wechosetousethe samepretreatmentproceduresasusedinthestudiesinnearby
endemicareas(Polmanetal.1995,1998).However,forurine CCA detection, we cross-checked by submitting each series of samples also to the alternative pretreatment method.
Circulating anodic antigen (CAA) in serum and circulating cathodic antigen (CCA) levels in serum and urine were deter- minedbyELISA(Deelderetal.1989;DeJongeetal.1990). Antigen concentrations were calculated with a four parametric curve fitting method, using a standard dilution curve of the TCA-soluble fraction of schistosome adult worm antigen (AWA-TCA), which contains approximately 3% (w/w) CAA and 3% (w/w) CCA.
The lower detection limit of the serum CAA ELISA was ap- proximately1 ng/ml of AWA-TCA (= 0.03 ng CAA/ml).The cut-off value for this ELISA is equal to the lower detection limit of the assay both after pretreatment with TCA and after alka- line/heating(Krijgeret al.1994).Serumsamplesweretestedin twofolddilutionseriesataninitialdilutionof1:4.UrineCAA levels were not determined in this study, as results with CAA detection in urine have so far been relatively poor (Polman etal.1995,1998).
The lower detection limit of the CCA ELISA was approxi- mately2ng/mlofAWA-TCA(=0.06ngCCA/ml).Thecut-off value for the urine CCA ELISA (based on 102 Dutch control urine samples) is equal to 2.46 ng CCA/ml after pretreatment with TCA, and equal to the lower detection limit after pre- treatmentwithalkaline/heating.FortheserumCCAELISA, the cut-off values (based on106 Dutch control sera) are1.52 ng CCA/ml after pretreatment with alkaline/heating and 1.14 ng CCA/ml afterTCA pretreatment, respectively (Krijger et al. 1994).Samplesweretestedintwofolddilutionseries,atanin- itial dilution of 1 : 4 (urines pretreated with TCA and sera) or 1:2(urinespretreatedwithalkaline/heating).
Results
NoneoftheindividualsfromBurundiorSenegalhadS.man- soni eggs in their stools, neither with the Kato-Katz nor with theSSForVisserfiltermethod.NoS.haematobiumeggswere found in the urine samples from Senegal.
The circulating antigen detection results are presented in Table 1.All individualswere negative forserumCAA,except oneinBurundi.Thispositiveserumwasfroma15-year-oldboy with no specific characteristics; the level was 0.16 ng/ml CAA, justabovethecut-offlevel.ForserumCCA,30falsepositives werefoundinBurundiand10inSenegal;forurineCCA,91 false positives were found in Burundi and two in Senegal.The specificityoftheserumCAAELISAwasthus99%inBurundi and100%inSenegal.FortheserumCCAELISAthespecificity was 92.3% in Senegal (with TCA pretreatment) and 69.4% in Burundi(withalkaline/heating).FortheurineCCAELISA, thespecificitywas98.5%inSenegal(TCA)andonly15.7%in Burundi(alkaline/heating).Afterswitchingthepretreatment
wechosetousethe samepretreatmentproceduresasusedinthestudiesinnearbyendemicareas(Polmanetal.1995,1998).However,forurine CCA detection, we cross-checked by submitting each series of samples also to the alternative pretreatment method.Circulating anodic antigen (CAA) in serum and circulating cathodic antigen (CCA) levels in serum and urine were deter- minedbyELISA(Deelderetal.1989;DeJongeetal.1990). Antigen concentrations were calculated with a four parametric curve fitting method, using a standard dilution curve of the TCA-soluble fraction of schistosome adult worm antigen (AWA-TCA), which contains approximately 3% (w/w) CAA and 3% (w/w) CCA.The lower detection limit of the serum CAA ELISA was ap- proximately1 ng/ml of AWA-TCA (= 0.03 ng CAA/ml).The cut-off value for this ELISA is equal to the lower detection limit of the assay both after pretreatment with TCA and after alka- line/heating(Krijgeret al.1994).Serumsamplesweretestedin twofolddilutionseriesataninitialdilutionof1:4.UrineCAA levels were not determined in this study, as results with CAA detection in urine have so far been relatively poor (Polman etal.1995,1998).The lower detection limit of the CCA ELISA was approxi- mately2ng/mlofAWA-TCA(=0.06ngCCA/ml).Thecut-off value for the urine CCA ELISA (based on 102 Dutch control urine samples) is equal to 2.46 ng CCA/ml after pretreatment with TCA, and equal to the lower detection limit after pre- treatmentwithalkaline/heating.FortheserumCCAELISA, the cut-off values (based on106 Dutch control sera) are1.52 ng CCA/ml after pretreatment with alkaline/heating and 1.14 ng CCA/ml afterTCA pretreatment, respectively (Krijger et al. 1994).Samplesweretestedintwofolddilutionseries,atanin- itial dilution of 1 : 4 (urines pretreated with TCA and sera) or 1:2(urinespretreatedwithalkaline/heating).ResultsNoneoftheindividualsfromBurundiorSenegalhadS.man- soni eggs in their stools, neither with the Kato-Katz nor with theSSForVisserfiltermethod.NoS.haematobiumeggswere found in the urine samples from Senegal.The circulating antigen detection results are presented in Table 1.All individualswere negative forserumCAA,except oneinBurundi.Thispositiveserumwasfroma15-year-oldboy with no specific characteristics; the level was 0.16 ng/ml CAA, justabovethecut-offlevel.ForserumCCA,30falsepositives werefoundinBurundiand10inSenegal;forurineCCA,91 false positives were found in Burundi and two in Senegal.The specificityoftheserumCAAELISAwasthus99%inBurundi and100%inSenegal.FortheserumCCAELISAthespecificity was 92.3% in Senegal (with TCA pretreatment) and 69.4% in Burundi(withalkaline/heating).FortheurineCCAELISA, thespecificitywas98.5%inSenegal(TCA)andonly15.7%in Burundi(alkaline/heating).Afterswitchingthepretreatment
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