Choosing interventions to eliminate forest malaria: preliminary results of two operational research studies inside Cambodian forests

Amber Kunkel,Amélie Vantaux,Benoit Witkowski,Jean-Olivier Guintran,Phanith Kong,Sophea Iv,Sarun Im,Sreynet Srun,Patrice Piola,Saorin Kim,Mark Debackere,Nimol Khim,Jean Popovici,Dom Peov,Chea Nguon,Srean Chhim

doi:10.1186/s12936-020-03572-3

Abstract

BackgroundRapid elimination of Plasmodium falciparum malaria in Cambodia is a goal with both national and international significance. Transmission of malaria in Cambodia is limited to forest environments, and the main population at risk consists of forest-goers who rely on forest products for income or sustenance. The ideal interventions to eliminate malaria from this population are unknown.MethodsIn two forested regions of Cambodia, forest-goers were trained to become forest malaria workers (FMWs). In one region, FMWs performed mass screening and treatment, focal screening and treatment, and passive case detection inside the forest. In the other region, FMWs played an observational role for the first year, to inform the choice of intervention for the second year. In both forests, FMWs collected blood samples and questionnaire data from all forest-goers they encountered. Mosquito collections were performed in each forest.ResultsMalaria prevalence by PCR was high in the forest, with 2.3–5.0% positive for P. falciparum and 14.6–25.0% positive for Plasmodium vivax among forest-goers in each study site. In vectors, malaria prevalence ranged from 2.1% to 9.6%, but no P. falciparum was observed. Results showed poor performance of mass screening and treatment, with sensitivity of rapid diagnostic tests equal to 9.1% (95% CI 1.1%, 29.2%) for P. falciparum and 4.4% (95% CI 1.6%, 9.2%) for P. vivax. Malaria infections were observed in all demographics and throughout the studied forests, with no clear risk factors emerging.ConclusionsMalaria prevalence remains high among Cambodian forest-goers, but performance of rapid diagnostic tests is poor. More adapted strategies to this population, such as intermittent preventive treatment of forest goers, should be considered.

Highlights

Rapid elimination of Plasmodium falciparum malaria in Cambodia is a goal with both national and international significance
The proportion of forest goers in the observation-intervention study who reported logging declined between June and September, corresponding to a period of crackdowns on illegal logging throughout Cambodia (Additional file 1: Fig S1); enrollments in the mass screening and treatment (MSAT) study began during this crackdown period
Rapid diagnostic test (RDT) sensitivity is low inside the forest, and the risk appears fairly homogeneous across all categories of individuals in these high-risk locations

Summary

Introduction

Rapid elimination of Plasmodium falciparum malaria in Cambodia is a goal with both national and international significance. Until recently the primary malaria control strategies in Cambodia have almost all been implemented outside of forests, in either villages or health centers, which may not fully capture asymptomatic carriers from this this high-risk population. One approach towards malaria control inside forests is tailored vector control measures such as hammock nets, but these may be of limited utility depending on patterns of user behaviour [18,19,20]. Another idea that has been proposed is the implementation of chemoprophylaxis to forest goers [12]. A new system of mobile malaria workers, intended to screen (with rapid diagnostic tests, RDTs) and treat individuals both around and inside the forest fringe, has been recently implemented [21]

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