in the Americas, Asia, and Africa. Increasingly cases are recognised in nonendemic areas. Proper management requires recognition of the clinical syndromes caused by Histoplasma capsulatum infection, familiarity with the uses and limitations of the diagnostic tests, an understanding of the indications for treatment and role of specific antifungal agents. This review will address these issues with the goal of providing physicians in non-endemic areas sufficient information to suspect, diagnose, and treat patients with histoplasmosis.

Unusual orofacial manifestations of histoplasmosis in renal transplanted patient

Histoplasmosis is a fungal infection caused by the Histoplasma capsulatum. Mucosal manifestations are uncommon, but, when present, they are usually associated with pulmonary or chronic disseminated infection. The course of the disease is often related to the host immune response. The purpose of this article is to describe the clinical and microscopic findings of unusual involvement of nasal cartilage and septal destruction, and oral lesions of histoplasmosis in an immunosuppressed patient who presented an unusual form of the disease.

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.

Oral histoplasmosis in an HIV-negative patient

Histoplasmosis is a deep mycosis caused by Histoplasma capsulatum, which has been found in soil with accumulated excreta of bats and birds. This disease has variable clinical findings with only pulmonary or systemic involvement. Upper aerodigestive lesions are found mainly associated with systemic disease, affecting particularly patients with immunosuppression conditions mainly caused by HIV. However, it is uncommon in immunocompetent patients. This report describes a case of oro-laryngeal-esophageal histoplasmosis in a HIV-seronegative patient without detectable systemic involvement.

Progressive Disseminated Histoplasmosis Presenting as Cellulitis in a Renal Transplant Recipient

With the advent of potent immunosuppressive therapies used in solid organ transplantation, patients are more susceptible to a variety of infectious organisms. Infections may result from atypical pathogens and present in an unusual manner. We describe a case of progressive disseminated histoplasmosis presenting as cellulitis in a renal transplant recipient and review this disease.

Endobronchial histoplasmosis: a masquerade of primary endobronchial neoplasia--a clinical study of four cases

BACKGROUND

Histoplasma capsulatum is a dimorphic fungus with both hyphal and microconidial elements and is endemic in certain areas of the central United States. Most clinically recognized syndromes are self-limited, presenting in more than 80% of cases as an influenza-like acute pulmonary illness. We encountered four patients with an endobronchial presentation of histoplasmosis masquerading as a bronchogenic malignancy.

METHODS

The patient files from one of the authors (PR) uncovered four patients diagnosed with, and treated for, endobronchial histoplasmosis; all cases were referred for a presumptive diagnosis of endobronchial neoplasia.

RESULTS

The case study group comprised three women, ages 52, 68, and 81 years, respectively, and one man age 29 years, all presenting with recurrent hemoptysis. An obstructing adherent lesion was apparent on bronchoscopy in three, involving the right upper lobe bronchus in two, and right mainstem bronchus in one. In one patient, blood was observed in the bronchus intermedius; there was no gross lesion. Recurrent hemoptysis necessitated a right upper sleeve lobectomy in one, a right upper lobe lobectomy and right lower wedge resection in one, a right middle lobectomy in one, and wedge resection of the right upper lobe in one.

CONCLUSIONS

Endobronchial histoplasmosis may mimic primary bronchogenic carcinoma, presenting as a fixed obstructing endobronchial lesion associated with hemoptysis; the latter potentially necessitating surgical intervention. Endobronchial histoplasmosis should be considered in the differential diagnosis of obstructing endobronchial lesions associated with hemoptysis, especially when prior and(or) concurrent biopsies fail to disclose malignancy.

Isolated gastrointestinal histoplasmosis: case report and review of the literature

The usual manifestation of histoplasmosis is in the form of respiratory illness. We report the case of a 67-year-old man who presented with chronic diarrhea and did not respond to the conventional treatment, including that for Clostridium difficile. He was found to have isolated colonic histoplasmosis infection, which was treated with itraconazole. There was no evidence of any disseminated disease. His only immunocompromised state was end-stage renal disease, for which he was on chronic hemodialysis. Although it is well documented as a part of disseminated histoplasmosis, our extensive review of the literature did not reveal any reported case of isolated colonic histoplasmosis in a patient on hemodialysis.

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.

Diagnosis of histoplasmosis by antigen detection based upon experience at the histoplasmosis reference laboratory

Histoplasmosis is a common infection in endemic regions of North and Latin America, causing a broad spectrum of clinical findings. The diagnosis may be missed or delayed because histoplasmosis is not considered in the differential. A battery of serologic and mycologic tests may be used for the diagnosis, but each has advantages and limitations. Antigen detection may be particularly helpful for making a rapid diagnosis in patients with more extensive infection. The purpose of this review is to provide a comprehensive discussion of the role of antigen detection in the diagnosis of histoplasmosis, to provide the clinician and laboratory worker with a fuller understanding of the benefits and limitations of this useful laboratory method. This report is based soley upon the experience at the Histoplasmosis Reference Laboratory, and can not be used in interpretation of results of Histoplasma antigen testing done at other laboratories.

