Medical Microbiology

Pathogenesisandclinicalpicture.ThenaturalhabitatofH.capsulatumisthe

soil.Spores(conidia)areinhaledintotherespiratorytract,aretakenupby

alveolarmacrophages,andbecomeyeastcellsthatreproducebybudding.

Smallgranulomatousinflammatoryfocidevelop.Thepathogenscandissemi-

natehematogenouslyfromtheseprimaryinfectionfoci.Thereticuloendothe-

lialsystem(RES)ishitparticularlyhard.Lymphadenopathiesdevelopandthe

spleenandliverareaffected.Over 90 %ofinfectionsremainclinicallysilent.

Theclinicalpicturedependsheavilyonanypredisposinghostfactorsandthe

infectivedose.Ahistoplasmosiscanalsorunitscourseasarespiratoryinfec-

tiononly.DisseminatedhistoplasmosesarealsoobservedinAIDSpatients.

Diagnosis.Suitablematerialfordiagnosticanalysisisprovidedbybronchial

secretion,urine,orscrapingsfrominfectionfoci.Formicroscopicexamina-

tion,GiemsaorWrightstainingisappliedandyeastcellsarelookedforinside

themacrophagesandpolymorphonuclearleukocytes.Culturesonbloodor

Sabouraudagarmustbeincubatedforseveralweeks.Antibodiesaredetected

usingthecomplementfixationtestandagargelprecipitation.Thediagnostic

valueofpositiveornegativefindingsinahistoplasminscratchtestisdoubt-

ful.

Therapy.TreatmentwithamphotericinBisonlyindicatedinsevereinfec-

tions,especiallythedisseminatedform.

Epidemiologyandprevention.Histoplasmosisisendemictothemidwestern

USA,CentralandSouthAmerica,Indonesia,andAfrica.Withfewexceptions,

PrimaryMycoses 359

Histoplasmacapsulatum

a b c

Fig.6. 1 aYeastcellsinmacrophage.

bMacroconidia(7– 15 lm).

cMicroconidia(2– 5 lm).

6

Kayser, Medical Microbiology © 2005 Thieme