Comparison of novel and standard diagnostic tools for the detection of Schistosoma mekongi infection in Lao People’s Democratic Republic and Cambodia

Background:Given the restricted distribution of Schistosoma mekongi in one province in Lao People’s Democratic Republic(Lao PDR)and two provinces in Cambodia,together with progress of the national control programmes aimed at reducing morbidity and infection prevalence,the elimination of schistosomiasis mekongi seems feasible.However,sensitive diagnostic tools will be required to determine whether elimination has been achieved.We compared several standard and novel diagnostic tools in S.mekongi-endemic areas.Methods:The prevalence and infection intensity of S.mekongi were evaluated in 377 study participants from four villages in the endemic areas in Lao PDR and Cambodia using Kato-Katz stool examination,antibody detection based on an enzyme-linked immunosorbent assay(ELISA)and schistosome circulating antigen detection by lateral-flow tests.Two highly sensitive test systems for the detection of cathodic and anodic circulating antigens(CCA,CAA)in urine and serum were utilized.Results:Stool microscopy revealed an overall prevalence of S.mekongi of 6.4%(one case in Cambodia and 23 cases in Lao PDR),while that of Opisthorchis viverrini,hookworm,Trichuris trichiura,Ascaris lumbricoides and Taenia spp.were 50.4%,28.1%,3.5%,0.3%and 1.9%,respectively.In the urine samples,the tests for CCA and CAA detected S.mekongi infections in 21.0%and 38.7%of the study participants,respectively.In the serum samples,the CAA assay revealed a prevalence of 32.4%,while a combination of the CAA assay in serum and in urine revealed a prevalence of 43.2%.There was a difference between the two study locations with a higher prevalence reached in the samples from Lao PDR.Conclusions:The CCA,CAA and ELISA results showed substantially higher prevalence estimates for S.mekongi compared to Kato-Katz thick smears.Active schistosomiasis mekongi in Lao PDR and Cambodia might thus have been considerably underestimated previously.Hence,sustained control efforts are still needed to break transmission of S.mekongi.The pivotal role of highly sensitive diagnostic assays in areas targeting elimination cannot be overemphasised.

Utilizing the ultrasensitive Schistosoma up-converting phosphor lateral flow circulating anodic antigen(UCP-LF CAA)assay for sample pooling-strategies

Background:Methodological applications of the high sensitivity genus-specific Schistosoma CAA strip test,allowing detection of single worm active infections(ultimate sensitivity),are discussed for efficient utilization in sample pooling strategies.Besides relevant cost reduction,pooling of samples rather than individual testing can provide valuable data for large scale mapping,surveillance,and monitoring.Method:The laboratory-based CAA strip test utilizes luminescent quantitative up-converting phosphor(UCP)reporter particles and a rapid user-friendly lateral flow(LF)assay format.The test includes a sample preparation step that permits virtually unlimited sample concentration with urine,reaching ultimate sensitivity(single worm detection)at 100%specificity.This facilitates testing large urine pools from many individuals with minimal loss of sensitivity and specificity.The test determines the average CAA level of the individuals in the pool thus indicating overall worm burden and prevalence.When requiring test results at the individual level,smaller pools need to be analysed with the pool-size based on expected prevalence or when unknown,on the average CAA level of a larger group;CAA negative pools do not require individual test results and thus reduce the number of tests.Results:Straightforward pooling strategies indicate that at sub-population level the CAA strip test is an efficient assay for general mapping,identification of hotspots,determination of stratified infection levels,and accurate monitoring of mass drug administrations(MDA).At the individual level,the number of tests can be reduced i.e.in low endemic settings as the pool size can be increased as opposed to prevalence decrease.Conclusions:At the sub-population level,average CAA concentrations determined in urine pools can be an appropriate measure indicating worm burden.Pooling strategies allowing this type of large scale testing are feasible with the various CAA strip test formats and do not affect sensitivity and specificity.It allows cost efficient stratified testing and monitoring of worm burden at the sub-population level,ideally for large-scale surveillance generating hard data for performance of MDA programs and strategic planning when moving towards transmission-stop and elimination.

Selecting accurate post-elimination monitoring tools to prevent reemergence of urogenital schistosomiasis in Morocco:a pilot study

Background:After alleged stop of transmission of schistosomiasis and further down the line in post elimination settings,sensitive tools are required to monitor infection status to prevent potential re-emergence.In Rahala,where transmission cycle of Schistosoma haematobium is interrupted since 2004 but where 30%of snails are still infected by S.bovis,potential human S.bovis infection can’t be excluded.As methods based on egg-counts do not provide the required sensitivity,antibody or antigen assays are envisaged as the most appropriate tools for this type of monitoring.Methods:In this pilot study,the performances of three assays were compared:two commercially available antibody tests(ELISA and haemagglutination format)indicating exposure,and an antigen test(lateral flow strip format)demonstrating active infection.All 37 recruited study participants resided in Rahala(Akka,province Tata,Morocco).Participants had been diagnosed and cured from schistosomiasis in the period between 1983 and 2003.In 2015 these asymptomatic participants provided fresh clinical samples(blood and urine)for analysis with the aforementioned diagnostics tests.Results:No eggs were identified in the urine of the 37 participants.The haemagglutination test indicated 6 antibody positives whereas the ELISA indicated 28 antibody positives,one indecisive and one false positive.ELISA and haemagglutination results matched for 18 individuals,amongst which 5 out of 6 haemagglutination positives.With the antigen test(performed on paired serum and urine samples),serum from two participants(cured 21 and 32 years ago)indicated the presence of low levels of the highly specific Schistosoma circulating anodic antigen(CAA),demonstrating low worm level infections(less than 5 pg/ml corresponding to probably single worm pair).One tested also CAA positive with urine.ELISA indicated the presence of human anti-Schistosoma antibodies in these two CAA positive cases,haemagglutination results were negative.Conclusions:To prevent reemergence of schistosomiasis in Morocco current monitoring programs require specific protocols that include testing of antibody positives for active infection by the UCP-LF CAA test,the appropriate diagnostic tool to identify Schistosoma low grade infections in travelers,immigrants and assumed cured cases.The test is genus specific will also identify infections related to S.bovis.