Medical Microbiology

552 10 Helminths

tosomafemales.Alargeproportion(upto 50 %)oftheeggslaidremainin

humanbodytissues,notonlyneartheworms(urinarybladder,intestine),

butalso inmoredistantlocalizationsduetohematogenous spreading

(mainlytotheliverandlungs,morerarelytotheCNS,theskin,andother

organs),wheretheylodgeinsmallvessels.

Themiracidia,whichremainviableforaboutthreeweeks,produceantigens

(proteins,glycoproteins),whicharesecretedthroughtheeggshellintothe

tissueandarestillpresentintheeggaftertheciliatedlarvahasdiedoff.After

antigenicstimulationofTlymphocytessecretedcytokinescontributetopro-

ducegranulomatousreactionfoci(so-called“pseudotubercles”):aboveall

macrophages,neutrophilicandeosinophilicgranulocytes,aswellasfibro-

blasts,aggregatearoundsingleeggsoranumberofcentrallylocatedeggs

(Fig. 1 0. 5 ).Thesefocimaymergeandformastartingpointforlarger,gran-

ulomatousproliferationsthatprotrudeintothelumenoftheurinarybladder

orintestine.Theeggsinthetissuesdieoffwithinaboutthreeweeksandare

eitherbrokendownortheycalcify.Thegranulomasarereplacedbyconnec-

tivetissue,producingmoreandmorefibrouschangesandscarring.

Themainformsofschistosomosisaredifferentiatedaccordingtothe

localizationofthelesions:

&Urinaryschistosomosis(urinarybilharziosis).Causativeagent:S.hema-

tobium.Incubation 10 – 12 weeksorlonger,morbidityrateashighas 50 – 70 %.

Hematuria(mainlyinthefinalportionofurine),micturitiondiscomfort,

hyperemia,increasingfibrosis, 1 – 2 mmnodules,necroses,ulcersandcalci-

ficationofthebladderwall,pyelonephrosisandhydronephrosis,urethral

strictures,lesionsinthesexualorgans.Insomeendemicareas,anincreased

incidenceofurinarybladdercancerhasbeenassociatedwiththeS.hemato-

biuminfection.

SchistosomagranulomaintheLiver

Fig. 1 0. 5 A section of an

eggisvisibleinthecenter

ofthegranuloma.

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Kayser, Medical Microbiology © 2005 Thieme