Platyhelmintha(syn.Platyhelminthes) 573&Definitivehosts,intermediatehosts,andaccidentalhosts.Themost
importantdefinitivehostsforE.multilocularisareredandpolarfoxes,
althoughotherwildcarnivores(e.g.,coyotes,raccoons,wolves)aswellas
dogsandcatscanalsocarrythistapewormspecies.Theintermediatehosts
areusuallyrodents(fieldmice,voles,muskrats,etc.).Accidentalhostsinclude
humansandvariousmammaliananimalssuchasmonkeyspecies,domestic
andwildpigs,horses,andevendogs.
&Lifecycle.TheE.multiloculariscycleissimilartothatofE.granulosus
(Fig. 1 0. 9 ).Innaturalintermediatehosts,protoscolecesdevelopinthemeta-
cestode(seedescriptionbelow)within 40 – 60 days.Ingestionofmetaces-
todescontainingprotoscolecesbyadefinitivehostresultsindevelopment
ofanewgenerationoftapewormsinitssmallintestinewithinfective
eggsproducedasearlyas 26 – 28 daysp.i.
&ThemetacestodeofE.multilocularisisaconglomeratewithanalveolar
structurecomprisedofsmallcysts(microscopicalto 3 cmindiameter)
surroundedbygranulomatousorconnectivetissue.Eachcystisstructured
asinE.granulosus,butcontainsagelatinousmass.E.multilocularisrarely
produce(smallnumbersof)protoscolecesinhumans(max. 10 %ofcases)
(Fig. 1 0. 1 0e,g,i).
Apathologicallysignificantaspectisthattheindividualcystsproliferateby
exogenousbuddingandthatthincellular,rootlikeextensionsofthegermi-
nativelayercaninfiltrateintosurroundingtissues.Presumably,cellgroups
releasedbythesestructuresorverysmallvesiclesspreadhematogenously
tocausedistantmetastases,e.g.,inthebrainorbones.Thereforethemeta-
cestodebehaveslikeamalignanttumor.Metacestodeconglomeratescan
growto 20 cmindiameterinhumansandmaydevelopcentralnecrosis
andcavitation.
Epidemiology.InEurope,E.multilocularisdevelopsmainlyinasylvaticcycle
withtheredfoxasthedefinitivehostandmainsourceofhumaninfections.
DogsandcatscanbecomecarriersofE.multilocularisbyeatingsmallmam-
malscontainingmetacestodes.Intheenvironment,theeggsofE.multi-
locularisshowresistancesimilartothatofE.granulosus.Theeggsaretrans-
mittedtohumansbyvariousroutes,butitisnotyetclearwhicharethemost
important:
&ContaminationofhandswitheggsofE.multilocularisbytouchingdefini-
tivehosts(fox,dog,cat)havingsucheggsadheringtotheirfurorfromwork-
ingwithsoilorplantscontaminatedbythefecesofdefinitivehosts.
&Ingestionofcontaminatedfood(wildberries,vegetables,windfallfruit,
etc.)ordrinkingwater.10Kayser, Medical Microbiology © 2005 Thieme