Reducing Malaria Transmission in Forest-going Mobile and Migrant Populations in Lao PDR and Cambodia

Over the last decade, the burden of malaria has fallen dramatically in the Greater Mekong Subregion, with deaths falling by 95% and cases by 76% between 2012 and 2019.The declining malaria burden in GMS has largely attributed by the deployment of interventions of malaria prevention tools such as long-lasting Insecticidal Nets (LLIN), and widespread availability of rapid diagnostic tests and artemisinin combination therapies. However, residual transmission still exists among high risk populations, particularly mobile and migrant populations who enter forests for work. New interventions targetting these high risk groups are needed if countries of the Greater Mekong Subregion are to achieve malaria elimination by 2030. The study will be conducted in malaria endemic areas of Lao PDR (Attapeu, Saravanh, Savannakhet and Khammouane Provinces) and Cambodia (Preah Vihear, Stung Treng and Ratanakiri Provinces) which have large forest going MMP populations. The aim of the study is to assess the effectiveness, acceptability, feasibility and cost-effectiveness of a personal protection package to reduce malaria transmission among mobile and migrant populations (MMPs) and the general population in their residing villages in Lao People's Democratic Republic (PDR) and Cambodia. The personal protection package comprises a long-lasting insecticidal hammock net (LLIHN), insect repellent (Icaridin), and a behavioural change communication (BCC) package tailored to mobile and migrant populations. The study design is a stepped-wedge cluster-randomized controlled trial with nested mixed methods study. The stepped-wedge cluster randomized trial will estimate the effectiveness of a personal protection package provided to forest-going MMPs (the intervention) delivered by village malaria volunteers at the site (village/worksite) level on reducing Plasmodium spp. infections. Whilst the personal protection package will be provided to mobile and migrant populations in each village in a step-wise manner, primary and secondary outcomes relating to malaria testing will be collected in all consenting individuals in the village who present for malaria rapid diagnostic tests, whether they are mobile and migrant people or not.

The open stepped-wedge cluster-randomised controlled trial, randomized at the volunteer level (i.e. the volunteer and the village / workplaces they service), will be implemented between July 2021 to June 2022. The personal protection package for MMPs will be implemented sequentially in a minimum of ~488 villages serviced by approximately ~488 VMWs (~428 in Lao PDR and ~60 in Cambodia). Villages from each country will be randomised into 11 ordered blocks, with blocks transitioned from control (no personal protection package) to intervention (distribution of personal protection package) states at monthly intervals (10 blocks of 44 villages for the first 10 steps and a block of 48 villages transitioned at the last step). This follows an initial baseline control period of one-month at the start of the study

Approximately 11 RDTs per month will be undertaken in each study site (village/ worksite). Given the design we estimate that the study has power to detect a relative minimum detectable difference of 34% (OR = 0.66) in odds of RDT-detectable malaria infection due to the intervention (assuming a village intraclass correlation [ICC]= 0.42; 5% significance; 90% power and 1% RDT malaria prevalence).

For the stepped-wedged cluster randomized trial, both descriptive and primary outcome trial analyses will be performed. Using Stata version 15, differences in prevalence of Plasmodium spp. infections will be estimated across intervention and control periods using generalized linear mixed modelling (e.g. logit link function and binomial distribution) with crossed random effects for village and time, and intervention state, time and seasonality estimated as independent fixed factors. Temporal and spatial trends of Plasmodium spp. infections will also be explored including analysis of the effectiveness of the intervention across the study period. We will also explore any village-specific heterogeneity in effect by specifying a random effect for the intervention. Generalised linear mixed modelling will be extended to include model terms for country (main and interaction effects), and these will used to assess the extent of country-specific heterogeneity in intervention effect. The same approach will be used to assess risk group-specific heterogeneity (MMP, forest-goer, villager) in intervention effect.