Medical Microbiology

6 FungiasHumanPathogens

PrimaryMycoses

&Primarysystemicmycosesincludehistoplasmosis(Histoplasmacapsula-

tum),NorthAmericanblastomycosis(Blastomycesdermatitidis),coccidioido-

mycosis(Coccidioidesimmitis),andSouthAmericanblastomycosis(Paracoc-

cidioidesbrasiliensis).Thenaturalhabitatofthesepathogensisthesoil.Their

sporesareinhaledwithdust,getintothelungs,andcauseaprimarypulmon-

arymycosis.Startingfromfociinthelungs,theorganismscanthenbetrans-

ported,hematogenouslyorlymphogenously,tootherorgansincludingthe

skin,wheretheycausegranulomatous,purulentinfectionfoci.Laboratorydi-

agnosticsaimatdirectdetectionofthepathogensunderthemicroscopeand

inculturesaswellasidentificationofantibodies.Thetherapeuticsusedto

treattheseinfectionsareamphotericinBandazoles.Alloftheprimarysys-

temicmycosesareendemictocertaingeographicareas,insomecasesquite

limitedinextent.CentralEuropeisnotaffectedbythesediseases.Theyare

notcommunicableamonghumans. &

Histoplasmacapsulatum(Histoplasmosis)

Histoplasmacapsulatumisthepathogenresponsibleforhistoplasmosis,an

intracellularmycosisofthereticuloendothelialsystem.Thesexualstageor

formofthisfungusiscalledEmmonsiellacapsulata.

Morphologyandculture.H.capsulatumisadimorphicfungus.Asaninfec-

tiouspathogeninhumantissuesitalwaysformsyeastcells(Fig.6. 1 ).The

smallindividualcellsareoftenlocalizedinsidemacrophagesandhavea

diameterof 2 – 3 lm.

Giemsaandgramstainingdonot“take”onthecellwallsofH.capsulatum,

forwhichreasonthecellsoftenappeartobesurroundedbyanemptyareola,

whichwasincorrectlytakentobeacapsule,resultinginthedesignationH.

capsulatum.Thisspeciescanbegrownonthenutrientmediumsnormally

usedforfungalcultures.H.capsulatumgrowsasamyceliumintwotothree

weeksonSabouraudagaratatemperatureof 20 – 308 C.

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Kayser, Medical Microbiology © 2005 Thieme