Neglected tropical diseases (NTDs) remain a major global public health concern, affecting an estimated 1.62 billion people in tropical and subtropical climatic zones [1,2] and accounting for approximately 200,000 deaths and 14.5 million disability-adjusted life years annually [2,3]. Although there has been a general decline in the global burden of NTDs [2], the progress is not yet on track to meet the ambitious Sustainable Development Goals 2030 target of a 90% reduction in the number of people requiring interventions for NTDs [3]. NTDs continue to pose a big challenge for low- and middle-income countries (LMICs) due to their intricate links with poverty, inadequate hygiene, poor sanitation, and limited health care access [4,5].

Poverty is a key factor exacerbating the burden of NTDs in LMICs. Financial deprivation and disease are closely intertwined, which influence the social and environmental determinants of NTDs, including water, sanitation, and hygiene, education, housing, and health care accessibility [5-7]. Poverty highly modulates the accessibility and utilization of the services related to the 5 important NTD control strategies recommended by the World Health Organization (WHO): innovative and intensified disease management; preventive chemotherapy; vector control; veterinary public health measures; and provision of safe water, sanitation, and hygiene practices [8,9]. NTDs disproportionately affect impoverished and marginalized communities, resulting in increased catastrophic health spending and out-of-pocket expenses [10]. Already living in poverty before the onset of these diseases, affected households often face deeper financial hardship as rising out-of-pocket costs push them further below the poverty line [11-13]. To manage these expenses, they often resort to coping strategies such as borrowing money or selling assets, which further exacerbates their poverty. This cycle undermines access to health care services and negatively affects treatment outcomes [13]. Physical disabilities due to NTDs, such as blindness, lesions, and swelling, may also contribute to decreased income ability [14]. This financial burden perpetuates a cycle of poverty and NTD burden, hindering service uptake and treatment [15]. Consequently, the detrimental effects of NTDs are amplified, including poor NTD-related service utilization and adherence, treatment failure, disability, and deterioration of general health and well-being [15].

Moreover, infection with NTDs increases the nutritional burden of the hosts and impedes overall health. NTDs have been reported to be associated with stunting, anemia, iron deficiency, micronutrient deficiencies, and malnutrition [16-19]. Simultaneously, nutrient deficiency may also increase the susceptibility and vulnerability of NTD-affected individuals and lead to NTD treatment failure [18,20,21]. Actions taken to control NTDs may eventually improve nutritional outcomes, which, in turn, will also influence overall health and well-being, particularly in resource-limited settings.

Despite various programs and policies implementing innovative strategies to improve NTD campaign coverage, multiple layers of poverty-associated and financial obstacles continue to hinder appropriate health-seeking behaviors in affected populations. These barriers include attending screening clinics, receiving adequate care, and treatment adherence [22-25]. Cash transfer programs have demonstrated potential for improving NTD outcomes [26-29]. These programs aim to provide small-scale monetary assistance to individuals or households to break the intergenerational cycle of poverty. Conditional cash transfers (CCTs) impart benefits through a 2-way strategy: direct cash assistance and enforced conditionalities [30]. It is also possible that conditionalities related to the control of NTDs may also impart positive effects on nutrition and overall health outcomes in LMICs. Large-scale, national-level cash transfer programs in Latin America have not only proven effective in improving social protection, economic stability, and sustained developmental outcomes [31] but have also generated interest in using cash transfers to target context-specific health outcomes, including NTD treatment outcomes, maternal health, child health, cognitive development, nutrition, and health care utilization [26,32-34].

A recent systematic review highlighted the positive impact of CCT programs in controlling NTDs. It indicated that the targeted benefits of these programs for vulnerable populations can help reduce health inequalities associated with NTDs. For example, cash transfers have been shown to reduce leprosy incidence and increase the uptake of deworming treatments in certain contexts [35]. However, the review had a major limitation in that it included and synthesized evidence for only 3 of the 21 NTDs and disease groups prioritized by WHO [2,3,35]. While other incentive programs, such as in-kind transfers, microcredits, vouchers for transport, medicines, or food, have shown the potential to promote health knowledge, reduce health inequalities, and improve health-seeking behaviors, their direct or indirect effects on NTD-related indicators have not been comprehensively studied in LMICs [36,37].

Given this context, there is a need for an evidence synthesis on the effects of cash transfers and other incentive programs on NTD-related service utilization and treatment outcomes in LMICs. This proposed systematic review and meta-analysis (depending on information availability) will conduct a comprehensive synthesis and unbiased assessment of the existing studies in this area, critically assessing the strengths and limitations of existing evidence.

The systematic review aims to answer the following three questions: (1) What are the effects of cash transfer and incentive programs on NTD-related service utilization and treatment outcomes in LMICs? (2) How do incentive program design (type, amount, and frequency), implementation plan, and other covariates influence NTD-related service utilization and treatment outcomes in LMICs? and (3) How do NTD-related service utilization and treatment outcomes influence nutritional status, overall health, and well-being in LMICs?

