Medical Microbiology

Nematoda(Roundworms) 585

Serumantibodiesarepresentinabout 85 %ofimmunocompetentpersons

withS.stercoralislarvaeintheirstools(Table 11. 5 ,p.626).Ininfections

withotherhelminths,especiallyfilariae,cross-reactionsoccurthatcanbe

avoidedbyusingrecombinantproteinsasantigensintheELISA.

Therapyandprevention.Themaindrugsusedfortherapyarealbendazole,

mebendazole,andmorerecentlyivermectin.Preventivemeasuresresemble

thosetakentopreventhookworminfections.Travelersreturningfromtropi-

calcountriesshouldbethoroughlyexaminedforStrongyloidesinfectionsbe-

foreanyimmunosuppressivemeasuresareinitiated(e.g.,forakidneytrans-

plantation).

Enterobius

Enterobiusvermicularis(Pinworm)

Causativeagentofenterobiosis(oxyuriosis)

Occurrence.Thepinwormoccursinallpartsoftheworldandisalsoafre-

quentparasiteintemperateclimatezonesanddevelopedcountries.Theage

groupsmostfrequentlyinfectedarefive-tonine-year-oldchildrenandadults

between 30 and 50 yearsofage.

Parasite,lifecycle,andepidemiology.Enterobiusvermiculariswhichbe-

longstotheOxyuridahasaconspicuouswhitecolor.Themalesare 2 –

5 mmlong,thefemales 8 – 13 mm.Thelong,pointedtailofthefemalegives

thepinwormitsname.

Sexuallymaturepinwormsliveonthemucosaofthelargeintestineand

lowersmallintestine.Followingcopulation,themalessoondieoff.Thefe-

malesmigratetotheanus,usuallypassingthroughthesphincteratnight,

thenmoveaboutontheperianalskin,wherebyeachfemalelaysabout

10000 eggscoveredwithastickyproteinaceouslayerenablingthemtoad-

heretotheskin.Insevereinfections,numerouslivingpinwormsareoften

shedinstoolandareeasilyrecognizableasmotilewormsonthesurface

ofthefeces.

Theeggs(about 50! 30 lminsize)areslightlyasymmetrical,ellipsoidal

withthinshells(Fig. 1 0. 1 ,p. 54 4).Withtheirstickysurfacetheyadheretoskin

andotherobjects.Freshlylaideggscontainanembryothatdevelopsintoan

infectivefirst-stagelarvaatskintemperatureinabouttwodays.Eggsthat

becomedetachedfromtheskinremainviablefortwotothreeweeksina

moistenvironment.

Infectionoccursmainlybyperoraluptakeofeggs(eachcontaininganin-

fectivelarva)thataretransmittedtothemouthwiththefingersfromtheanal

regionorfromvariousobjects.Thestickyeggsadheretotoysanditemsof

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Kayser, Medical Microbiology © 2005 Thieme