Medical Microbiology

Blastomycesdermatitidis

(NorthAmericanBlastomycosis)

Blastomycesdermatitidisisadimorphicfungusthatcausesachronicgranu-

lomatousinfection.Thepathogensoccurnaturallyinthesoilandaretrans-

mittedtohumansbyinhalation.

Theprimaryblastomycosisinfectionispulmonary.Secondaryhemato-

genousspreadcanleadtoinvolvementofotherorgansincludingtheskin.

Laboratorydiagnosticmethodsincludemicroscopyandculturingtoidentify

thefungusinsputum,skinlesionpus,orbiopsymaterial.Antibodydetection

usingthecomplementfixationtestoragargelprecipitationisoflimiteddi-

agnosticvalue.AmphotericinBisthetherapeuticagentofchoice.Untreated

blastomycosesalmostalwayshavealethaloutcome.

BlastomycosisoccursmainlyintheMississippiValleyaswellasinthe

easternandnorthernUSA.Infectionsarealsorelativelyfrequentinanimals,

especiallydogs.Susceptiblepersonscannot,however,beinfectedbyinfected

animalsorhumans.Therearenoprophylacticmeasures.

Paracoccidioidesbrasiliensis

(SouthAmericanBlastomycosis)

Paracoccidioidesbrasiliensis(syn.Blastomycesbrasiliensis)isadimorphicfun-

gusthat,inlivingtissues,producesthick-walledyeastcellsof 10 – 30 lmin

diameter,mostofwhichhaveseveralbuds.Whencultivated(25 8 C),thefun-

gusgrowsinthemycelialform.

ThenaturalhabitatofP.brasiliensisisprobablythesoil.Humaninfections

arecausedbyinhalationofspore-ladendust.Primarypurulentand/orgran-

ulomatousinfectionfociarefoundinthelung.Startingfromthesefoci,the

funguscandisseminatehematogenouslyorlymphogenouslyintotheskin,

mucosa,orlymphoidorgans.Adisseminatedparacoccidioidomycosispro-

gressesgraduallyandendslethallyunlesstreated.Thetherapeuticagents

ofchoiceareazolederivatives(e.g.,itraconazole),amphotericinB,andsulfon-

amides.Therapycanpreventthediseasefromprogressing,althoughno

casesareknowninwhichthediseaseiseliminatedoverthelongerterm.

Laboratorydiagnosticsarebasedondetectionofthepathogenunderthe

microscopeandinculturesaswell asonantibody detectionwiththe

complementfixationtestorgelprecipitation.

Paracoccidioidomycosisisobservedmainlyamongfarmersinruralparts

ofSouthAmerica.

PrimaryMycoses 361

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Kayser, Medical Microbiology © 2005 Thieme