Concordance of the point-of-care circulating cathodic antigen test for the diagnosis of intestinal schistosomiasis in a low endemicity area

Background:The Kato-Katz technique is recommended worldwide for the diagnosis of intestinal schistosomiasis,detecting parasite eggs in feces of infected people.However,new tests have been developed in order to facilitate diagnosis,e.g.by detection of specific antigens secreted by schistosomes,such as the circulating cathodic antigen(CCA).The aim of this study was to evaluate the performance of the point-of-care circulating cathodic antigen test(POC-CCA)compared to the Kato-Katz technique in a low prevalence area in the Amazon Region,located in the municipality of Primavera,State of Para,Brazil.Methods:Positivity rates of the POC-CCA test and the Kato-Katz technique were calculated.The sensitivity,specificity,accuracy and kappa coefficient were determined by comparing both methods.The reference standard was established using 16 Kato-Katz slides,12 of the first fecal sample,two of the second and two of the third one.The study also included the concordance between POC-CCA results and different numbers and combinations of Kato-Katz slides.Results:The prevalence of schistosomiasis according to the reference standard or POC-CCA test reached a rate of 9.4%or 23.9%,respectively,among a total of 372 participants.The positivity rates by the Kato-Katz technique increased from 2.4 to 9.4%,according to the increase in the number of slides examined and fecal samples colleaed.A sensitivity of 55.6%,specificity 76.9%,accuracy 76%and k coefficient of 0.06 was observed by comparing one slide of the first sample and POC-CCA.Comparing 6 slides from three different samples,two slides of each,with POC-CCA resulted in a sensitivity of 583%,specificity 78.4%,accuracy 77%and k coefficient of 0.16.Finally,the comparison of 16 slides from three different samples with POC-CCA revealed a sensitivity of 65.7%,specificity 80.4%,accuracy 79%,and k coefficient of 0.27.Conclusions:The immunochromatographic test has the potential to be an important tool to combat schistosomiasis because of its practicality and applicability but should be applied with caution in low prevalence areas and in programs that aim to eliminate this disease.

High prevalence of urinary schistosomiasis in a desert population: results from an exploratory study around the Ounianga lakes in Chad

Background Researching a water-borne disease in the middle of the Sahara desert might not seem the most relevant concern.However,nomadic Sahelian pastoralists health concerns regarding their livestock and anecdotal reports about trematode infections of Fasciola spp.and Schistosoma spp.in desert-raised animals justified an exploratory study focusing on the lakes of Ounianga in Northern Chad.The aim was to test whether trematode parasites such as Schistosoma spp.occur in human populations living around the Sahara desert lakes of Ounianga Kebir and Ounianga Serir in northern Chad.Methods The study was carried out in January 2019 and comprised of three components.First,a cross sectional survey based on a random sample drawn from the population to detect infections with S.haematobium and S.mansoni;second,focus group discussions exploring disease priorities,access to health and health seeking behaviour;and third,surveying water contact sites for intermediate host snails.Samples of trematode parasites and snails were confirmed on species level by molecular genetic methods.For parasitological and malacological surveys descriptive statistics were performed.Qualitative data analysis included the full review of all transcripts,followed by a descriptive and explorative thematic analysis.Results Among 258 participants,the overall S.haematobium prevalence using urine filtration was 39.2%[95%confidence interval(CI):33.5–45.1%],with 51.5%of the infected suffering from heavy infection.The intermediate host snail of S.haematobium(Bulinus truncatus)occurred at water contact sites near both study villages,revealing the potential for local transmission.Although a positive S.mansoni point-of-care circulating cathodic antigen(POC-CCA)test result was obtained from 8.6%(95%CI 5.7–12.8%)of the samples,no intermediate host snails of S.mansoni were found,and the relevance of S.mansoni remains uncertain.Qualitative findings underline the importance of morbidity caused by urinary schistosomiasis,and the lack of access to diagnostics and treatment as a major health concern.Conclusions This research revealed a high prevalence of urinary schistosomiasis in the population living around the lakes of Ounianga in the Sahara,a United Nations Educational,Scientific and Cultural Organization(UNESCO)world heritage site in Chad.Despite the high public health importance of the associated morbidity expressed by the population,there is no access to diagnostics and treatment.Further work is needed to develop and test a context-adapted intervention.

Performance of the point-of-care circulating cathodic antigen test in the diagnosis of schistosomiasis japonica in a human cohort from Northern Samar, the Philippines

Background:Zoonotic schistosomiasis,caused by Schistosoma japonicum,remains a major public health problem in the Philippines.This study aimed to evaluate the commercially available rapid diagnostic point-of-care circulating cathodic antigen(POC-CCA)test in detecting individuals infected with S.japonicum in a human cohort from an endemic area for schistosomiasis japonica in the Philippines.Methods:Clinical samples were collectedin 18 barangays endemic for S.japonicum infection in Laoang and Palapag municipalities,Northern Samar,the Philippines,in 2015.The presence of CCA in flter-concentrated urine samples(n=412)was evaluated using the commercial kits and the results were converted to images,which were further analyzed by ImageJ software to calculate R values.The diagnostic performance of the immunochromatographic POCCCA test was compared using the Kato-Katz(KK)procedure,in-house enzyme-linked immunosorbent assays(ELISAs)and droplet digital(dd)PCR assays as reference.Results:The POC-CCA test was able to detect S.japonicum-infected individuals in the cohort with an eggs per gram of faeces(EPG)more than or equal to 10 with sensitivity/specifcity values of 63.3%/93.3%.However,the assay showed an inability to diagnose schistosomiasis japonica infections in all cohort KK-positive individuals,of which the majority had an extremely low egg burden(EPG:1–9).The prevalence of S.japonicum infection in the total cohort determined by the POC-CCA test was 12.4%,only half of that determined by the KK method(26.2%).When compared with the ELISAs and ddPCR assays as a reference,the POC-CCA assay was further shown to be a test with low sensitivity.Nevertheless,the assay exhibited signifcant positive correlations with egg burden determined by the KK technique and the target gene copy number index values determined by the ddPCR assays within the entire cohort.Conclusions:By using in silico image analysis,the POC-CCA cassette test could be converted to a quantitative assay to avoid reader-variability.Because of its low sensitivity,the commercially available POC-CCA assay had limited potential for determining the status of a S.japonicum infection in the target cohort.The assay should be applied with caution in populations where schistosome parasites(especially S.japonicum)are present at low infection intensity.