Medical Microbiology

582 10 Helminths

soil,etc.Whilepenetratingtheskinthelarvaeshedtheirsheathsandmigrate

intolymphaticandbloodvessels.Onceinthebloodstream,theymigratevia

therightventricleoftheheartandbytrachealmigration(conf.Ascaris)into

thesmallintestine,wheretheydeveloptosexualmaturity.Theprepatent

periodlastsfivetosevenweeksorlonger(reason:arrestedlarvaldevelop-

ment).Followingoralinfection,immediatedevelopmentintheintestineis

probablypossible(i.e.,withouttheotherwisenecessarymigrationthrough

variousorgans).Theparasitescansurviveinthehumangutforoneto 15

years.

Clinicalmanifestations.Hookwormsarebloodsuckers.Thebuccalcapsule

damagesthemucosaandinducesinflammatoryreactions.Theintestinaltis-

suedamageresultsindiarrheawithbloodyadmixtures,steatorrhea,lossof

appetite,nausea,flatulence,andabdominalpains.Generalsymptomsinclude

irondeficiencyanemiaduetoconstantbloodloss,edemascausedbyalbumin

lossesandweightlossduetoreducedfooduptakeandmalabsorption.Blood

eosinophiliaisoftenpresent.Mildinfectionscauselittleofclinicalnote.

Diagnosis.Diagnosisreliesonfindingofeggsinstoolsamples.Theeggsare

thin-shelledandoval;whenfreshtheycontainonlytwotoeightblastomeres

(Figs. 1 0. 1 and 1 0. 14 ).Theeggsinolderstoolsampleshavealreadydeveloped

alargernumberofblastomeresandcannotlongerbedifferentiatedfromthe

eggsoftheraretrichostrongylidspecies(Trichostrongylusetc.).Insuchacase,

afecalculturemustbepreparedinwhichthird-stagelarvaedevelopshowing

featuresforadifferentialdiagnosis.Someinfectedpersonsproducedetect-

ableserumantibodies.

Therapyandcontrol.Drugseffectiveagainsthookwormsarepyrantel,me-

bendazole,andalbendazole.Practicablepreventiveandcontrolmeasures

includemasschemotherapyofthepopulationinendemicregions,reduction

ofdisseminationofhookwormeggsbyadequatedisposaloffecalmatterand

sewage,andreductionofpercutaneousinfectionbyuseofproperlyprotec-

tivefootwear(seealsofilariosis,p.593).

Strongyloides

StrongyloidesstercoralisandS.fuelleborni

(DwarfThreadworms)

Causativeagentsofstrongyloidosis

Parasitesandoccurrence.Strongyloidesstercoralis,whichparasitizeshu-

mans,dogs,andmonkeys,occursmainlyinmoist,warmclimaticzones,

andmorerarelyintemperatezones(e.g.,southernandeasternEurope).

About 50 – 100 millionpersonsareinfectedworldwide(WHO, 1 995).Stron-

10

Kayser, Medical Microbiology © 2005 Thieme