Opinion
Novel Approaches to Control Malaria in Forested Areas of Southeast Asia

https://doi.org/10.1016/j.pt.2019.03.011Get rights and content

Highlights

Much progress has been made in the control of falciparum malaria in the GMS, but transmission persists in forested areas.

The programmatic use of chemoprevention for malaria control has been controversial in the past but is increasingly accepted. For example, seasonal malaria chemoprevention is successfully rolled out to prevent malaria in children living in the Sahel.

Forest workers are another population exposed to malaria transmission for limited periods who could benefit from antimalarial prophylaxis.

Research is ongoing to explore and optimize antimalarial regimens to protect forest workers against malaria.

The emergence and spread of drug resistance in the Greater Mekong Subregion (GMS) have added urgency to accelerate malaria elimination while reducing the treatment options. The remaining foci of malaria transmission are often in forests, where vectors tend to bite during daytime and outdoors, thus reducing the effectiveness of insecticide-treated bed nets. Limited periods of exposure suggest that chemoprophylaxis could be a promising strategy to protect forest workers against malaria. Here we discuss three major questions in optimizing malaria chemoprophylaxis for forest workers: which antimalarial drug regimens are most appropriate, how frequently the chemoprophylaxis should be delivered, and how to motivate forest workers to use, and adhere to, malaria prophylaxis.

Section snippets

Spreading Multidrug Resistance Adds Urgency to Elimination

Between 2000 and 2017 the malaria burden in the Greater Mekong Subregion (GMS; see Glossary) has decreased in a heterogeneous fashion (Figure 1). China succeeded in interrupting endogenous malaria transmission by 2017 [1]. Close monitoring, rapid case investigation, reporting, and response played critical roles in this success [2]. In Myanmar, the country with the highest malaria burden, the number of reported malaria cases dropped below 100 000 only in 2017. Two studies published in 2018

Concentration of Malaria Transmission in Forested Areas of the GMS

The importance of forests in malaria transmission in Indochina was well established in the 20th century [5]. With better malaria control in residential areas the relative importance of the still poorly controlled transmission of malaria in forested areas has increased. By 2019 malaria transmission is concentrated in the forested areas of Cambodia, Myanmar, Laos, and Vietnam. As shown in multiple studies, the population at highest risk for malaria in the GMS are adults who work in forested areas

Current Malaria Prevention Methods Used by Forest Workers

Forest workers use a range of malaria prevention strategies [22]. Wearing long-sleeved shirts, trousers and socks can reduce mosquito bites but can be unbearably hot in tropical forests 23, 24, 25. Forest workers rely on mosquitoes avoiding smoke by starting fires around their work and campsites 26, 27, 28. Smouldering mosquito coils releasing spatial repellents such as pyrethrins can kill or at least knock down mosquitoes and are worn by forest workers in a portable coil holder or attached to

Concluding Remarks

In the GMS, malaria is predominantly a disease in adults who become infected during outdoor work in forested areas. The currently available vector-control measures, including insecticide spraying and treated bed nets, have little effect on mosquitoes that preferentially bite outdoors and during daytime. To eliminate malaria from the GMS it is essential to stop malaria transmission in forested areas in addition to already ongoing malaria-elimination efforts. Antimalarial prophylaxis for forest

Acknowledgments

We are indebted to our colleagues who helped the development of this paper in many discussions over the years.

Glossary

Artemisinin combination therapy (ACT)
is the combination of an artemisinin derivative with a partner drug. The artemisinin component reduces the number of susceptible parasites during the first 3 days of treatment (reduction of parasite biomass), while the role of the partner drug is to eliminate the remaining parasites, including artemisinin-tolerant parasites. ACTs fail when both partner drugs no longer clear the parasites. The spread of parasites resistant to artemisinin derivatives and

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      In Cambodia, malaria incidence has reached very low levels, with fewer than 5000 cases reported in 2021, of which around 90% were caused by Plasmodium vivax and 10% by P falciparum.4 In much of the Greater Mekong subregion, including Cambodia, the remaining malaria transmission is concentrated in forested areas.5,6 Addressing the remaining parasite reservoir in forest goers is essential to reach the goal of malaria elimination within the proposed time frame.7

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