Schistosomiasis is more prevalent than previously thought: what does it mean for public health goals, policies, strategies, guidelines and intervention programs?

Abstract

Mapping and diagnosis of infections by the three major schistosome species (Schistosoma haematobium, S. mansoni and S. japonicum) has been done with assays that are known to be specific but increasingly insensitive as prevalence declines or in areas with already low prevalence of infection. This becomes a true challenge to achieving the goal of elimination of schistosomiasis because the multiplicative portion of the life-cycle of schistosomes, in the snail vector, favors continued transmission as long as even a few people maintain low numbers of worms that pass eggs in their excreta. New mapping tools based on detection of worm antigens (circulating cathodic antigen – CCA; circulating anodic antigen – CAA) in urine of those infected are highly sensitive and the CAA assay is reported to be highly specific. Using these tools in areas of low prevalence of all three of these species of schistosomes has demonstrated that more people harbor adult worms than are regularly excreting eggs at a level detectable by the usual stool assay (Kato-Katz) or by urine filtration. In very low prevalence areas this is sometimes 6- to10-fold more. Faced with what appears to be a sizable population of “egg-negative/worm-positive schistosomiasis” especially in areas of very low prevalence, national NTD programs are confounded about what guidelines and strategies they should enact if they are to proceed toward a goal of elimination. There is a critical need for continued evaluation of the assays involved and to understand the contribution of this “egg-negative/worm-positive schistosomiasis” condition to both individual morbidity and community transmission. There is also a critical need for new guidelines based on the use of these more sensitive assays for those national NTD programs that wish to move forward to strategies designed for elimination.Electronic supplementary materialThe online version of this article (doi:10.1186/s40249-017-0275-5) contains supplementary material, which is available to authorized users.

Retracted: Urinary circulating DNA and circulating antigen for diagnosis of schistosomiasis mansoni: a field study

“…In our study, KK‐microscopy showed the characteristic Schistosoma mansoni eggs in 27% of the cases. The current lower intensity of schistosomiasis in rural areas as reported by KK smear is a compelling recommendation for the use of a more sensitive test, especially if these areas are known for their low socioeconomic state and low standards of effective health education . Urine reagent strips for circulatory antigens are nowadays used as alternatives to microscopy for diagnosis of schistosomiasis.…”

“…Here, it is worth mentioning that the lower specificity of POC-CCA (19.18%) as detected in our study and confirmed in other several studies as fore-mentioned, will not prevent its application in surveys for the following reasons: First, people are more compliant to offer a urine sample rather than stool or blood [34]. Second, while Schistosoma eggs continue to be released in stool for few weeks after treatment (viable eggs 2-3 weeks and dead eggs 4-6 weeks), CCA is lowered quickly within one week after treatment; hence, it is a therapeutic monitor [31,35]. Third, the comparable cost level per test for POC-CCA and KK does not render POC-CCA expensive, especially since multiple KK tests are usually required for accurate diagnosis [32].…”

A case of paediatric bladder bilharzioma in Johannesburg, South Africa

“…This case report highlights the story of a relatively healthy‐looking child, from a rural background, harboring a hidden debilitating disease that was only picked up on cystoscopy. Multiple tests of urine microscopy for parasite eggs were unsurprisingly negative as it is known to have high specificity but low sensitivity . The primary healthcare center did not suspect bilharzia, and no empiric treatment was administered.…”

“…Multiple tests of urine microscopy for parasite eggs were unsurprisingly negative as it is known to have high specificity but low sensitivity. 7 The primary healthcare center did not suspect bilharzia, and no empiric treatment was administered.…”

A library of cell-surface and secreted proteins fromSchistosoma mansoniidentifies early serological markers of infection

“…The exact prevalence of schistosomiasis worldwide may be underestimated because of the limitations of routine methods of detection [7]. Diagnosis of S. mansoni infections and subsequent decisions on mass drug administration mainly rely on observing parasite eggs in the stools of patients: the Kato-Katz test.…”