This systematic review reports on the progress in the control of STH infections, specifically those caused by A. lumbricoides, T. trichiura, and hookworm, from 2000 to 2023. The study reports on data extracted from 310 papers, which provided quantitative information on the burden of STH infection stratified by year, region, and age group. A significant proportion of the studies focused on SAC, reflecting the current WHO guidelines for treatment and monitoring plus evaluation.
Several diagnostics were used, including direct microscopy and FECT among others, despite WHO recommendations for the use of KK as the standard for monitoring and evaluation (M&E) of STH infections [14, 15]. The use of varied techniques can result in differences in the measurement of prevalence and intensity. Furthermore, only a small proportion of studies looked at the intensity of infection. Variability in age classification across studies also affected comparisons. Additionally, non-validated treatment reports may lead to an overestimation of MDA implementation coverage.
STH M&E programmes need to address both the inconsistencies in age group classification and standardization of diagnostic methods, particularly in low-prevalence settings. WHO recommends the KK method as choice of diagnostic and survey in SAC as a proxy indicator, without disaggregating data by age or sex [16]. An effective M&E programme should be comprehensive (including prevalence, intensity, demographic, and treatment data), focusing on robust data collection (based on adequate sample size, quality control process, and highly sensitive and specific diagnostic techniques), cost-effectiveness (determining the best value for resources spent), and community involvement. By standardizing M&E protocols and investing in capacity-building, a significant impact could be made in the fight against STHs and improving health outcomes in Ethiopia over the coming decade.
The overall A. lumbricoides prevalence dropped from 13.8% to 9.4% (Table S1) over the last decade, indicating the effectiveness of the SAC-based deworming policy, which was launched in 2001 [17], and improvements in WaSH services in the country. Deworming projects were carried out in many parts of Ethiopia over the study period, which were enhanced by the launch of a national deworming programme in 2015, enabling the distribution of an estimated 92.7 million treatments for STHs [18]. Prevalence was substantially reduced in the Amhara region, which experienced a decrease of 54.8% between 2015 and 2019. This reduction can potentially be attributed to high and sustained MDA coverage and improved programmatic follow-up. However, a mixed picture emerged in other regions like Tigray and Oromia, which showed non-significant reductions. This may be due to differences in programme commitment, baseline endemicity, and population movement that may have impacted these regional patterns. Additionally, an increasing trend was noted in the Southern region, despite relatively improved reported stability. These factors may highlight challenges specific to implementation quality, coverage consistency, or data reporting in that region, underscoring the need for more targeted investigations into programme gaps and regional disparities.
Community-based estimates of the prevalence of infection showed a significant reduction for A. lumbricoides, which declined from 20.0% before 2015 to 8.1% between 2015 and 2019. This reflects the benefit of deworming and WaSH activities in other groups not targeted by MDA, as the overall worm burden decreased, thereby reducing the risk of exposure [19] (the indirect benefits to untreated groups generated by treatment in other population groupings). Despite this, the prevalence among SAC showed a non-significant increase after 2020, suggesting that further efforts are required to increase MDA coverage and improve the integration of treatment with other interventions such as WaSH improvements to further reduce transmission and sustain the results achieved by MDA. The prevalence among pre-SAC increased between 2015 and 2019, but decreased after 2020. This highlights the need for treating this age group in combination with SAC.
The intensity of A. lumbricoides infection did not show a significant change despite the reduction in prevalence. This could be due to the aggregation of parasites in certain groups, and with a few individuals harbouring a higher number of eggs, as the prevalence decreases, especially in untreated adults. As prevalence decreases, the aggregation of worms within the human population increases, leading to hotspots of infection in a few individuals [20]. This indicates the importance of both identifying individuals with high numbers of eggs and treating adult age groups to enhance control impact.
