Parasite Population Genetic Contributions to the Schistosomiasis Consortium for Operational Research and Evaluation within Sub-Saharan Africa

Abstract

. Analyses of the population genetic structure of schistosomes under the “Schistosomiasis Consortium for Operational Research and Evaluation” (SCORE) contrasting treatment pressure scenarios in Tanzania, Niger, and Zanzibar were performed to provide supplementary critical information with which to evaluate the impact of these large-scale control activities and guide how activities could be adjusted. We predicted that population genetic analyses would reveal information on a range of important parameters including, but not exclusive to, recruitment and transmission of genotypes, occurrence of hybridization events, differences in reproductive mode, and degrees of inbreeding, and hence, the evolutionary potential, and responses of parasite populations under contrasting treatment pressures. Key findings revealed that naturally high levels of gene flow and mixing of the parasite populations between neighboring sites were likely to dilute any effects imposed by the SCORE treatment arms. Furthermore, significant inherent differences in parasite fecundity were observed, independent of current treatment arm, but potentially of major impact in terms of maintaining high levels of ongoing transmission in persistent “biological hotspot” sites. Within Niger, naturally occurring Schistosoma haematobium/Schistosoma bovis viable hybrids were found to be abundant, often occurring in significantly higher proportions than that of single-species S. haematobium infections. By examining parasite population genetic structures across hosts, treatment regimens, and the spatial landscape, our results to date illustrate key transmission processes over and above that which could be achieved through standard parasitological monitoring of prevalence and intensity alone, as well as adding to our understanding of Schistosoma spp. life history strategies in general.

Impact of Different Mass Drug Administration Strategies for Gaining and Sustaining Control of Schistosoma mansoni and Schistosoma haematobium Infection in Africa

“…19 A subset of communities in the gaining control studies were also used for the companion studies of intermediate host snail abundance and infection 20 and the influence of MDA on population genetics of the respective Schistosoma parasites. 21 Midpoint structural reorganization of the Niger gaining and sustaining control studies. In the gaining and sustaining control studies in Niger, there was a significant protocol deviation with respect to randomization of study communities, in which geographically clustered groups of 25 communities were randomly assigned to each of the study arms rather than having the different community interventions distributed randomly.…”

Application of Schistosomiasis Consortium for Operational Research and Evaluation Study Findings to Refine Predictive Modeling of Schistosoma mansoni and Schistosoma haematobium Control in Sub-Saharan Africa

“…The second SCORE modeling article examined the effects of adding schistosome mating and density-dependence factors 36 on the rates of transmission within endemic locations, as predicted by the SWB model and older MWB models. The analysis identified some inherent inconsistencies in the MWB models, in part because the observed "wormy person" aggregation phenomenon, 37 in which a few individuals carry a disproportionally high number of worms, is likely to be different between children and adults.…”

SCORE Operational Research on Moving toward Interruption of Schistosomiasis Transmission

“…9 Interventions were conducted for 5 years, starting in 2012 and ending in 2017. 14 The main study outcomes were prevalence and intensity at Year 6 (2017) among 9-to 12-year-old children. 15 Annually, efforts were made to survey 100 children aged 9-12 years in each of the 90 study schools with a single urine filtration for the presence and number of S. haematobium eggs.…”

“…Additional results available in other publications include urine prevalence and intensity among adults, first-year students at the baseline and at the end point, and schistosome population genetics. [14][15][16] Mass drug administration. Biannual MDA was conducted by the NTD Program of the Ministry of Health Zanzibar, according to the National Plan.…”

“…The significance of these hybrids for human health and future elimination efforts remains to be determined. 14 Parasitologic results. The baseline prevalence of S. haematobium in 9-to 12-year-old children was 24.8%, 10.1%, 13.9%, and 15.9%, in arms 1, 2, 3, and 4, respectively (Figure 3).…”