The effect of canine macrophages on the adherence and growth of Blastomyces dermatitidis yeast: evidence of a soluble factor that enhances the growth of B. dermatitidis yeast

25-Hydroxyvitamin D concentrations in dogs with naturally acquired blastomycosis

Background

Hypovitaminosis D is common in humans with tuberculosis, and adequate serum 25‐hydroxyvitamin D [25(OH)D] concentrations may improve response to therapy. The pathomechanism of Blastomyces dermatitidis is similar to that of Mycobacterium tuberculosis, but the 25(OH)D status of dogs with blastomycosis has not been investigated.

Objectives

To determine if dogs with blastomycosis have lower 25(OH)D concentrations compared with healthy controls and to explore the prognostic value of 25(OH)D concentrations in blastomycosis.

Animals

35 control dogs (16 client‐owned, healthy dogs and 19 healthy, random‐source hound mixes) and 22 dogs with blastomycosis.

Methods

Prospective study. Serum concentrations of 25(OH)D, parathyroid hormone (PTH), ionized calcium were measured, and biochemistry and hematology profiles were performed. The 25‐hydroxyvitamin D concentrations were compared between groups, and factors associated with 25(OH)D variation were investigated in dogs with blastomycosis. Dogs with blastomycosis were followed for up to 5 years after discharge and factors associated with survival were investigated.

Results

Dogs with blastomycosis had significantly lower concentrations of 25(OH)D and PTH and higher concentrations of ionized calcium than did control dogs. In dogs with blastomycosis, 25(OH)D concentrations were independently associated with neutrophil count, pCO₂, and with bone and skin involvement. The 25‐hydroxyvitamin D concentration was not associated with survival in dogs with blastomycosis, whereas lactate concentrations; bone, skin, and lymph node involvement; number of affected sites; and, presence of respiratory signs were associated with survival.

Conclusions and Clinical Importance

Dogs with blastomycosis had lower 25(OH)D concentrations than did healthy controls. Despite no impact on survival, investigating the effect of 25(OH)D supplementation on recovery is warranted.

Epidemiology, Diagnosis, and Treatment of Blastomycosis in Dogs and Cats

Blastomycosis is one of the most common systemic fungal diseases in dogs in North America, but it is rarely diagnosed in cats. The typical route of infection is inhalation of aerosolized conidia of Blastomyces dermatitidis. From the respiratory tract, the developing yeast form may disseminate throughout the body and affect multiple organ systems, most commonly the lymphatic, skeletal and central nervous systems, eyes and skin. Disseminated disease often is associated with nonspecific signs of illness including lethargy, inappetence and fever, as well as signs referable to specific organ systems like chronic cough and dyspnea, peripheral lymphadenopathy, endophthalmitis, and central nervous signs. Diagnosis is typically made by detection of Blastomyces dermatitidis yeast in affected tissues by fine-needle aspiration cytology or histopathology. The treatment of choice is itraconazole. Prognosis is fair in dogs without central nervous disease and guarded in cats.

Extracellular calcium and magnesium, but not iron, are needed for optimal growth of Blastomyces dermatitidis yeast form cells in vitro

In the present study, we demonstrate that the yeast form of Blastomyces dermatitidis can proliferate for short periods of time in the absence of ferric iron but not in the absence of calcium or magnesium. The results of this study shed light on the resistance of B. dermatitidis to chelating agents, such as deferoxamine, and may explain how B. dermatitidis resists the iron-binding activity of serum transferrin.

Novel role for albumin in innate immunity: serum albumin inhibits the growth of Blastomyces dermatitidis yeast form in vitro

In this study we found that serum inhibitory activity against Blastomyces dermatitidis was principally mediated by albumin. This was confirmed in experiments using albumin from several mammalian species. Analbuminemic rat serum did not inhibit B. dermatitidis growth in vivo; however, the addition of albumin restored inhibitory activity. Inhibitory activity does not require albumin domain III and appears to involve binding of a low-molecular-weight yeast-derived growth factor.

Molecular genetic analysis of Blastomyces dermatitidis reveals new insights about pathogenic mechanisms

Fungal pathogens have emerged as a public health menace owing to the expanding population of vulnerable patients and to a heightened exposure to fungi in our environment, particularly for the systemic dimorphic fungi that inhabit soil worldwide. A better understanding of these microbes and their pathogenic mechanisms is badly needed to further research into therapeutic options. Advances in the molecular tools for genetic manipulation of Blastomyces dermatitidis have enhanced our ability to study this poorly understood dimorphic fungal pathogen. Recent refinements in gene-transfer technique, new selection markers, reliable reporter fusions and successes in gene targeting have shed light upon the importance of the mycelium-to-yeast transition and the crucial and complex role the BAD1 adhesin plays in pathogenesis.

Transferrin independent serum inhibition of Blastomyces dermatitidis

Human serum has been reported to inhibit the growth of several fungal pathogens. Serum inhibitory activity has predominantly been associated with transferrin-mediated iron binding. We found that serum from several animal species (human, dog, mouse and fetal bovine) inhibited the growth of the dimorphic fungal pathogen, Blastomyces dermatitidisin vitro. In initial studies, we found no correlation between the total iron-binding capacity of various sera and their inhibitory activity against B. dermatitidis yeast. In addition, we were unable to abrogate the inhibitory activity of human serum against B. dermatitidis yeast by the addition of ferric chloride (10-200 microM). We found that apo-transferrin had little or no inhibitory activity against B. dermatitidis yeast. Furthermore, serum from hypotransferrinemic mice (hpx/hpx) had inhibitory activity against B. dermatitidis yeast that was equivalent to that of normal mouse serum. These findings are consistent with our initial findings and suggest that serum inhibitory activity against B. dermatitidis yeast is transferrin independent. Although high concentrations (3.5-5 mg/ml) of lactoferrin did have inhibitory activity against B. dermatitidis yeast, these concentrations were orders of magnitude greater than those found in serum under normal physiological conditions, suggesting that lactoferrin was not likely to contribute to serum inhibitory activity against B. dermatitidis yeast. Our findings suggest that host iron-binding proteins may be relatively ineffective in innate host defense against infection with B. dermatitidis yeast.

Using new genetic tools to study the pathogenesis of Blastomyces dermatitidis

Fungal pathogens have emerged as a public health menace owing to the expanding population of vulnerable patients and a heightened exposure to fungi in our environment, particularly for the systemic dimorphic fungi that inhabit soil worldwide. A better understanding of these invaders and their pathogenic mechanisms is badly needed to further research into therapeutic options. Advances in the molecular tools available for genetic manipulation of Blastomyces dermatitidis have enhanced our ability to study this poorly understood dimorphic fungal pathogen. Recent refinements in gene-transfer techniques, new selection markers, reliable reporter fusions and successes in gene targeting have shed light upon the importance of the mycelium-to-yeast transition and the crucial and complex role the BAD1 adhesin plays in pathogenesis.