Precision mapping of schistosomiasis and soil-transmitted helminthiasis among school age children at the coastal region, Kenya

Priority knowledge gaps for schistosomiasis research and development in the World Health Organization Africa Region

Schistosomiasis, also known as bilharzia, is a widespread neglected tropical disease (NTD) in Africa, with more significant research and development (R&D) challenges and gaps compared to other preventive chemotherapy NTDs (PC-NTDs) like onchocerciasis, lymphatic filariasis, and trachoma. In response to this challenge, some global initiatives have advocated for bridging this gap, focusing on coordinated engagement with research donors. In this opinion article we highlight key R&D priorities for combating schistosomiasis in the WHO Africa region. These include defining morbidity indicators, expanding prevention, and developing innovative diagnostics, treatments, and public health strategies like test-and-treat. We emphasize integrating efforts with broader health campaigns, assessing zoonotic transmission through One Health, and using environmental surveillance tools like xenomonitoring and eDNA. We stress the need to study climate and environmental impacts on transmission, zoonotic transmission, schistosome hybridization, and snail ecology, advancing snail control, and developing vaccines, while calling for new treatments beyond praziquantel, addressing drug resistance, and improving access for children and remote populations. Further, operational research should refine hotspot interventions, enhance water, sanitation and hygiene integration, and address socio-cultural barriers. Lastly, sustainable funding and global collaboration are vital to achieve 2030 NTD Roadmap goals.

Better floors, better health: a theory of change for an improved household flooring intervention in rural communities in Kwale and Bungoma counties, Kenya

BACKGROUND

Household flooring is increasingly being investigated as a determinant of health, however the pathways through which flooring may impact health and wellbeing are not yet well understood. The SABABU study is a cluster-randomised controlled trial evaluating the impact of an improved flooring intervention on soil-transmitted helminthiasis, tungiasis, and enteric infections in Bungoma and Kwale counties, Kenya. This paper presents the findings from a theory of change development process that was undertaken as part of the formative research phase of the SABABU project.

METHODS

A co-creation workshop (n = 1), stakeholder meetings (n = 2), and community meetings (n = 2) were held with a range of participants including community members (n = 36), village-level leaders (n = 28), and local government stakeholders (n = 14) to draft and refine the theory of change framework. These meetings were informed by a previous formative research phase conducted in study communities - comprised of household observations, in-depth interviews, and focus group discussions with community members - to investigate daily routines, use of space within homes, and attitudes towards home improvement.

RESULTS

The theory of change framework demonstrates how the improved household flooring intervention aims to reduce prevalence of soil-transmitted helminthiasis, enteric infections and tungiasis and improve psychological wellbeing among children and caregivers. Reductions in infections are predicated on limited contact between improved floors and animals, regular floor cleaning, and household members conducting their daily routines on the new floors. Gains in psychological wellbeing are tied to increased feelings of pride, self-efficacy, and social progress, as well as improved quality of life through reduced morbidity from enteric and parasitic infections.

CONCLUSION

This study presents a theory of change framework mapping the pathways through which an improved flooring intervention may impact health and wellbeing. The results can be of use to researchers or programmes that are in the design or evaluation phase of a household flooring project in Kenya or other settings where access to improved floors is limited.

Effectiveness of Three Sampling Approaches for Optimizing Mapping and Preventive Chemotherapy against Schistosoma mansoni in the Western Part of Côte d'Ivoire

The elimination of schistosomiasis as a public health problem by 2030 is one of the main goals put forth in the World Health Organization's roadmap for neglected tropical diseases. This study aimed to compare different sampling approaches to guide mapping and preventive chemotherapy. A cross-sectional parasitological survey was conducted from August to September 2022 in the health districts of Biankouma, Ouaninou, and Touba in the western part of Côte d'Ivoire. The prevalence and intensity of Schistosoma mansoni infection were assessed in children aged 5-14 years using three sampling approaches. The first approach involved a random selection of 50% of the villages in the health districts. The second approach involved a random selection of half of the villages selected in approach 1, thus constituting 25% of the villages in the health district. The third approach consisted of randomly selecting 15 villages from villages selected by approach 2 in each health district. The overall prevalence of S. mansoni was 23.5% (95% confidence interval (CI): 19.9-27.6%), 21.6% (95% CI: 17.1-26.8%), and 18.3% (95% CI: 11.9-27.1%) with the first, second, and third approach, respectively. The respective geometric mean S. mansoni infection intensity was 117.9 eggs per gram of stool (EPG) (95% CI: 109.3-127.3 EPG), 104.6 EPG (95% CI: 93.8-116.6 EPG), and 94.6 EPG (95% CI 79.5-112.7 EPG). We conclude that, although randomly sampling up to 50% of villages in a health district provides more precise population-based prevalence and intensity measures of S. mansoni, randomly selecting only 15 villages in a district characterized by low heterogeneity provides reasonable estimates and is less costly.

Re-assessment of schistosomiasis in nine endemic districts with cluster sampling in Sierra Leone

Background

Baseline mapping showed that schistosomiasis was highly/moderately endemic in nine districts in Sierra Leone. Mass drug administration (MDA) with praziquantel started in 2009, and after multiple rounds of treatment, an impact assessment was conducted in 2016 followed by a second re-assessment in 2022 using cluster sampling to provide more granular data for refining chiefdom (sub-district) treatment strategies.

