Toxoplasmagondiiisasmallintracellularparasite,whoselivecyclehasasexualandanasexualphase.Sexualdevelopmentisrestrictedtotheintestinalcellsof(probablyexclusively)cats;theoocystsformedareexcretedandduetotheirresistantcellwallstheymaybeinfectiousunderadvantageouscircumstancesforatleast1year.AnimalsandmanareintermediatehostsfortheasexualproliferationofT.gondii:theingestedparasiteswillproliferateexplosivelywithinthehostcellslysingthemeventually.Theydisseminatethroughoutthebodyviacirculationandlymphaticsystemandthoughmayinfectanycelltype.Inmuscleandbraincellscystsareformedwhicharespheroidalandabout5-100µmindiameter.Cystsarevirtuallyimmortalintheintermediatehost.Toxoplasmagondiiisthemostcommonparasiteinhumans,butitsabundance(7-80%)ishighlydependentonthegeographicarea,thesocio-economicstatusandthenutritionalcustoms.Infectiononlyrarelycausestoxoplasmosisandusuallyclinicalsymptomsareabsent,butmayproducesevereproblemsinimmunosuppressedpersonsandfetus.Becauseonlyaprimaryinfectionduringpregnancymaybedangerousandevenfatalfortheunborn(theprobABIlityofcongenitalinfectionisabout50%),therecentonsetofaninfectionmustbeexcluded.Inpregnantwomeninover98%ofcases,theabsenceofIgMexcludesthepossibilityofrecentinfection.Innewbornstheverypresenceofanti-toxoplasmaIgMissufficienttoconfirmacongenitaltoxoplasmosis,sincematernalIgM,unlikeIgG,doesnotcrosstheplacentalbarrier.ButasignificantnumberofinfectedinfantsdonotdevelopdetectableIgMlevelsandthusarefalsenegative.Inimmunosuppressedpatientstoxoplasmosiscausesseverecomplicationsmostlybyreactivationofanearlierlatentinfection.Infectionmaybeidentifiedby

• PCR
• Indirectimmunofluorescence(IIF)
• SEROlogy:DetectionofantibodyproductionbyELISA