Medical Microbiology

Toxoplasmagondii

Causativeagentoftoxoplasmosis

&Toxoplasmagondiiis thecausativeagentofazoonosisthatoccurs

worldwidewithhighprevalences(upto 80 %dependingonregionand

age).Humansareinfectedbyingestingoocystsexcretedbythedefinitive

hosts(cats)orbyeatingunprocessedmeatcontainingToxoplasmacysts.

Ifawomencontractstoxoplasmosisforthefirsttimeduringpregnancy,

diaplacentaltransmissionofthepathogentothefetusispossiblewithpoten-

tialsevereconsequences(forexamplemalformations,eyedamage,clinical

symptomsduringchildhood).Thereis,however,norisktothefetusfrom

motherswhohadbeeninfectedbeforetheirfirstpregnancyandhavepro-

ducedserumantibodies(about 35 – 45 %).Latentinfectionscanbeactivatedby

immunodeficiencies(e.g.,inAIDSpatients)andmayresultincerebralorgen-

eralizedsymptomatictoxoplasmosis.Serologicalsurveillanceinpregnant

womenisimportanttopreventprenatalinfections. &

Occurrence.T.gondiioccursworldwide.Thelowlevelofhostspecificityof

thisorganismexplainsitsreadyabilitytoinfectawidespectrumofwarm-

bloodedvertebratespecies(forexamplehumans,sheep,pigs,cattle,horses,

dogs,cats,wildmammals,birdspecies).Itisestimatedthatapproximately

one-thirdoftheworldpopulationisinfectedwithT.gondii,althoughpreva-

lencesvarywidelydependingonageandregion.Accordingtoaseroepide-

miologicalstudyinSwitzerland(publishedin 1 995)of 4000 personsaged

oneto 7 0,anaverageof 52 %wasinfectedwithseroprevalenceratesindif-

ferentagegroupsasfollows:onetonineyears: 24 %, 20 – 39 years: 43 %,and

40 – 70 years: 69 %.Of 9000 pregnantwomen, 46 %wereinfected.Womenof

childbearingagegroupsinotherEuropeancountriesshowedeitherloweror

higherseroprevalences.Highprevalenceswerealsoobservedinvariousan-

imalspecies(seeEpidemiologyp. 51 4).

Parasite.VariousstrainsofT.gondiidifferinvirulenceandcertainbiological

andgeneticcharacteristics.ThelifecycleofT.gondiiincludesvariousstages:

&Tachyzoites(endozoites)(Fig.9. 1 2a,b)areproliferativeformsthatre-

producerapidlywithinaparasitophorousvacuoleinnucleatehostcellsby

meansofendodyogeny(endodyogeny:formationoftwodaughtercells

fromamothercellbyendogenousbudding).Thetachyzoitesaresickleshaped

(toxon:bow)cellsabout 4 – 7 lmlongand 2 – 4 mmwide.Anapicalcomplexis

locatedattheanteriorpole,consistingofservealcomponents,including

theconoid(aconicalstructureofspirallyarrangedmicrotubuli),apole

ringcomplex,therhoptries,andmicronemes(Fig.9. 12 b).Theapicalcomplex

508 9 Protozoa

9

Kayser, Medical Microbiology © 2005 Thieme