Medical Microbiology

580 10 Helminths

Followingperoralingestionofinfectiveeggs,thelarvaehatchinthedi-

gestivetract,migrateintothemucosa,andreturntotheintestinallumenafter

ahistotropicphaselastingabout 10 days.Theretheadultstagesdevelopand

remainwiththeirslenderanteriorendsanchoredinthemucosa.Theprepa-

tentperiodistwoandahalftothreemonths,theparasitecanliveforseveral

years.

Amoist,warmclimateandunhygienicpracticesfavorinfections,which

arecontractedasdescribedforAscaris.

Pathogenesisandclinicalmanifestations.Thewhipworms,withtheirthin

anteriorendsanchoredinthemucosa,ingestblood.Mildinfectionsare

asymptomatic.Moresevereinfections,withhundredsorseveralthousand

whipworms,causecatarrhalorhemorrhagicinflammationsofthelargein-

testine.

Diagnosis,therapy,andcontrol.ATrichurisinfectionisdiagnosedbydetect-

ingeggsinstool(Fig. 1 0. 1 ,p. 54 4).Effectivedrugsincludealbendazole,me-

bendazole,andoxantel.Seeascariosisforappropriatepreventionandcontrol

measures.

AncylostomaandNecator(Hookworms)

Causativeagentsofancylostomosisandnecatorosis(hookworminfection)

Parasites.AncylostomaduodenaleandNecatoramericanusarecommonpara-

sitesofthehumansmallintestine,causingenteritisandanemia.Infectionis

mainlybythepercutaneousroute.ThedogparasiteAncylostomacaninumhas

beenidentifiedasthecauseofeosinophilicenteritisinhumans.Larvaeof

varioushookwormspeciesfromdogsandothercarnivorescanpenetrate

intohumanskin,causingtheclinicalpictureof“cutaneouslarvamigrans”

(p.602).

Occurrence.Humanhookworminfectionsaremostfrequentinthesubtro-

picsandtropics(forinstanceinsouthernEurope,Africa,Asia,southernUS,

CentralandSouthAmerica).Thenumberofpersonsinfectedworldwideis

estimatedatabout 1 .25billion(WHO, 199 8).IncentralEurope,hookworm

infectionsareseenmainlyintravelersreturningfromthetropicsoringuest

workersfromsoutherncountries.

Morphology,lifecycle,andepidemiology(Fig. 1 0. 14 ).Thehookwormsthat

parasitizehumansare0.7– 1 .8cmlongwiththeanteriorendbentdorsallyin

ahooklikeshape(ankylos:bent,stoma:mouth,necator:killer).Theentrance

tothelargebuccalcapsuleisarmedwithtoothlikestructures(Ancylostoma)

orcuttingplates(Necator).Thethin-shelled,ovaleggs(about 60 lmlong)

containingonlyasmallnumberofblastomeresareshedwithfeces.Inone

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Kayser, Medical Microbiology © 2005 Thieme