Medical Microbiology

Arachnida 611

Occurrence.ScabiescausedbySarcoptesscabieivar.hominisdoesnotoccur

frequentlyinEurope,althoughoccasionaloutbreaksareseeninschool

classes,families,seniorcitizens’homes,andothergroups.

Morphologyandbiology.Sarcoptesscabiei:mitesabout0.2–0.5mmlong

withovoidbodies.Theadultsandnymphshavefourpairsoflegs(Fig.

11 .1b),thelarvahasthreepairsoflegs.Followingtransmissiontoahuman

hostthefemalemitespenetrateintotheepidermisandbegintotunnel.The

resultingwindingburrowsareusually 4 – 5 mmandsometimesaslongas

10 mm.Ovipositionbeginsafteronlyafewhours.Six-leggedlarvaehatch

fromtheeggsafterafewdays.Infurthercourseofdevelopmentinvolving

moltings,thelarvaetransformintoprotonymphs(nymphI),thendeuto-

nymphs(nymphII),andfinallyadultmalesandfemales.Theentirelifecycle

takestwotothreeweeks.Thelifespanofthefemalemitesisfourtosixweeks.

Epidemiology.Transmissionisbyclosecontact(sexualpartners,family

members,schoolchildren,healthcarestaff)frompersontoperson,whereby

femalemitestranslocatetotheskinofanewhost.Indirecttransmissionon

clothes(underclothes),bedlinens,etc.isnotaprimaryroute,butshouldbe

consideredasafactorincontrolmeasures.Withoutahost,mitesusuallydie

offwithinafewdays.Miteinfectionscanalsobeacquiredfromanimalsto

whichhumanshavecloseskincontact.

Clinicalmanifestations.AnearlysignofaninitialinfestationwithSarcoptes

mitesistheprimaryefflorescencewithmitetunnelsupto 2 – 4 mmand

sometimes 10 mmlong—threadlike,irregularlywindingburrowsreminiscent

ofpencilmarkings.Thefemalemiteisfoundattheendoftheburrowina

smallswelling.

Followinganinapparentperiodofaboutfourtofiveweeks,duringwhich

timeahypersensitivityresponsetomiteantigensdevelops,thescabiesex-

anthemamanifestsintheformoflocalorgeneralizedpruritus,whichispar-

ticularlybothersomeintheeveningwhenbodyheatisretainedunderthe

bedcovers.Theevolvingskinlesionsarepapulousorpapulovesicularex-

anthemaandreactionsduetoscratching.Inadults,theselesionsareseen

mainlyintheinterdigitalspacesandonthesidesofthefingers,onthewrists

andanklesandinthegenitalregion.Childrenalsooccasionallyshowfacial

lesions.

Aspecialformoftheinfestationmaydevelopinimmunocompromised

patients:scabiescrustosa(formerlyscabiesnorvegica).Thistypeischarac-

terizedbypronouncedcrusted,flakinglesions,particularlyintheheadand

neckregion.Massivereproductionofthemitesmakesthisconditionhighly

contagious.

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Kayser, Medical Microbiology © 2005 Thieme