Redundancy, phylogeny and differential expression of Histoplasma capsulatum catalases

Histoplasma capsulatum produces an extracellular catalase termed M antigen, which is similar to catalase B of Aspergillus and Emericella species. Evidence is presented here for two additional catalase isozymes in H. capsulatum. Catalase A is highly similar to a large-subunit catalase in Aspergillus and Emericella species, while catalase P is a small-subunit catalase protein with greatest similarity to known peroxisomal catalases of animals and Saccharomycotina yeasts. Complete cDNAs for the CATA and CATP genes (encoding catalases A and P, respectively) were isolated. The transcriptional expression of the H. capsulatum CATA, CATB (M antigen) and CATP genes was assessed by Northern blot hybridizations on total RNA. Results at the transcript levels for these genes are shown for three conditions: cell morphology (mycelial versus yeast phase cells), oxidative stress (in response to a challenge with H(2)O(2)) and carbon source (glucose vs glycerol). Collectively, these results demonstrated regulation of CATA by both cell morphology and oxidative stress, but not by carbon source, and regulation of CATB and CATP by carbon source but not cell morphology or oxidative stress. A phylogenetic analysis of presently available catalase sequences and intron residences was done. The results support a model for evolution of eukaryotic monofunctional catalase genes from prokaryotic genes.

Identification of constituents of human neutrophil azurophil granules that mediate fungistasis against Histoplasma capsulatum

Previously we demonstrated that human neutrophils mediate potent and long-lasting fungistasis against Histoplasma capsulatum yeasts and that all of the fungistatic activity resides in the azurophil granules. In the present study, specific azurophil granule constituents with fungistatic activity were identified by incubation with H. capsulatum yeasts for 24 h and by quantifying the subsequent growth of yeasts via the incorporation of [(3)H]leucine. Human neutrophil defensins HNP-1, HNP-2, and HNP-3 inhibited the growth of H. capsulatum yeasts in a concentration-dependent manner with maximum inhibition at 8 microg/ml. At a concentration of 4 microg/ml, all possible paired combinations of defensins exhibited additive fungistatic activity against H. capsulatum yeasts. Cathepsin G and bactericidal-permeability-increasing protein (BPI) also mediated fungistasis against H. capsulatum in a concentration-dependent manner. The fungistatic activities of combinations of cathepsin G and BPI were additive, as were those of combinations of cathepsin G or BPI with HNP-1, HNP-2, and HNP-3. Lysozyme and elastase exhibited modest antifungal activity, and azurocidin and proteinase 3 exhibited no significant fungistasis against H. capsulatum yeasts. Thus, defensins, cathepsin G, and BPI are the major anti-H. capsulatum effector molecules in the azurophil granules of human neutrophils.

Fungal pneumonias. The endemic mycoses

Each year, a vast number of individuals are infected with the endemic fungi. An expanding population, along with further land development in endemic areas, will likely continue to place individuals at risk for exposure to these organisms. A high index of suspicion may be required to diagnose histoplasmosis, blastomycosis, or coccidioidomycosis, particularly for patients who do not reside in endemic areas. Although the majority of patients with histoplasmosis, blastomycosis, and coccidioidomycosis experience self-limited infections, treatment is necessary for patients with severe pneumonitis as well as various forms of chronic pulmonary and disseminated infections. The newer azole agents--itraconazole and fluconazole--are useful in the treatment of these infections and have provided alternatives to long-term therapy with amphotericin B for many patients.

Regulation of the Macrophage Vacuolar ATPase and Phagosome-Lysosome Fusion by Histoplasma capsulatum