Methods

On average, 20 rural villages were systematically selected per district by probability proportional to population size across the nine districts. Surveys were conducted in schools, and 24 school children aged between 5 and 14 years were randomly selected, with an equal number of boys and girls. One stool sample and one urine sample were collected per child. Two Kato-Katz slides were examined per stool for Schistosoma mansoni infection. Hemastix strips were used as a proxy for S. haematobium infection with urine filtration used for egg counts on hematuria-positive samples.

Results

In total, 4,736 stool samples and 4,618 urine samples were examined across 200 schools in 125 chiefdoms. Overall, the prevalence of S. mansoni was 16.3% (95% CI: 15.3-17.4%), while the overall prevalence of S. haematobium was 2.0% (95% CI: 1.6-2.4%) by hematuria. The prevalence of heavy infections for S. mansoni and S. haematobium was 1.5% (95% CI: 1.1-1.9%) and 0.02% (95% CI: 0.0-0.14%), respectively. Among 125 chiefdoms surveyed, the overall schistosomiasis prevalence was <10% in 65 chiefdoms, 10-49.9% in 47 chiefdoms, and ≥ 50% in 13 chiefdoms. There was a mixed relationship between schistosomiasis in school children and WASH access in schools.

Conclusion

Sierra Leone has made significant progress in reducing schistosomiasis prevalence across the country after a decade of MDA intervention. However, high prevalence remains in some hotspot chiefdoms. The next steps are for the national program to investigate and address any potential issues such as low coverage or poor knowledge of schistosomiasis risk behaviors and, where appropriate, consider broadening to community-wide treatment in hotspot chiefdoms or communities.

Enabling targeted mass drug administration for schistosomiasis in north-western Tanzania: Exploring the use of geostatistical modeling to inform planning at sub-district level

INTRODUCTION

Schistosomiasis is a parasitic disease in Tanzania affecting over 50% of the population. Current control strategies involve mass drug administration (MDA) campaigns at the district level, which have led to problems of over- and under-treatment in different areas. WHO guidelines have called for more targeted MDA to circumvent these problems, however a scarcity of prevalence data inhibits decision makers from prioritizing sub-district areas for MDA. This study demonstrated how geostatistics can be used to inform planning for targeted MDA.

METHODS

Geostatistical sub-district (ward-level) prevalence estimates were generated through combining a zero-inflated poisson model and kriging approach (regression kriging). To make predictions, the model used prevalence survey data collected in 2021 of 17,400 school children in six regions of Tanzania, along with several open source ecological and socio-demographic variables with known associations with schistosomiasis.

RESULTS

The model results show that regression kriging can be used to effectively predict the ward level parasite prevalence of the two species of Schistosoma endemic to the study area. Kriging was found to further improve the regression model fit, with an adjusted R-squared value of 0.51 and 0.32 for intestinal and urogenital schistosomiasis, respectively. Targeted treatment based on model predictions would represent a shift in treatment away from 193 wards estimated to be over-treated to 149 wards that would have been omitted from the district level MDA.

CONCLUSIONS

Geostatistical models can help to support NTD program efficiency and reduce disease transmission by facilitating WHO recommended targeted MDA treatment through provision of prevalence estimates where data is scarce.

Optimal control analysis of a transmission interruption model for the soil-transmitted helminth infections in Kenya

Kenya is among the countries endemic for soil-transmitted helminthiasis (STH) with over 66 subcounties and over 6 million individuals being at-risk of infection. Currently, the country is implementing mass drug administration (MDA) to all the at-risk groups as the mainstay control strategy. This study aimed to develop and analyze an optimal control (OC) model, from a transmission interruption model, to obtain an optimal control strategy from a mix of three strategies evaluated. The study used the Pontryagin's maximum principle to solve, numerically, the OC model. The analysis results clearly demonstrated that water and sanitation when implemented together with the MDA programme offer the best chances of eliminating these tenacious and damaging parasites. Thus, we advocate for optimal implementation of the combined mix of the two interventions in order to achieve STH elimination in Kenya, and globally, in a short implementation period of less than eight years.

Infection with soil-transmitted helminths and their impact on coinfections

The most important soil-transmitted helminths (STHs) affecting humans are roundworms, whipworms, and hookworms, with a large proportion of the world's population infected with one or more of these intestinal parasites. On top of that, concurrent infections with several viruses, bacteria, protozoa, and other helminths such as trematodes are common in STH-endemic areas. STHs are potent immunomodulators, but knowledge about the effects of STH infection on the direction and extent of coinfections with other pathogens and vice versa is incomplete. By focusing on Kenya, a country where STH infections in humans are widespread, we provide an exemplary overview of the current prevalence of STH and co-occurring infections (e.g. with Human Immunodeficiency Virus, Plasmodium falciparum, Giardia duodenalis and Schistosoma mansoni). Using human data and complemented by experimental studies, we outline the immunomechanistic interactions of coinfections in both acutely STH transmigrated and chronically infected tissues, also highlighting their systemic nature. Depending on the coinfecting pathogen and immunological readout, STH infection may restrain, support, or even override the immune response to another pathogen. Furthermore, the timing of the particular infection and host susceptibility are decisive for the immunopathological consequences. Some examples demonstrated positive outcomes of STH coinfections, where the systemic effects of these helminths mitigate the damage caused by other pathogens. Nevertheless, the data available to date are rather unbalanced, as only a few studies have considered the effects of coinfection on the worm's life cycle and associated host immunity. These interactions are complex and depend largely on the context and biology of the coinfection, which can act in either direction, both to the benefit and detriment of the infected host.