Medical Microbiology

Arachnida 609

Biology.ThevariousstagesofI.ricinusaredependentonbloodmealsfrom

vertebratesthroughouttheirdevelopmentalcycle.Havingselectedasuitable

locationonahost,afemaletickinsertsherpiercingmouthpartsintotheskin

withinabout 10 minutes.Usingclawlikeorgansatthetipofstylettelike

mouthparts,thechelicerae,thetickcutsawoundintowhichtheunpaired,

barbed,pinecone-shapedhypostomeistheninsertedtoanchortheparasite

intheskin.Whilesuckingblood,tickssecretelargeamountsofsaliva,con-

tainingcytolytic,anticoagulative,andothertypesofsubstances.Theyingest

blood,tissuefluidanddigestedtissuecomponents.Theweightofthefemale

increasesconsiderablyduringabloodmeal.Whencompletelyengorged,the

tickresemblesaricinusseed.Theepidemiologicallyimportantfactoristhe

possibleingestionofpathogenswiththebloodmeal,whichcan,atafollow-

ingbloodmealinthetick’snextdevelopmentalstage,beinoculatedintoan-

othervertebratehost(horizontaltransmission).Femaletickseventransmit

certainpathogensbythetransovarialroutetothenextgenerationofticks

(verticaltransmission).

Table 11. 2 summarizesthelifecycleofI.ricinus.Theoveralldevelopment

periodmaybeinterruptedbyperiodsofinactivityandstarvation(maximum

starvationcapacity 1 3–37months,dependingonthestage)andcantherefore

takefromonetothreeyears.

Epidemiology.I.ricinusoccurswidelyinEurope,bothinlowlandandmoun-

tainousregionsupto 800 – 1000 mabovesealevel,occasionallyevenhigher.

Thehabitatspreferredbythisspeciesincludeconiferous,deciduous,and

mixedforestswithplentifulunderbrushandadensegreenbelt.Thedifferent

Table 11. 2 LifeCycleofIxodesricinus

Developmentalstages: Egg! Larva! Nymph! Imago

Hostgroupscommonly

usedforbloodfeeding:

• Rodents,
  birds,
  (humans)^1

Birds,

mammals^2 ,

humans

Domesticand

wildruminants,

dogs,cats,

horses,andother

animalspecies^2 ,

humans

Durationofbloodsucking,

indays:

• 2–6 3– 7 5– 14

Tickhabitatwhennot

attachedtoahost:

Humidsoil,lowvegetation,areasofwoodlandwith

underbush,meadowswithhighgrass,gardensetc.

(^1) Occasionally. (^2) Manydifferenthostspecies;inEuropeabout35.
11
Kayser, Medical Microbiology © 2005 Thieme