Bruce S. Klein

Isolation of Blastomyces dermatitidis in Soil Associated with a Large Outbreak of Blastomycosis in Wisconsin

In investigating six cases of blastomycosis in two school groups that had separately visited an environmental camp in northern Wisconsin in June 1984, we identified a large outbreak of the disease and isolated Blastomyces dermatitidis from soil at a beaver pond near the camp. Of 89 elementary-school children and 10 adults from the two groups, 48 (51 percent) of the 95 evaluated in September had blastomycosis. Of the cases, 26 (54 percent) were symptomatic (the median incubation period was 45 days; range, 21 to 106 days). No cases were identified in 10 groups that visited the camp two weeks before or after these two groups. A review of camp itineraries, a questionnaire survey, and environmental investigation showed that blastomycosis occurred in two of four groups that visited a beaver pond and in none of eight groups that did not. Walking on the beaver lodge (P = 0.008) and picking up items from its soil (P = 0.05) were associated with illness. Cultures of soil from the beaver lodge and decomposed wood near the beaver dam yielded B. dermatitidis. We conclude that B. dermatitidis in the soil can be a reservoir for human infection.

Advances in combating fungal diseases: vaccines on the threshold

The dramatic increase in fungal diseases in recent years can be attributed to the increased aggressiveness of medical therapy and other human activities. Immunosuppressed patients are at risk of contracting fungal diseases in healthcare settings and from natural environments. Increased prescribing of antifungals has led to the emergence of resistant fungi, resulting in treatment challenges. These concerns, together with the elucidation of the mechanisms of protective immunity against fungal diseases, have renewed interest in the development of vaccines against the mycoses. Most research has used murine models of human disease and, as we review in this article, the knowledge gained from these studies has advanced to the point where the development of vaccines targeting human fungal pathogens is now a realistic and achievable goal.

Reduction of Nosocomial Infection during Pediatric Intensive Care by Protective Isolation

To determine whether simple protective isolation reduces the incidence of nosocomial bacterial and fungal infection during pediatric intensive care, we randomly assigned 70 children who were not immuno-suppressed and who required mechanical ventilatory support and three or more days of intensive care to receive standard care (n = 38) or protective isolation (n = 32) with use of disposable, non-waven, polypropylene gowns and nonsterile latex gloves. Risk factors predisposing patients to infection were comparable in the two groups. Nosocomial colonization occurred later among isolated patients (median, vs. 7 days; P less than 0.01) and was associated with subsequent infection in 12 patients, as compared with 12 patients given standard care (P = 0.01). Among patients who were isolated, the interval before the first infection was significantly longer than (median, 20 vs. 8 days; P = 0.04), the daily infection rate was 2.2 times lower than (95 percent confidence interval, 1.2 to 4.0; P = 0.007), and there were fewer days with fewer (13 percent vs. 21 percent; P = 0.001). The benefit of isolation was most notable after seven days of intensive care. Isolation was well tolerated by patients and their families. Regular monitoring showed that the children in each group were touched and handled comparably often by hospital personnel and family members. We conclude that the use of disposable, high-barrier gowns and gloves for the care of selected, high-risk children who require prolonged intensive care significantly reduces the incidence of nosocomial infection, is well tolerated, and does not compromise the delivery of care.

Vaccine-induced protection against 3 systemic mycoses endemic to North America requires Th17 cells in mice

Worldwide rates of systemic fungal infections, including three of the major pathogens responsible for such infections in North America (Coccidioides posadasii, Histoplasma capsulatum, and Blastomyces dermatitidis), have soared recently, spurring interest in developing vaccines. The development of Th1 cells is believed to be crucial for protective immunity against pathogenic fungi, whereas the role of Th17 cells is vigorously debated. In models of primary fungal infection, some studies have shown that Th17 cells mediate resistance, while others have shown that they promote disease pathology. Here, we have shown that Th1 immunity is dispensable and that fungus-specific Th17 cells are sufficient for vaccine-induced protection against lethal pulmonary infection with B. dermatitidis in mice. Further, vaccine-induced Th17 cells were necessary and sufficient to protect against the three major systemic mycoses in North America. Mechanistically, Th17 cells engendered protection by recruiting and activating neutrophils and macrophages to the alveolar space, while the induction of Th17 cells and acquisition of vaccine immunity unexpectedly required the adapter molecule Myd88 but not the fungal pathogen recognition receptor Dectin-1. These data suggest that human vaccines against systemic fungal infections should be designed to induce Th17 cells if they are to be effective.

