Medical Microbiology

560 10 Helminths

Cestoda(Tapeworms)

General.Varioustapewormspeciescanparasitizeinthesmallintestineof

humans,includingspeciesfromthe“lower”(Pseudophyllida)and“higher”

(Cyclophyllida)cestodes(fromkestos=ribbon).Thesecestodespeciesare

hermaphroditesandconsistofthehead(scolexor“holdfast”),followedby

anunsegmentedgerminativesection(neck)andaposteriorchainofseg-

ments(proglottids).Therearenodigestiveorgans,sonutrientsaretaken

upthroughtheabsorptiveintegument.Thelifecycleofcestodesinclude

oneortwointermediatehosts.

Humanscanalsobeinfectedbylarvalstagesofvarioustapewormspecies

(cysticerci,metacestodes).Thesestagesdevelopinbodytissuesandgenerally

causeconsiderablygreaterpathologicaldamagethantheintestinalcestode

stages.

Taeniaspecies

Causativeagentsoftaeniosisandcysticercosis

&TaeniosisisasmallintestineinfectionofhumanscausedbyTaeniaspecies.

InthecaseofT.saginata,theintermediatehostsarecattle,inthemusculature

ofwhichmetacestodes(cysticerci)developandcanbeingestedbyhumans

whoeatrawbeef.Theinfectionrunsaninapparentcourseorisassociated

withmildintestinalsymptoms.ThemetacestodesofT.soliumdevelopin

themusculatureofpigs,orthroughaccidentalinfectioninhumansaswell

(CNS,eyes,musculature,skin),causingcysticercosis.T.saginataasiaticais

closelyrelatedtoT.saginata,butitsmetacestodesparasitizemainlyinthe

liversofpigsandruminants. &

Taeniasaginata(BeefTapeworm)

CausativeagentofT.saginatataeniosis

Occurrence.Thisspeciesoccursworldwide;thenumberofinfectedhumans

isestimatedtobebetween 40 and 60 million.Oneindicatorofinfectionfre-

quencyistheprevalenceofT.saginata-cysticercosisincattle(averagepreva-

lenceinEuropeapprox.0.3– 6 %,insomenon-Europeanregionsmorethan

50 %).

Parasites,lifecycle,andepidemiology(seeFig. 1 0. 8 ,p.563).T.saginata

(taenia:ribbon;saginatus:fattened)growsaslongas 10 mandhasascolex

withfoursuckersbutarostellumandhooksarelacking(seeT.solium).The

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Kayser, Medical Microbiology © 2005 Thieme