The impact of deworming interventions was not evident in the prevalence of T. trichiura, which exhibited a non-significant reduction from 5.1% before 2015 to 3.0% after 2020, as indicated by the high k value. This suggests the limitation of MDA interventions for this parasite, given the low efficacy of albendazole and mebendazole for this STH species. Several studies have reported lower efficacy of albendazole and mebendazole for T. trichiura [21,22,23,24].
This finding was in line with a recent meta-analysis study, which found minimal reduction of T. trichiura among children and adolescents [25, 26]. However, one systematic review conducted in Ethiopia [27] reported a significant reduction in this species. A small reduction in T. trichiura prevalence in this review suggests the need to incorporate WaSH services to further decrease the transmission and also to consider what drug combinations might effectively treat T. trichiura infection [28].
The reduction in prevalence for T. trichiura was greatest in the Southern region between 2015 and 2019, but an increase was observed after 2020, potentially related to missed MDA rounds due to national remapping activities and the COVID-19 pandemic, which redirected the focus and resources of the Ethiopian health system.
A consistent reduction in T. trichiura prevalence was found in the Amhara region, but changes in Oromia and Tigray were not significant. This highlights regional differences in the implementation of the MDA programme, potentially attributed to factors such as proper planning, logistic management, conflict, and the rapidly growing population that influences drug demand.
There was a non-significant reduction in the prevalence of T. trichiura in both the SAC and the community groups, though the prevalence in the community increased after 2020. No changes were seen in pre-SAC during either period. This highlights that exposure outside of SAC is common and supports the need to reconsider control strategies. Additionally, a study conducted in Indonesia reported a high prevalence of T. trichiura infection among pre-SAC [29].
The intensity of T. trichiura infections varies over time, with a gradual and non-significant increase observed across the periods. This indicates ongoing transmission and increasing morbidity caused by the worms (Table S1).
The overall rate of hookworm infection saw a non-significant reduction. This may be influenced by several factors, including the limited efficacy of albendazole or mebendazole compared to A. lumbricoides [30, 31]. Additionally, even with ongoing MDA, transmission could be facilitated by the ability of hookworm larvae to stay in the environment for longer periods [32]. Furthermore, variation is found in the epidemiology and complexity of helminth infections, with hookworm infection peaks and plateaus in the adult age groups [33]. As such, MDA targeting SAC is less likely to make a significant impact on this parasite [34]. This, in general, highlights the need for integration of interventions with WaSH improvements.
Regionally, the prevalence of hookworm showed a substantial reduction in the Amhara region between 2015 and 2019, with a decrease from 16.3% to 9.9%. The other regions had mixed outcomes, with no significant changes recorded.
The variation in hookworm prevalence by age group, where SAC saw decreases but an increasing trend was seen in the general community, highlights the need to involve adults in MDA treatment. This agrees with a systematic review from the Philippines, which reports a limited effect of chemotherapy among adults [34].
The mean hookworm egg count increased steadily across the various periods, attributable to active transmission and ineffective deworming efforts targeting SAC (Table S1). This is in line with several studies reporting that the transmission dynamics of hookworm were higher among adults [35,36,37]. Hence, extending deworming to include this group increases the effectiveness of control strategies.
The findings from the systematic review suggest that M&E activities should target all age groups, not just SAC, with enhanced MDA treatment coverage data, which is verified by coverage surveys. In addition, progress has been made in reducing the prevalence and intensity of STHs, but a comprehensive intervention is crucial to sustaining gains. This includes higher MDA coverage levels, expanding treatment to the whole community, including adults, but also improvement in WaSH services to address reinfection.
There were a limited number of published papers documenting STH infection levels in Gambella, Somali, Afar, Benishangul, Dire Dawa, Addis Abeba, and Harari, hindering comprehensive comparisons of trends in other regions of Ethiopia. Additionally, the significant heterogeneity regarding methodology, population groups, diagnostic methods, sampling strategies, and classifications of geographical settings may impact the comparisons of data gathered from different studies, despite employing random-effects analysis to account for variability. Furthermore, data on the intensity of infection, as opposed to prevalence, were scarce.