Medical Microbiology

werefoundinbothhumansanddomesticanimals(e.g.,cattle,sheep,dogs).

TheseandotherfactssupporttheconclusionthatsomestrainsofG.duo-

denaliscanbetransmittedfromvertebrateanimalstohumansandthat

giardiosisisazoonosis.Humansareapparentlythemostimportantreservoir

hostsandcertainmammaliananimalspeciesareconsideredadditional

sourcesofinfection.

Thecystsexcretedinstoolareresponsibleforspreadingtheinfection.

Theyremainviableforuptothreeweeksinmoistsurroundingsat 218 C

anduptoaboutthreemonthsincoolwater(8 8 C).Thetrophozoites,bycon-

trast,dieoffsoonoutsidethehost.Infectionisperos,wherebycystsaretrans-

mittedbythefecal-oralroutefrompersontoperson(withinfamilies,kinder-

gartens,betweenhomosexuals,etc.)orinfoodanddrinkingwater.Numerous

epidemicoutbreaksofgiardiososduetocontaminateddrinkingwaterhave

beendescribedintheUSandothercountrieswithupto 7000 personslocally

involved.

Pathogenesisandclinicalmanifestations.Inthesmallintestine,G.intesti-

naliscancauseinflammationaswellasothermorphologicalchangesand

malabsorption.Gallbladderinfectionshavealsobeendescribed.Thepatho-

genesisisunclear;newdataprovideevidencethatGiardiaproducetoxinlike

proteins.

Thecourseofinfectionisfrequentlyasymptomatic.Theparasitecanbe

eliminatedspontaneouslywithinafewweeks;ontheotherhand,itmayper-

sistforyears.Theabilitytoproducevariablesurfaceproteinsmayinfluence

eliminationandpersistence.Patientswithsymptomaticinfectionsexperi-

encechronicandrecurrentdiarrhea,steatorrhea,andsignsofmalabsorption

aswellasupperabdominalpains,vomiting,occasionallyfever,andweight

loss.

Diagnosis,therapy,andprevention.Thestandarddiagnosticmethodisstool

examinationusingtheSAFCtechniquetodetectcystsand(morerarely)tro-

phozoites(p. 62 1).Trophozoitescanalsobefoundinduodenalaspirate.IFAT

andELISAkitsarenowalsoavailabletodetectGiardia-specificstructuraland

solubleantigensinstoolsamples.Nitroimidazolecompoundsareusedfor

chemotherapyofinfections,forinstancemetronidazole,ornidazole,andti-

nidazole(seeTable9. 5 ),aswellasthebenzimidazolecompoundalbendazole

andtherecentlyintroducednitazoxanide(nitrothiazolecompound).Prophy-

lacticmeasuresarethesameasforamebosis(p. 4 99).Avaccineinducesa

reliablyprotectiveeffectindogsandcats.

480 9 Protozoa

9

Kayser, Medical Microbiology © 2005 Thieme