Medical Microbiology

Arachnida 607

asvectorsofviruses,bacteria,protozoa,orhelminths.Somespeciesorstages

ofarthropodsarecapableofpenetratingtodeeperskinlayersorintobody

openingsorwounds,wheretheireffectissimilartothatofendoparasites.

Onlyasmallselectionofmedicallyimportantarthropodswillbedescribed

inthefollowingchapter(seeTable 11. 1 ),inparticularthosethatareof

significanceincentralEurope.Thereaderisreferredtotheliteraturefor

moredetailedinformation(seep. 660 ).

Arachnida

Ticks(Ixodida)

General.TheorderIxodidaincludestwoimportantfamilies,theArgasidae

(softticks)andIxodidae(hardticks).Thelatteristhemostsignificantgroup

worldwide.WewillonlybeconsideringtheIxodidaehere.

Approximately 20 hardtickspeciesareindigenoustowesternandcentral

Europe,belongingtothegeneraIxodes,Rhipicephalus,Dermacentor,and

Haemaphysalis.ThemostimportantspeciesisIxodesricinusthataccounts

forabout 90 %ofthetickfaunainthisregion.Forthisreason,humantickbites

incentralEuropeareinmostcasescausedbyI.ricinusandonlyoccasionally

byothertickspecies.

Ixodesricinus

VectorofthecausativeagentsofLymeborreliosisandtickborneencephalitis

&Ixodesricinus,(commonsheeptick,castorbeantick)isthemostfrequent

hardtickspeciesincentralEurope.Themedicalsignificanceofthisspeciesis

duetoitsroleasvectorofthecausativeagentsofLymeborreliosis,tickborne

encephalitis(Europeantickborneencephalitis,“earlysummermeningoence-

phalitis,”ESME),andotherpathogens.Ticksthathaveattachedtotheskin

shouldbemechanicallyremovedassoonaspossibletoreducetheriskof

infection. &

Morphology.Male:about 2 – 3 mmlongwithahighlychitinizedscutum

coveringtheentiredorsalsurface.Female: 3 – 4 mm,upto 12 mmwhenfully

engorgedafterabloodmeal;thescutumcoversonlytheanteriorportionof

thebody(Fig. 11 .1a).Adultsandnymphs(thelatterabout 1 mmlong)have

fourpairsoflegs,thesmallerlarvae(about0.5mmlong)onlythreepairs.

Tickspossesscharacteristicpiercingmouthparts.

11

Kayser, Medical Microbiology © 2005 Thieme