Medical Microbiology

568 10 Helminths

moreprotoscoleceswithfoursuckersandtowrowsofrostellarhooks

(Fig. 1 0. 10 h).Thethinbroodcapsulesbursttoreleasefreeprotoscoleces

intothehydatidfluid,whichform,togetherwiththebroodcapsules,their

remainsandcalcareouscorpusclestheso-called“hydatidsand.”Thesize

ofthecystsdependsontheirageandotherfactors.Theaveragecystdiameter

inhumansis 1 – 15 cm,althoughitcanvarybetweenafewmmand 20 cm.

Cystsinhumansoftencontainsmallerdaughtercysts.

ThelifecycleiscompletedwhencarnivoresingestE.granulosuscystscontain-

ingmatureprotoscoleceswithslaughteroffal(viscera)orprey.Sexuallyma-

turestagesthendevelopinthesmallintestineofthedefinitivehostswithin

fivetoeightweeks.

Epidemiology.ThereareanumberofstrainsofE.granulosusthatdifferin

morphological,biological,andgeneticfeaturesandpartiallyalsointheirin-

fectivitytohumans.Worldwide,formostofthehumancasesthesheepstrain

isresponsiblewhichdevelopsinacycleinvolvingdogsandsheep(andother,

lessimportant,intermediatehosts).

HumansareinfectedbyperoralingestionofEchinococcuseggs,eitherdur-

ingdirectcontactwithtapewormcarriersorindirectlybyuptakeofconta-

minatedfoodordrinkingwater.Echinococcuseggsremainviableformonths

inamoistenvironmentandcanalsosurvivethewinter.Theyarekilled

rapidlybydesiccation.Theycanalsobekilledbyheat(75– 1008 C)within

afewminutesandbydeep-freezingat–7 0 or–80 8 Cforfourortwodays,

respectively.Standardchemicaldisinfectantshavenoeffect.

ThemeanannualincidenceofCEvariesinthecountriesandareasofthe

Mediterraneanregionbetweenaboutoneto 10 newclinicalcasesper 100000

inhabitants,althoughhigherincidences(> 40 cases/1 00000 inhabitants)

havebeenobservedinotherendemicareas(e.g.,SouthAmericaandChina).

Pathogenesisandclinicalmanifestations.Severalclinicalparametersof

humanCEandAEarepresentedandcomparedinTable 1 0. 3.

TheCEisalwaysasymptomaticinitiallyanditremainssoforlongerpe-

riodsinaproportionofcases(upto 30 %),especiallywhenonlysmall,well-

Fig. 1 0. 10 aEchinococcusgranulosus,adult;bE.multilocularis,adult;cdogintes-

tinewithE.granulosus;dcysticechinococcosisinhumanliver:mothercystof

E.granulosuswithdaughtercysts;ealveolarechinococcosisinliver;fcystof

E.granulosus:histologicalsectionthroughcystwall;gsectionthroughE.multi-

locularisinhumanliver;hisolatedprotoscolecesofE.granulosus;isectionthrough

metacestodesofE.multiloculariswithprotoscoleces,fromrodent.(d:A.Akov-

biantz,Waidspital,Zurich.) "

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Kayser, Medical Microbiology © 2005 Thieme