Medical Microbiology

ofothergroups),andmitosomes(Entamoeba)(seeunderspecificprotozoan

groups).Motilestagesoftheparasiticprotozoamostlymovebymeansof

flagella,cilia,orpseudopodia.Somespeciesproduceresistantstages(cysts,

oocysts)inwhichtheparasitescansurviveoutsideoftheirhostsforlonger

periods.

Accordingtocurrenttheories,theprotozoaareaheterogeneousgroup

consistingofdifferentphylawithintheregnumofEukaryota.Thetermpro-

tozoahasnophylogeneticsignificancebutisstillusedasacollectivenamefor

thevariouseukaryoticunicellularorganisms.Theclassificationoftheproto-

zoaishighlycontroversial.Therefore,allclassificationsystemshavetobere-

gardedasprovisional(Table9. 1 ).

Giardiaintestinalis

Causativeagentofgiardiosis,lambliosis

&Giardiaintestinalis(syn.Giardialamblia,G.duodenalis),aparasiteof

worldwidedistribution,occursalsoinEuropewithrelativelyhighfrequency.

Itisaparasiteofthesmallintestineofhumansthatcancauseenteritis.In-

fectionoccursbyperoralingestionofGiardiacysts.Variousspeciesofmam-

maliananimalsarereservoirhosts. &

Occurrence.G.intestinalishasaworldwidedistributionwithprevalencerates

of 2 – 5 %inindustrializedcountriesandveryhighrates,upto 50 %,indevel-

opingcountries.Childrenuptotheageoffivearefrequentlyinfected.

Parasiteandlifecycle.Giardiaexistsintwomorphologicalforms:amotile

vegetativestage,thetrophozoite,andacyststage.Thetrophozoitesliveon

thesmallintestinemucosa(lessfrequentlyonthegallbladdermucosaaswell).

Theyresembleapearsplitlengthwise,are9–21lmlongand 5 – 12 lmwide

andpossesseightflagella,twonuclei—oneoneachsideofthelongitudinal

axis—andtwoclaw-shapedmedianbodies(Figs.9. 1 and9. 11 a).Theirdorsal

sideisconvex,theanteriorpartoftheventralsideformsaconcaveadhesive

disk.Reproductionisbymeansoflongitudinalbinaryfissionofthetropho-

zoites,whichareabletoproducevariantspecificsurfaceproteins.G.intes-

tinalisproducesovalcysts(8– 18 !7–1 0 lm)withfournuclei,flagella,and

claw-shapedmedianbodies.Thecysts(and,lessfrequently,trophozoites)

areexcretedinstool.Fig.9. 1 illustratesthelifecycleofG.intestinalis.

Epidemiology.ThegenusGiardiaincludesseveralspecies(G.intestinalis,

G.muris,G.agilis,etc.)thatshowmorphological,biological,andgeneticdif-

ferences.Giardiaisolatesobtainedfromhumansandvariousspeciesof

478 9 Protozoa

9

Kayser, Medical Microbiology © 2005 Thieme