This protocol was developed in accordance with the guidelines of the PRISMA-P (Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols) [38]. A PRISMA-P checklist for this protocol is provided in Checklist 1. The protocol has been registered in PROSPERO (CRD42024627804).

The eligibility criteria for studies to be included in this review are adapted based on the PICOS (Population, Interventions, Comparators, Outcomes, Study Design) framework [39], as described below.

A scoping search will be conducted to identify key Medical Subject Headings terms and other relevant search terms, which will then be combined to develop a comprehensive search strategy. Boolean operators (AND, OR, and NOT), truncation/stemming (*), and phrase searching (“”) will be used. The search will focus on NTDs, using genus names along with key terms, such as cash transfer, unconditional cash transfer, CCT, microcredit, food voucher, and incentive. A preliminary search strategy is provided in Table 2.

The following databases will be searched: MEDLINE, PubMed, Scopus, Embase, Web of Science, POPLINE, Google Scholar, Cochrane Collection, PsycINFO, Global Health, EconLit, Social Sciences Citation Index, International Bibliography of the Social Sciences, Knowledge Commons of Population Council, and 3ie database. Gray literature databases, including WHO websites, AlignMNH, World Bank, and UNICEF websites, will also be searched for relevant reports. Websites and online resources of universities and research centers in LMICs will be reviewed to identify working papers, dissertations, and theses. Reference lists or bibliographies of included studies will also be hand-searched to include any additional relevant studies. For those studies not available in the public domain, a librarian will be contacted. Studies in English, published or available from 2000 to 2024, will be included. A search log will be maintained throughout the search process to document the database platforms or search interface used, the date the search was conducted, the search strings used, and the number of records or counts identified. The log will be updated as necessary to ensure transparency, robustness, and ease of updating during the study period.

Preliminary search documents will be stored in reference management software (EndNote or Mendeley). All the screened studies will be transferred into Microsoft Excel or Rayyan tool, a systematic review management platform [49].

Two reviewers will independently screen studies based on titles and abstracts. During the initial screening phase, decisions made by each reviewer will be blinded. After the initial screening is done, the studies screened by the two reviewers will be compared and checked for discrepancies. Any discrepancies in the categorization will be resolved through consultation between the reviewers or with another reviewer. A second-level independent review will then be conducted by a separate reviewer to perform quality checks on studies with discrepancies and those deemed ineligible. Studies deemed relevant based on titles and abstracts will undergo full-text screening for relevancy, following the same procedures used during the title and abstract screening phase. Reasons for the exclusion of papers will be documented. The studies will be equally divided among the reviewers for relevancy screening. Data will be extracted individually by each reviewer. Any questions arising during the process will be addressed through consultation among the reviewers to reach a consensus. Eligible studies from the full-text review will be entered directly into a master data extraction spreadsheet.

After the article screening process is completed, all eligible studies will be extracted into a master data extraction spreadsheet. The data extraction sheet will include the following categories: title, author(s), date of publication, type of publication (eg, summary, synthesis, single study), number and type of included studies (if a summary or synthesis), settings and population studied, interventions implemented, outcomes measured and results, and if relevant, whether results differed among subgroups, such as gender, socioeconomic status, or ethnicity. For studies with multiple outcomes or variables, all eligible outcomes will be extracted. The data extraction form will be pilot-tested and refined based on the information extracted from a few initial studies meeting the inclusion criteria. This process will help minimize bias and improve the validity and reliability of the systematic review. Authors will be contacted through email if key information is missing or if further information or clarification is required.

The quality assessment will be done by using the Revised Cochrane Risk of Bias for randomized trials (RoB 2) [50], the Risk of Bias in Non-Randomized Studies of Interventions (ROBINS-I) [51], the Joanna Briggs Institute (JBI) checklist for analytical cross-sectional studies, and an adapted version of the Critical Appraisal Skills Programme (CASP) [52] for qualitative studies; ecological studies will be evaluated narratively. The quality of each included study will be independently assessed by one reviewer, with the assessment results checked by a second reviewer. Any discrepancies or disagreements will be resolved through consultation with a third reviewer to reach a consensus.

Based on the initial search to develop the protocol, about 20 to 30 studies are anticipated to be included in the review [34,53,54]. This number might change during the actual work of the systematic review based on the search using electronic databases and gray literature.

A narrative synthesis will be produced by describing the studies. A geographical information system map will be generated to illustrate the frequency distribution of impact evaluations of cash transfer and incentive programs on NTD-related service utilization, treatment outcomes, nutritional status, and health and well-being, subject to data availability. Interventions of cash transfers and incentive programs will be classified into different categories for different types of NTDs, and their effects will be synthesized for (1) NTD-related service utilization; (2) treatment outcomes; and (3) nutritional status, health, and well-being outcomes. For this review, improvement in nutritional status and health and well-being are considered potential downstream or contextual outcomes that may occur through multiple pathways, in addition to through changes in NTD-related service utilization and treatment outcomes. These pathways may include independent effects of incentives on household resources, food security, health-seeking behavior, and overall living conditions. Given that most primary studies may not be designed to test the full causal pathway, causal inference in this review will be restricted to proximal outcomes (service utilization and treatment outcomes), while nutritional and broader health outcomes will be interpreted as associative and contextual. All the studies will be tabulated by quantitative and qualitative type, and key findings will be described. Primary and exploratory outcomes will be listed along with differences in effectiveness between different cash transfer and incentive programs for NTD control.

