Medical Microbiology

Platyhelmintha(syn.Platyhelminthes) 575

EchinococcusvogeliandE.oligarthrus

Causativeagentsofpolycysticechinococcosis

Thesetwospecies,endemicinCentralandSouthAmerica,developinwildanimal

cycles(bushdog/pacaandwildfelids/agoutis,pacaetc.,respectively).Inhumans,

theseorganismscausetherarepolycysticechinococcosis,whichaffectstheliver,

lungs,andotherorgans.

Hymenolepis

Hymenolepisnana(DwarfTapeworm)

Causativeagentofhymenolepiosis

Occurrence,morphology,andlifecycle.Hymenolepisnana, 1 – 4 cmlong

(rarely 9 cm)and 1 mmwide,isasmallintestinalparasitethatoccursworld-

wide,thehighestprevalencesbeingfoundinwarmcountriesandinchildren.

Thefinalhostsarerodentsandhumans.Infectionresultsfromperoralinges-

tionofeggs,fromwhichoncosphereshatchinthesmallintestine,penetrate

intothevilli,anddevelopthereintolarvae(cysticercoids).Thelarvaethen

returntotheintestinallumen,wheretheydevelopintoadulttapeworms

withintwotothreeweeks.Alternatively,H.nanadevelopsinacyclewith

anintermediatehost(insects:fleas,grainbeetles,etc.).Thecloselyrelated

speciesHymenolepisdiminuta(1 0 – 60 mm)isnotasfrequentinhumans.

Thedevelopmentalcycleofthisspeciesalwaysinvolvesintermediatehosts

(fleas,beetles,cockroaches,etc.).

Clinicalmanifestationsanddiagnosis.Infectionsareoftenlatent,butsome-

timescauseindeterminategastrointestinaldistress.Theeggs(elliptical,about

60! 50 lm,Fig. 1 0. 1 ,p. 54 4)arereleasedfromthecestodeintheintestine

andarefoundbynormalstoolexaminationprocedures.

Therapyandprevention.Praziquanteloralbendazolearethedrugsofchoice.

Preventivemeasuresincludegeneralhygieneandtreatmentofinfectedper-

sons.

Diphyllobothrium

Diphyllobothriumlatum(BroadTapeworm,FishTapeworm)

Causativeagentofdiphyllobothriosis

Occurrence,morphology,andlifecycle.Thistapewormisendemicinlake

regionsinEurope(aboveallinRussia,lessfrequentlyinScandinavia,Ger-

many,Switzerland,Italy,etc.),Asia,andAmericaandparasitizesinthesmall

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Kayser, Medical Microbiology © 2005 Thieme