Medical Microbiology

Insects 613

Parasitespecies.Twospeciesofliceinfesthumans,oneofwhichisdivided

intotwosubspecies(Table 11. 3 ).

Generalmorphologyandbiology.Licearedorsoventrallyflattenedinsects,

about 1 .5– 4 mminlength,wingless,withreducedeyes,short(five-segment-

ed)antennae,piercingandsuckingmouthparts,andstrongclawsdesignedto

clingtohairs(Fig. 11 .1c).

Licedevelopfromeggs(callednits)gluedtohairs.Thehatchedlouse

growsandmoltsthroughthreelarvalstagestobecomeanadult.Liceremain

onahostpermanently;bothmalesandfemalesarehematophagousandre-

quirefrequentbloodmeals.Licearehighlyhost-specific,sothatanimalscan-

notbeasourceofinfestationforhumans.

Medicalsignificance.Amongthevariousspeciesofliceonlythebodylouseis

avectorofhumandiseases.Ittransmitstyphusfever(causedbyRickettsia

prowazekii),relapsingfever(causedbyBorreliarecurrentis),andtrenchfever

(causedbyBartonellaquintana).IncentralEurope,themedicalimportanceof

liceisnotduetotheirvectorfunction,butrathertothedirectdamagecaused

bytheirbites(seebelow).

Pediculushumanuscapitis(HeadLouse)

Morphologyandbiology.Ovalbody,length2.2–4.0mm,morphologyvery

similartothebodylouse.Nitsare0.5–0.8mmlong.Localizationismainly

inthehaironthehead,occasionallyalsoonotherhairyareasofthe

headorupperbody.Thenitsaregluedtothebaseofthehairnearthe

skin.Durationofdevelopmentfromnittoadultis 17 days.Thelifespanof

adultsonhumanhostaboutonemonth,survivaloffhostatroomtempera-

tureisforuptooneweek.

Occurrenceandepidemiology.Occursworldwide;incentralEuropeitisnot

frequent,butepidemic-likeoutbreaksofheadlouseinfestationareobserved

regularly,especiallyinschoolsandkindergartens,homes,groupsofneglected

Table 11. 3 LicethatInfestHumans

Species Mainlocalizationofliceandsitesofoviposition

Pediculushumanuscapitis

(headlouse)

Haironthehead,rarelyonbeardhairsorhairysiteson

upperbody

Pediculushumanuscorporis

(bodylouse)

Stitching,seams,andfoldsinclothes,especiallywhere

itisindirectcontactwiththebody

Phthiruspubis(crablouse) Hairofpubicarea,morerarelyintheabdominaland

axillaryregions,beard,eyebrows,andeyelashes

11

Kayser, Medical Microbiology © 2005 Thieme