Histoplasma capsulatum (Hc) maintains a phagosomal pH of about 6.5. This strategy allows Hc to obtain iron from transferrin, and minimize the activity of macrophage (Mø) lysosomal hydrolases. To determine the mechanism of pH regulation, we evaluated the function of the vacuolar ATPase (V-ATPase) in RAW264.7 Mø infected with Hc yeast or the nonpathogenic yeast Saccharomyces cerevisae (Sc). Incubation of Hc-infected Mø with bafilomycin, an inhibitor of the V-ATPase, did not affect the intracellular growth of Hc, nor did it affect the intraphagosomal pH. In contrast, upon addition of bafilomycin, phagosomes containing Sc rapidly changed their pH from 5 to 7. Hc-containing phagosomes had 5-fold less V-ATPase than Sc-containing phagosomes as quantified by immunoelectron microscopy. Furthermore, Hc-containing phagosomes inhibited phagolysosomal fusion as quantified by the presence of acid phosphatase, accumulation of LAMP2, and fusion with rhodamine B-isothiocyanate-labeled dextran-loaded lysosomes. Finally, in Hc-containing phagosomes, uptake of ferritin was equivalent to phagosomes containing Sc, indicating that Hc-containing phagosomes have full access to the early “bulk flow” endocytic pathway. Thus, Hc yeasts inhibit phagolysosomal fusion, inhibit accumulation of the V-ATPase in the phagosome, and actively acidify the phagosomal pH to 6.5 as part of their strategy to survive in Mø phagosomes.

Modulation of the effector function of human macrophages for Histoplasma capsulatum by HIV-1. Role of the envelope glycoprotein gp120

We have demonstrated that monocyte-derived macrophages (Mphi) from HIV+ individuals are deficient in their capacity to phagocytose Histoplasma capsulatum (Hc) yeasts, and are more permissive for the intracellular growth of Hc. To determine whether these defects in Mphi function were caused by HIV infection of the Mphi and/or by pathological events associated with HIV infection, cultured normal human Mphi were infected with the HIV-1BaL strain. Virus production, quantified by reverse transcriptase activity and p24 antigen, was evident on day 8 after infection and peaked on day 16. On days 12, 16, and 20 after infection, HIV-1-infected Mphi were deficient in their capacity to recognize and bind Hc yeasts compared with control Mphi, and also were more permissive for the intracellular growth of Hc. Culture of normal Mphi with the envelope glycoprotein gp120 inhibited phagocytosis of Hc yeasts by Mphi in a concentration-dependent manner, but did not cause more rapid intracellular growth of Hc. Normal Mphi cultured in the serum of HIV+ individuals with impaired Mphi function subsequently were deficient in their capacity to phagocytose Hc yeasts, and were more permissive for the intracellular growth of yeasts compared with Mphi cultured in normal serum. Conversely, culture of normal Mphi in the serum of HIV+ patients with normal Mphi function did not affect the interaction of Hc yeasts with Mphi. Moreover, when Mphi from HIV+ individuals that were initially defective in host defense against Hc were cultured in normal HIV- serum, normal Mphi function was demonstrated. Adsorption of gp120 from the serum of two HIV+ patients removed the capacity of the serum to cause a Mphi defect in phagocytosis of Hc, but had no effect on the capacity of the serum to cause accelerated intracellular growth. These data demonstrate that observed defects in Mphi interaction with Hc yeasts may be caused by gp120 and other, as yet unknown serum component(s) probably released into serum by HIV-infected cells.

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.

Review of oral histoplasmosis in Malaysians

We reviewed biopsy records for 37 cases of oral histoplasmosis for patient characteristics, clinical features, and histopathologic findings. These represented cases diagnosed in the Division of Stomatology, Institute for Medical Research, Kuala Lumpur between July 1967 and October 1994. All were male patients who ranged in age from 11 to 79 years (mean age, 56.7 years). There were 40.6% Malays, 37.8% Chinese, 18.9% Indians, and 2.7% other races. Five patients with mouth lesions as the initial presenting lesions were proven to be cases of disseminated histoplasmosis. In the remaining cases apart from the biopsy-proven oral histoplasmosis lesions, the extent of the disease elsewhere was unknown. The majority of these lesions involved the gingiva, tongue, and palate in decreasing order of frequency. The most frequent presenting symptom was oral mucosal ulceration. Squamous cell carcinoma and tuberculosis were the two most common clinical differential diagnoses. Our present findings compare favorably with published reports from other regions.

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.

Pharmacotherapy of disseminated histoplasmosis in patients with AIDS

OBJECTIVE

To review the pharmacotherapy of disseminated histoplasmosis (DH) in patients with AIDS. The article provides an overview of the pathophysiology, epidemiology, clinical presentation and diagnosis of this disease. Clinical trials reporting intervention with antifungal therapy are reviewed, with an emphasis on efficacy and toxicity of these agents.

DATA SOURCES

A MEDLINE search from 1976 to the present was performed to identify pertinent biomedical literature, including reviews.

STUDY SELECTION

All available reviews and clinical trials in AIDS patients were evaluated, as were all available case series and interventional clinical trials.

