Pulmonary Histoplasmosis

Disseminated Histoplasmosis Presenting as Obstructive Jaundice

Gastrointestinal manifestations in systemic fungal infection are not uncommon; however, obstructive jaundice due to lymphadenopathy is considered rare. We present a case of a 16-year-old male patient who presented with painless jaundice. Laboratory tests revealed direct hyperbilirubinemia with cholestatic liver injury. Chest and abdominal computed tomography showed mediastinal and porta hepatis lymphadenopathy, with severe biliary ductal dilatation proximal to an obstructing lymph node near the head of the pancreas. Endoscopic ultrasound showed a 22 × 35-mm lymph node with a mass effect on the common bile duct leading to obstructive jaundice. Infectious workup confirmed the diagnosis of disseminated histoplasmosis.

A Case of Hemophagocytic Lymphohistiocytosis Secondary to Disseminated Histoplasmosis

Hemophagocytic lymphohistiocytosis (HLH) is a rare condition characterized by a pathologic immune dysregulation resulting in extreme inflammation. Clinical manifestations are varied but can include severe multiorgan failure and death. HLH has been associated with malignancies, autoimmune diseases, and infections, such as histoplasmosis. Histoplasmosis commonly has subclinical manifestations but can also present in its disseminated form. We present the case of an immunocompromised patient with worsening liver function caused by hepatic histoplasmosis that later triggered HLH with severe multiorgan dysfunction.

Disseminated Histoplasmosis and Secondary Hemophagocytic Syndrome in a Non-HIV Patient

Histoplasma duboisii, a variant of Histoplasma capsulatum that causes “African histoplasmosis,” can be resistant to itraconazole, requiring intravenous amphotericin B treatment. Rarely, these patients do not respond to intravenous antifungal therapy, and in such cases, patients may progress to develop secondary hemophagocytic lymphohistiocytosis (HLH). We present a case of a 34-year-old male patient with sickle cell disease who presented with a 5-month history of an enlarging painless axillary mass, persistent low grade fevers, night sweats, weight loss, and anorexia. An excisional biopsy of the right axillary lymph node revealed yeast and granulomas consistent with histoplasma infection. He was started on oral itraconazole. After 4 weeks of therapy, laboratory evaluation revealed worsening anemia, thrombocytopenia, and transaminitis. Due to failure of oral therapy, he was admitted for intravenous amphotericin B treatment. During his hospital course anemia, thrombocytopenia, and transaminitis all worsened. A bone marrow biopsy was done that was consistent with HLH. His clinical status continued to deteriorate, developing multiorgan failure and disseminated intravascular coagulation. He unfortunately had a cardiorespiratory arrest after eight days of admission and passed away.

Extracellular superoxide dismutase protects Histoplasma yeast cells from host-derived oxidative stress

In order to establish infections within the mammalian host, pathogens must protect themselves against toxic reactive oxygen species produced by phagocytes of the immune system. The fungal pathogen Histoplasma capsulatum infects both neutrophils and macrophages but the mechanisms enabling Histoplasma yeasts to survive in these phagocytes have not been fully elucidated. We show that Histoplasma yeasts produce a superoxide dismutase (Sod3) and direct it to the extracellular environment via N-terminal and C-terminal signals which promote its secretion and association with the yeast cell surface. This localization permits Sod3 to protect yeasts specifically from exogenous superoxide whereas amelioration of endogenous reactive oxygen depends on intracellular dismutases such as Sod1. While infection of resting macrophages by Histoplasma does not stimulate the phagocyte oxidative burst, interaction with polymorphonuclear leukocytes (PMNs) and cytokine-activated macrophages triggers production of reactive oxygen species (ROS). Histoplasma yeasts producing Sod3 survive co-incubation with these phagocytes but yeasts lacking Sod3 are rapidly eliminated through oxidative killing similar to the effect of phagocytes on Candida albicans yeasts. The protection provided by Sod3 against host-derived ROS extends in vivo. Without Sod3, Histoplasma yeasts are attenuated in their ability to establish respiratory infections and are rapidly cleared with the onset of adaptive immunity. The virulence of Sod3-deficient yeasts is restored in murine hosts unable to produce superoxide due to loss of the NADPH-oxidase function. These results demonstrate that phagocyte-produced ROS contributes to the immune response to Histoplasma and that Sod3 facilitates Histoplasma pathogenesis by detoxifying host-derived reactive oxygen thereby enabling Histoplasma survival.

Histoplasma capsulatum is a fungal pathogen that is endemic to the Mississippi and Ohio River valleys. An estimated 200,000 infections occur annually in the United States. Histoplasma is adept at surviving within both neutrophils and macrophages, which normally kill fungal cells by producing reactive oxygen molecules that are toxic to microbes. In this study, we demonstrate the role of a superoxide dismutase enzyme (Sod3) produced by Histoplasma cells and we show that it enables Histoplasma to survive these reactive oxidative molecules produced by the host. We show that Histoplasma directs the Sod3 protein to the surface of yeast cells and into the extracellular environment, positioning it to destroy extracellular superoxide produced by neutrophils and macrophages. Our results highlight the importance of reactive oxygen produced by immune cells and define the mechanism by which Histoplasma survives these immune defenses and establishes infections in its host.

Respiratory infections in immunocompromised patients

PURPOSE OF REVIEW

Immunosuppressive states and therapies are becoming common in clinical practice. Recent advances and trends in bacterial, fungal, viral and parasitic pulmonary infections in immunosuppressed patients are described.

RECENT FINDINGS

Pulmonary infections can jeopardize the prognosis of immunosuppressed patients. The number of patients infected with multidrug-resistant bacteria or opportunistic pathogens like rapid-growing environmental mycobacteria, Strongyloides stercoralis or Rhodococcus equi is increasing with the increased numbers of immunosuppressed patients due to HIV/AIDS and the potent immunosuppressive therapies used in solid-organ and haematopoietic transplantations, cancer and systemic illnesses. The slow development of more effective antibiotics underlines the necessity of preventive measures, development of rapid detection tests for pathogens and appropriate treatment regimens to avoid development of further resistance.

SUMMARY

Adequate prophylaxis, clinical suspicion, microbiological and molecular investigations, drug susceptibility-based antibiotic treatment and new drug development are strategies required to face up to the challenge of pulmonary infections in immunodepressed patients.

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.

Molecular evidence of recurrent histoplasmosis with 9-year latency in a patient with Addison's disease

We present a case of fatal histoplasmosis in a patient with Addison's disease and long-term use of corticosteroid. The patient acquired Histoplasma capsulatum in China and initially presented with a laryngeal mass. He developed fulminant pneumonia and respiratory failure 9 years later. Nucleotide sequences of internal transcribed spacer regions of rRNA genes of the H. capsulatum isolate recovered from biopsied lung tissue and of the extracted fungal DNA from the laryngeal lesion were identical, indicating the recurrent nature of infection.

Mediastinal histoplasmosis: report of the first two Brazilian cases of mediastinal granuloma

This report documents the first two Brazilian cases of mediastinal granuloma due to histoplasmosis, presenting selected aspects on the diagnosis. Tissue samples revealing histoplasmosis were obtained from each of the patients by mediastinoscopy and thoracotomy. In the second patient, a subcarinal calcified mass eroded into the bronchial tree, leading to secondary bilateral aspiration pneumonitis one week after thoracotomy. Although rare, histoplasmosis should be included in the differential diagnosis of mediastinal granuloma, specially if there are calcifications greater than 10 mm in dimension.