Medical Microbiology

576 10 Helminths

intestineofhumansandfish-eatingmammalssuchaspigs,dogs,andcats.

Theparasitehastwoelongatedgrooves(bothria)onitshead,itis 2 – 15 m

longwithnumerous(upto 400 0)proglottids(Fig. 1 0.7a,b,p. 56 1).The

oval,yellow-brown,operculatedeggs(approx. 70! 50 lm)aresimilarto

thoseoftrematodes(Fig. 1 0. 1 ,p. 54 4).Thelifecycleincludescopepodsaspri-

maryandfreshwaterfishassecondaryintermediatehosts.Humansacquire

theinfectionwheneatingraworundercookedfishcontaininginfectivestages

(plerocercoids)ofthetapeworm.Developmentofasexuallymaturetape-

wormcanbecompletedwithin 18 days.

ClinicalmanifestationsThecourseofaDiphyllobothriuminfectionisoften

devoidofclinicalsymptoms,withonlymildgastrointestinaldistressin

somecases.AnemiaandothersymptomsduetovitaminB1 2 uptakeby

theparasiteisobservedinabout 2 %oftapewormcarriers.

Diagnosis,therapy,andprevention.Diagnosisismadebydetectionofeggs

instool,sometimesproglottidsareexcreted.Praziquantelisasuitabledrug

fortherapy.Preventivemeasuresincludewastewaterhygieneandnoteating

undercookedfish.Theplerocercoidscanbekilledbyboilingordeep-freezing

(2 4 hoursat–1 88 Cor 72 hoursat–1 08 C).

Nematoda(Roundworms)

General.Thenematodes(nema:thread)arethreadlike,nonsegmentedpara-

sites,afewmmto 1 minlength,withseparatedsexes.Theypossessacom-

plextegumentandadigestivetract.Themalesareusuallysmallerthanthe

femalesandareequippedwithcopulatoryorgansthatoftenshowfeatures

specifictoeachspecies.Developmentfromtheeggincludesfourlarvalstages

andfourmoltingsbeforetheadultstageisreached.Somespeciesrequirean

intermediatehosttocompletedevelopment.

IntestinalNematodes

&Ascarislumbricoides(largeroundworm),hookworms(Ancylostomaspe-

ciesandNecatoramericanus),andStrongyloidesstercoralis(dwarfthread-

worm)parasitizeinthesmallintestineofhumans;Trichuristrichiura(whip-

worm)andEnterobiusvermicularis(pinworm)liveinthelargeintestine.The

transmissionroutesandlifecyclesoftheseparasitesdiffer.S.stercoralisin-

fectionsacquiredinwarmcountriesmaypersistinalatentstateformany

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Kayser, Medical Microbiology © 2005 Thieme