Blastomycosis-Some Progress but Still Much to Learn

Abstract

Blastomycosis, caused by Blastomyces spp., is an endemic mycosis capable of causing significant disease throughout the body. Higher rates of infection are seen in the Mississippi and Ohio River valleys, the Great Lakes region of the United States and Canada, much of Africa, and, to a lesser extent, in India and the Middle East. Limited reporting inhibits our true understanding of the geographic distribution of blastomycosis. An estimated 50% of those infected remain asymptomatic. Of those who present with symptomatic disease, pulmonary involvement is most common, while the most common extrapulmonary sites are the skin, bones, genitourinary system, and central nervous system. Itraconazole is the standard therapy for mild-moderate disease. Data for other azoles are limited. Amphotericin is used for severe disease, and corticosteroids are occasionally used in severe disease, but evidence for this practice is limited. Despite increasing incidence and geographic reach in recent years, there are still significant knowledge gaps in our understanding of blastomycosis. Here, we provide an updated review of the epidemiology, clinical presentations, and diagnostic and therapeutic approaches for this infection. We also discuss areas needing further research.

Keywords: Blastomyces; Blastomyces dermatitidis; blastomycosis; diseases; fungus; mycosis.

Figure 1

Map of the estimated distribution of Blastomyces. Figure used with permission from Ashraf et al. [5].

Figure 2

Pulmonary blastomycosis chest X-ray image. Chest X-ray seen in a patient with pulmonary blastomycosis demonstrating a right lower lobe consolidation and bilateral military nodules. Image sourced from Sarkar et al. under a creative commons license (CC BY 3.0) [56].

Figure 3

Sites of disseminated blastomycosis. CNS: central nervous system.

Figure 4

Cutaneous blastomycosis. (A) Verrucous blastomycosis; (B) nodular cutaneous blastomycosis with bulla formation; (C) keloidal blastomycosis. All images were obtained through the CDC Public Health Image Library (https://phil.cdc.gov (accessed on 1 August 2022)).

Figure 5

Characteristic Blastomyces microscopy. Hematoxylin and eosin staining of a Blastomyces-containing cerebellar mass at ×400 magnification (A) with large, round, thick-walled yeast cells. Grocott’s methenamine-silver-stained section of the same mass at ×400 magnification (B) with broad-based budding yeast cells. Image source is Kochar et al., 2016, used under a creative commons license (CC BY-NC-SA 3.0) [92].