DATA SYNTHESIS

DH in patients with HIV infection is an AIDS-defining opportunistic infection caused by Histoplasma capsulatum. It is most frequently observed in HIV-infected patients living in or traveling to endemic regions. The clinical presentation most often includes fever and weight loss, but may be complicated by comorbid illness such as other opportunistic infections. Diagnosis is best established by histologic examination of peripheral blood smear or bone marrow aspirate, or isolation of the organism in cultures of blood, bone marrow, and respiratory secretions. Serologic examinations may provide supportive diagnostic information. Detection of histoplasma polysaccharide antigen (HPA) in serum or urine may prove to be a promising approach for the rapid diagnosis and therapeutic monitoring of DH in AIDS patients. In contrast to immunocompetent hosts, high relapse rates are reported after therapy in AIDS patients. Therefore, initial (induction) therapy is routinely followed by long-term (maintenance) therapy to prevent relapse. Issues regarding the selection, dosage, and duration of therapy, as well as prophylaxis of patients at highest risk, still need to be addressed by controlled clinical trials.

CONCLUSIONS

Amphotericin B is presently the drug of choice for induction therapy. Maintenance therapy with either amphotericin B or an oral azole antifungal agent active against H. capsulatum is necessary to prevent relapse. Itraconazole, a triazole antifungal agent, may provide effective alternative therapy for both induction and maintenance treatment of DH.

Histoplasma variation and adaptive strategies for parasitism: new perspectives on histoplasmosis

This review summarizes the biology of Histoplasma capsulatum in relation to a wide variety of corresponding pathologies in histoplasmosis. Features of these disease syndromes can be explained in part by natural variations within the fungal population and adaptations made by individual organisms to specific environments. H. capsulatum grows as mycelia and conidia in the soil; once inhaled, the organism undergoes a dramatic morphological and physiological conversion to a yeast form. The yeasts proliferate within the phagolysosomes of macrophages, using a variety of specific strategies for intracellular survival. Even avirulent strains or variants are able to avoid being killed by macrophages and instead establish inapparent or persistent infections. The ingested avirulent organisms assume enlarged shapes similar in appearance to those seen in histological sections of tissues from patients with histoplasmosis. Respiratory tract epithelial cells also appear to play a role in persistence: within them yeasts undergo phenotypic switching akin to the phase variation observed in other pathogens. This particular change involves the loss or modification of cell wall alpha-(1,3)-glucan, which is also correlated with the spontaneous appearance of avirulent variants. The repertoire of adaptive responses and natural variations within this species probably evolved from the need to adjust to a wide range of dynamic environments. In combination with the immune status of the host, these characteristics of H. capsulatum appear to influence the epidemiology, extent, and persistence of histoplasmosis.

Panniculitis in an immunocompromised patient

We present a patient in whom histoplasmosis panniculitis developed during steroid therapy for pancytopenia secondary to myelodysplasia. Although the cutaneous manifestations of disseminated histoplasmosis are rare, we review them because of the increasing numbers of organ-transplant patients, as well as other patients with immunodeficiency, including acquired immune deficiency syndrome, in whom the risk of this unusual presentation of histoplasmosis must be considered.

Colonic histoplasmosis in acquired immunodeficiency syndrome. Report of two cases

Colonic histoplasmosis is a rare entity. There have been four previous reported cases within the population of patients with human immunodeficiency virus (HIV) infection. Because of the increasing incidence of HIV infection within regions where histoplasmosis is endemic, this condition may become more common. Gastrointestinal histoplasmosis has protean clinical manifestations, and symptoms are often nonspecific. Any patient with HIV infection who has unexplained GI symptoms should undergo evaluation for possible histoplasmosis. Aggressive long-term amphotericin B therapy has been effective in HIV patients with histoplasmosis. Resection or diversion of symptomatic colonic strictures caused by histoplasmosis may be necessary in addition to medical therapy.

Cutaneous lesions of disseminated histoplasmosis in human immunodeficiency virus-infected patients

Disseminated histoplasmosis is being diagnosed more frequently in persons infected with the human immunodeficiency virus and is often the initial manifestation of the acquired immunodeficiency syndrome (AIDS). Disease-related cutaneous features of HIV-associated disseminated histoplasmosis are defined as mucocutaneous lesions from which fungal organisms were either cultured or demonstrated histopathologically. We report four HIV-seropositive patients with disseminated histoplasmosis who had culture-positive skin or oral lesions of histoplasmosis and review the specific cutaneous manifestations of HIV-associated disseminated histoplasmosis. Including our patients, disease-related skin and/or mucosal lesions were present in 11% of patients (26% of 239) with HIV-associated disseminated histoplasmosis. The possibility of disseminated histoplasmosis should be considered in all HIV-infected persons and in persons with AIDS risk factors who have fever, weight loss, hepatosplenomegaly, and new cutaneous lesions. An early skin or mucosal biopsy specimen for crushed tissue preparation, histologic evaluation, and fungal culture is a simple, rapid diagnostic procedure.