Vaccine Immunity to Pathogenic Fungi Overcomes the Requirement for CD4 Help in Exogenous Antigen Presentation to CD8+ T Cells Implications for Vaccine Development in Immune-deficient Hosts

Systemic fungal infections with primary and opportunistic pathogens have become increasingly common and represent a growing health menace in patients with AIDS and other immune deficiencies. T lymphocyte immunity, in particular the CD4+ Th 1 cells, is considered the main defense against these pathogens, and their absence is associated with increased susceptibility. It would seem illogical then to propose vaccinating these vulnerable patients against fungal infections. We report here that CD4+ T cells are dispensable for vaccine-induced resistance against experimental fungal pulmonary infections with two agents, Blastomyces dermatitidis an extracellular pathogen, and Histoplasma capsulatum a facultative intracellular pathogen. In the absence of T helper cells, exogenous fungal antigens activated memory CD8+ cells in a major histocompatibility complex class I–restricted manner and CD8+ T cell–derived cytokines tumor necrosis factor α, interferon γ, and granulocyte/macrophage colony-stimulating factor–mediated durable vaccine immunity. CD8+ T cells could also rely on alternate mechanisms for robust vaccine immunity, in the absence of some of these factors. Our results demonstrate an unexpected plasticity of immunity in compromised hosts at both the cellular and molecular level and point to the feasibility of developing vaccines against invasive fungal infections in patients with severe immune deficiencies, including those with few or no CD4+ T cells.

Adaptive Immunity to Fungi

Only a handful of the more than 100,000 fungal species on our planet cause disease in humans, yet the number of life-threatening fungal infections in patients has recently skyrocketed as a result of advances in medical care that often suppress immunity intensely. This emerging crisis has created pressing needs to clarify immune defense mechanisms against fungi, with the ultimate goal of therapeutic applications. Herein, we describe recent insights in understanding the mammalian immune defenses deployed against pathogenic fungi. The review focuses on adaptive immune responses to the major medically important fungi and emphasizes how dendritic cells and subsets in various anatomic compartments respond to fungi, recognize their molecular patterns, and signal responses that nurture and shape the differentiation of T cell subsets and B cells. Also emphasized is how the latter deploy effector and regulatory mechanisms that eliminate these nasty invaders while also constraining collateral damage to vital tissue.

The role of respiratory syncytial virus and other viral pathogens in acute otitis media

We utilized recently developed enzyme immunoassay techniques to examine the role of selected viruses in the etiology of acute otitis media. Viral pathogens were found in middle ear fluids obtained from 13 (24%) of 53 children with acute otitis media; respiratory syncytial virus accounted for ten of the 13 viral agents identified. In addition, respiratory syncytial viral antigen was found in nasopharyngeal washings obtained from 15 of the 53 children. Seven of these children had RSV identified as the sole middle ear pathogen, whereas six children had otitis caused by Streptococcus pneumoniae as either the sole middle ear pathogen or in combination with RSV. Similarly, all three children with respiratory infections caused by influenza virus had ear infections caused by bacterial pathogens, either alone or in combination with influenza virus. These findings suggest that, in patients with viral respiratory infection, coexisting acute otitis media may be associated with the recovery of either viruses or bacteria from the middle ear exudates.

Isolation, purification, and radiolabeling of a novel 120-kD surface protein on Blastomyces dermatitidis yeasts to detect antibody in infected patients.

No well-defined Blastomyces-specific antigens are currently available. We used sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting to identify immunologically active molecules in the cell wall of B. dermatitidis. A major immunoreactive 120-kD protein (WI-1) was present in all five strains studied and comprised 5% of the protein in the cell wall extract obtained after freezing and thawing yeast cells. WI-1 was recognized by serum from all 10 patients with blastomycosis but by none of those from 5 patients with histoplasmosis. It was purified by electroelution, radiolabeled with 125I, and incorporated into a radioimmunoassay (RIA) for serodiagnosis of blastomycosis. Antibody to WI-1 was detected in 58 (85%) of 68 patients with blastomycosis (geometric mean titer, 1:2,981), in two (3%) of 73 patients with histoplasmosis, coccidioidomycosis, sporotrichosis, or candidiasis (titers, 1:86 and 1:91) and in none of 44 healthy persons. WI-1 was shown to be a surface molecule abundant on B. dermatitidis yeasts that were indirectly stained with serum from a rabbit immunized with WI-1. Approximately 0.93 pg of WI-1 or 4.7 x 10(6) WI-1 molecules were found on the surface of an individual yeast using an antigen-inhibition RIA; none was found on Histoplasma capsulatum or Candida albicans yeasts. We conclude that WI-1 is a novel, immunologically active surface molecule on the invasive form of B. dermatitidis and that WI-1 can be used to reliably detect antibody and study the immunopathogenesis of blastomycosis.

Linking fungal morphogenesis with virulence

Pathogenic fungi have become an increasingly common cause of systemic disease in healthy people and those with impaired immune systems. Although a vast number of fungal species inhabit our planet, just a small number are pathogens, and one feature that links many of them is the ability to differentiate morphologically from mould to yeast, or yeast to mould. Morphological differentiation between yeast and mould forms has commanded attention for its putative impact on the pathogenesis of invasive fungal infections. This review explores the current body of evidence linking fungal morphogenesis and virulence. The topics addressed cover work on phase‐locked fungal cells, expression of phase‐specific virulence traits and modulation of host responses by fungal morphotypes. The effect of morphological differentiation on fungal interaction with host cells, immune modulation and the net consequence on pathogenesis of disease in animal model systems are considered. The evidence argues strongly that morphological differentiation plays a vital role in the pathogenesis of fungal infection, suggesting that factors associated with this conversion process represent promising therapeutic targets.

Blastomycosis in solid organ transplant recipients

Abstract: 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.