Chapter 231 Blastomycosis (Blastomyces dermatitidis) Gregory M. Gauthier, Bruce S. Klein Etiology Blastomyces dermatitidis belongs to a group of fungi that exhibit thermal dimorphism. In the soil, these fungi grow as mold and produce spores, which are the infectious particles. When inhaled into the lungs, the spores convert into pathogenic yeast and cause infection. Epidemiology B. dermatitidis causes disease in immunocompetent and immunocompromised children. Only 2-13% of blastomycosis cases occur in patients <18 yr of age. Neonatal blastomycosis is rare and can be transmitted through the placenta to the fetus. In North America, the geographic distribution of blastomycosis cases is restricted to the Midwest, south-central, and southeastern USA and parts of Canada bordering the Great Lakes and Saint Lawrence River Valley. Infections have also been reported from Africa, India, the Middle East, and Central and South America. B. dermatitidis grows in sandy soils that have decaying vegetation and are near water. Most infections with B. dermatitidis are sporadic; however, outbreaks have been well described. The severity of infection is influenced by the size of the inhaled inoculum and the integrity of the patient’s immune system. Pathogenesis The ability to convert from spores to yeast in the lung is a crucial event in the pathogenesis of infection with B. dermatitidis and other dimorphic fungi. This phase transition enables B. dermatitidis to evade the host immune system and establish infection. In the yeast form, B. dermatitidis produces BAD-1 (Blastomyces adhesin-1; formerly WI-1), an essential virulence factor that is displayed on the cell wall and secreted. BAD-1 promotes binding of yeast to macrophages in lung alveoli, blocks the deposition of complement on the yeast surface, binds calcium, and suppresses the production of pro-inflammatory cytokines in the host. The phase transition from mold to yeast is a complex event that involves alteration in cell wall composition, metabolism, intracellular signaling, and gene expression. In B. dermatitidis, this transition is regulated, in part, by a histidine kinase known as DRK1 (dimorphism regulating kinase-1). This sensor kinase controls not only the conversion of mold to yeast but also spore production, cell wall composition, and BAD-1 expression; the loss of DRK1 expression through gene disruption renders B. dermatitidis avirulent in a murine model of blastomycosis. Clinical Manifestations The clinical manifestations of blastomycosis are heterogeneous and include subclinical infection, symptomatic pneumonia, and disseminated disease. Clinical disease develops 3 wk to 3 mo following exposure to B. dermatitidis. Asymptomatic or subclinical infections are estimated to occur in 50% of patients. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Rumination, Pica, and Elimination (Enuresis, Encopresis) Disorders Adolescent Pregnancy Neisseria gonorrhoeae (Gonococcus) Fever without a Focus Stay updated, free articles. Join our Telegram channel Join Tags: Nelson Textbook of Pediatrics Expert Consult Jun 18, 2016 | Posted by admin in PEDIATRICS | Comments Off on Blastomycosis (Blastomyces dermatitidis) Full access? Get Clinical Tree
Chapter 231 Blastomycosis (Blastomyces dermatitidis) Gregory M. Gauthier, Bruce S. Klein Etiology Blastomyces dermatitidis belongs to a group of fungi that exhibit thermal dimorphism. In the soil, these fungi grow as mold and produce spores, which are the infectious particles. When inhaled into the lungs, the spores convert into pathogenic yeast and cause infection. Epidemiology B. dermatitidis causes disease in immunocompetent and immunocompromised children. Only 2-13% of blastomycosis cases occur in patients <18 yr of age. Neonatal blastomycosis is rare and can be transmitted through the placenta to the fetus. In North America, the geographic distribution of blastomycosis cases is restricted to the Midwest, south-central, and southeastern USA and parts of Canada bordering the Great Lakes and Saint Lawrence River Valley. Infections have also been reported from Africa, India, the Middle East, and Central and South America. B. dermatitidis grows in sandy soils that have decaying vegetation and are near water. Most infections with B. dermatitidis are sporadic; however, outbreaks have been well described. The severity of infection is influenced by the size of the inhaled inoculum and the integrity of the patient’s immune system. Pathogenesis The ability to convert from spores to yeast in the lung is a crucial event in the pathogenesis of infection with B. dermatitidis and other dimorphic fungi. This phase transition enables B. dermatitidis to evade the host immune system and establish infection. In the yeast form, B. dermatitidis produces BAD-1 (Blastomyces adhesin-1; formerly WI-1), an essential virulence factor that is displayed on the cell wall and secreted. BAD-1 promotes binding of yeast to macrophages in lung alveoli, blocks the deposition of complement on the yeast surface, binds calcium, and suppresses the production of pro-inflammatory cytokines in the host. The phase transition from mold to yeast is a complex event that involves alteration in cell wall composition, metabolism, intracellular signaling, and gene expression. In B. dermatitidis, this transition is regulated, in part, by a histidine kinase known as DRK1 (dimorphism regulating kinase-1). This sensor kinase controls not only the conversion of mold to yeast but also spore production, cell wall composition, and BAD-1 expression; the loss of DRK1 expression through gene disruption renders B. dermatitidis avirulent in a murine model of blastomycosis. Clinical Manifestations The clinical manifestations of blastomycosis are heterogeneous and include subclinical infection, symptomatic pneumonia, and disseminated disease. Clinical disease develops 3 wk to 3 mo following exposure to B. dermatitidis. Asymptomatic or subclinical infections are estimated to occur in 50% of patients. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Rumination, Pica, and Elimination (Enuresis, Encopresis) Disorders Adolescent Pregnancy Neisseria gonorrhoeae (Gonococcus) Fever without a Focus Stay updated, free articles. Join our Telegram channel Join Tags: Nelson Textbook of Pediatrics Expert Consult Jun 18, 2016 | Posted by admin in PEDIATRICS | Comments Off on Blastomycosis (Blastomyces dermatitidis) Full access? Get Clinical Tree