We will assess the certainty of evidence for quantitative outcomes using the GRADE (Grading of Recommendations, Assessment, Development and Evaluation) approach. For qualitative or narrative evidence, we will use an appropriate structured approach (eg, GRADE-CERQual) to evaluate confidence in the findings.

The possibility of performing a meta-analysis will be explored depending on the availability of a sufficient number of relevant studies. The ability to undertake a meta-analysis will depend on the heterogeneity of the measures, such as similarities or differences in population, intervention, outcomes, and methodologies. If a meta-analysis is deemed appropriate, statistical heterogeneity of effects will be assessed using χ² and I² statistics. Efforts will be made to analyze the factors explaining heterogeneity through moderator analysis, including subgroup meta-analysis. All analyses will be contingent on sufficient study density.

For qualitative studies, the themes will be identified using a deductive approach, and the findings will be used to interpret or complement the quantitative findings as part of the narrative synthesis. We will also consider stratifying synthesis by study design strength.

The synthesis will present the factors such as program design, implementation, context, and challenges that influence the impact of cash transfer or incentive programs on NTD-related service utilization, treatment outcomes, nutrition status, and health and well-being. Absolute evidence gaps and synthesis gaps will also be identified that can inform the development of new studies or programs.

The possibility of performing subgroup analyses will be explored. It will, however, depend on the evidence strength to summarize effects in special populations, such as pregnant women and geriatric populations, or to distinguish effect differences across different levels of groups, such as female/male, child/adolescent/adult, different geographical regions, malnourished/well-nourished, and type of disease agents (viruses, bacteria, protozoa, fungi, helminths, ectoparasites, snakebites). The effects will also be examined to determine how they vary by incentive program design (type, amount, and frequency), implementation plan, study design, and relevant covariates.

The systematic review protocol has been reviewed and approved by two independent institutional review boards: icddr,b (PR-24112) in Bangladesh and Population Council Institute (IORG0011824) in India. Although systematic reviews do not require institutional review board approvals because no human subjects were involved, these approvals were taken as an institutional requirement.

We expect that this study will be completed by April 2026. This systematic review will critically examine and provide a comprehensive assessment of the effects of cash transfer and other financial incentive programs on NTD-related service utilization and treatment outcomes in LMICs. A recent systematic review of 11 studies published in The Lancet found that CCTs improve NTD outcomes through both enhanced living standards from the cash benefits and direct health effects linked to health care–related conditionalities [35]. However, this review had a major limitation in that it included and synthesized evidence for only 3 of the 21 NTD groups prioritized by WHO. In contrast, this review will seek evidence across all 21 WHO-prioritized NTDs.

The financial impact of different categories of financial aid for mitigating NTDs will be assessed to inform policymakers about more effective intervention programs and prevention or treatment strategies. Additionally, the potential link between NTD-related service utilization and health and nutrition outcomes in LMICs will be evaluated. A methodological assessment of the published literature will be performed, and the findings will be compared with those of similar reviews to examine the strength of evidence.

The proposed systematic review will synthesize evidence generated over a 25-year period and will critically assess the strengths and limitations of existing studies on NTDs. The use of rigorous methodology and a robust article screening process is expected to ensure a comprehensive, up-to-date, and unbiased synthesis of evidence on the effectiveness of cash transfer and incentive programs in improving NTD-related service utilization, treatment outcomes, and associated health and nutrition outcomes in LMICs.

One of the major anticipated limitations of this systematic review is that the available evidence may include multiple outcome measures and substantial methodological heterogeneity, potentially limiting the feasibility of meta-analysis. Additional limitations may include potential risk of bias in the included studies, possible publication bias, language bias due to the inclusion of English-language articles only, and limitations of the search strategy. We may face limited sensitivity in the electronic database searches because of the extensive NTD-related keywords and the indexing constraints of certain databases. However, supplementary strategies, including bibliographic citation searching and snowballing from the reference lists of included articles and relevant systematic reviews, are expected to help mitigate these limitations.

This systematic review will provide policymakers with evidence to support more effective strategic planning and targeted interventions for controlling NTDs in LMICs. The findings from this systematic review will also be valuable for researchers, funding agencies, and governmental bodies seeking to design and implement effective NTD control programs.

The findings of this systematic review will be presented at national and international conferences and reported in a peer-reviewed journal in accordance with the PRISMA 2020 guideline for reporting systematic reviews [55]. Any amendments to this protocol during the review process will be documented in PROSPERO and reported in the final manuscript.