Medical Microbiology

Platyhelmintha(syn.Platyhelminthes) 557

Dicrocoelium

Dicrocoeliumdendriticum(LancetLiverFluke)

Causativeagentofdicrocoeliosis

Thelancetliverfluke(0.5– 1 .0!0.2cm)(Fig. 1 0.6b),abileductparasiteinsheep,

cattle,andotherherbivores,occursfrequentlyinregionalfociinthenorthernhemi-

sphere(forinstancesouthernGermany,Austria,Switzerland,NorthAmerica).Itslife

cycleincludestwointermediatehosts(terrestrialsnailsandants).Humansbecome

infectedaccidentallywhentheyingestantscontaininginfectivemetacercariaeof

thelancetliverfluke.Suchinfectionsarerareandeitherrunanasymptomatic

courseormanifestinmildabdominalandhepaticsymptoms.Diagnosisisbased

ondetectionofeggsinstool(about 40! 25 lm,oval,darkbrown,containing

amiracidiumwithtworoundedgerminalcells)(Fig. 1 0. 1 .p.543).Ingestionofcon-

taminatedbeeformuttonlivercanresultineggexcretioninstoolwithoutinfection

(intestinalpassage).TheeggsofOpisthorchisandClonorchismustbetakenintocon-

siderationforadifferentialdiagnosis(Fig. 1 0. 1 ).Praziquantelhasbeenshowntobe

effectiveagainstDicrocoeliuminanimals(seealsoopisthorchiosis).

OpisthorchisandClonorchis

(CatLiverFlukeandChineseLiverFluke)

Causativeagentsofopisthorchiosisandclonorchiosis

&LiverflukesofthegeneraOpisthorchisandClonorchisoccurmainlyinriver

andlakeregionsofAsiaandEasternEurope;Opisthorchisisalsofoundfurther

westwardasfarasnorthernGermany.Thelifecycleoftheseorganismsin-

cludestwointermediatehosts(aquaticsnail,fish).Infectionsarecontracted

viarawfishcontaininginfectivestages(metacercariae).Diagnosisisbased

mainlyondetectionofeggsinstoolorduodenalaspirate. &

Parasitesandoccurrence.Themembersofthesegeneraresemblethelancet

liverfluke(Dicrocoeliumdendriticum)insize(length 1 – 2 cm)andform.The

positionandstructureofthetesticles(ophisten:posterior;orchis:testicle;

clon:branch)allowthediscriminationofgenera(Fig. 1 0.6c).

OpisthorchisandClonorchisoccurendemicallyinriverandlakeregions:

OpisthorchisfelineusinEurasia(Russia,Kazakhstan,Ukraine;otherendemic

foci intheBaltic countries, northernPoland, andnorthernGermany),

OpisthorchisviverriniinThailandandLaos,Clonorchissinensisinfar-eastern

RussiaandotherAsianareas(includingChina,Taiwan,VietnamandKorea).

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Kayser, Medical Microbiology © 2005 Thieme