Medical Microbiology

Platyhelmintha(syn.Platyhelminthes) 561

proglottidsattheposteriorendofthechainarelongerthanwideandeach

containsatreelikebrancheduteruscontaining 80000 – 100000 eggs(=grav-

idsegments)(Fig. 1 0.7c,d).Theeggsarereleasedwhenaproglottiddetaches

fromthetapewormintheintestinallumenorwhenasegmentdisintegrates

outsidethehost.Theeggsaresmall(diameterapprox. 30 – 40 lm)andround

(Fig. 1 0. 1 ,p. 54 4).Theoutershellformsathick,brownish,radiallystripedem-

bryophoreenclosinganoncospherewiththreepairsofhooks.Theeggsare

highlyresistantandcanremaininfectiveinamoistenvironmentforweeksor

months(however,susceptibletodesiccation!).Carriedbyfecesofhumans

infectedwithTaenia,theycontaminatepasturesorfeedeitherdirectlyor

viasewage.Whencattle(orbuffalo)ingesttheeggs,theoncosphereshatch

inthesmallintestine,migrateintotheintestinalwall,andaretransported

withthebloodstreamintothestriatedmusculature,inwhichtheydevelop

intotheinfectivemetacestodesorcysticerci(=Cysticercusbovis)withinthree

tofourmonths.Eachcysticercusisapea-sized,fluid-filledcystcontaininga

singleinvaginatedscolex(Fig. 1 0.7e).

Humansareinfectedbyingestingraworundercookedbeefcontaining

cysticerci.Inthesmallintestine,thecysticercusevaginatesthescolex,at-

Cestodes

5 mm

a

c d

b

e

(^10)
m
m
10 mm
Fig. 1 0.7 a Chain of pro-
glottids(strobila)ofDiphyl-
lobothrium sp., unstained;
bstrobilaofDiphyllobothrium
latum,stained;cstrobilaof
Taenia saginata, unstained;
d gravid proglottid of T.
saginata,stained;emetaces-
todeofT.saginatainbovine
musculature(Fig.e:Institut
fu ̈rParasitologiederTiera ̈rztli-
chenHochschuleHannover).
10
Kayser, Medical Microbiology © 2005 Thieme