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

Abstract

BackgroundAfter 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.MethodsIn 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.ResultsNo 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.ConclusionsTo 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s40249-017-0289-z) contains supplementary material, which is available to authorized users.

Survey and Diagnostic Challenges after Transmission-Stop: Confirming Elimination of Schistosomiasis haematobium in Morocco

“…However, antibody testing for travelers, immigrants and residents born before transmission stop was claimed does not seem to be a valid approach as there are no accurate antibody tests that can distinguish past from previous infection. Moreover, sensitivity as well as specificity of the current antibody assays may be an issue [21,13]. Relevantly large inconsistencies between results obtained with different antibody tests still make the general application of a single antibody test challenging [22].…”

“…In 2017, small study amongst 37 adults with a history of past infection (before 2004) indicated 2 individuals still carrying residual but low worm burden Schistosoma infections; the actual involved species was not determined [13]. e applied diagnostic tool detected a wormspecific carbohydrate which is discharged by alive worms into the human blood circulation, the circulating anodic antigen (CAA).…”

“…e CAA test is a highly specific and the most sensitive assay capable to detect a single worm Schistosoma infection including non-fecund or singlesex worms. It is a genus specific test that will identify active infections with any of the know Schistosoma species, including bovis, curassoni and intercalatum [13]. e identification of the two individuals with residual infection indicates the importance of the need of proper and highly sensitive diagnostic tools to obtain accurate information regarding elimination status.…”

“…for dried blood samples [42], serum, plasma and urine [11][12][13]. e test includes a sample preparation step which may make the assay in its current format somewhat less field-friendly as this step requires some basic laboratory equipment.…”

“…e status of schistosomiasis in areas that have reached low-transmission was reviewed not long ago [6] and recommendations offered regarding tools and strategies for monitoring, criteria to determine interruption of transmission and validation of elimination. However, these recommendations do not (yet) include the implementation of the newly developed ultrasensitive diagnostic tools [7,8] that allow highly accurate determination of the infection status [9][10][11][12][13][14][15]. It is believed that transmission-stop has been achieved in 19 countries, and currently some already await confirmation of successful steep towards elimination.…”