Greater Mekong Subregion (GMS) - Studies to examine magnitude and identify causes: study sites in Thailand and Viet Nam

Greater Mekong Subregion (GMS) - Studies to examine magnitude and identify causes: study sites in Thailand and Viet Nam

Overview

Why this project?

Nearly 120 million people are at risk of malaria in the Greater Mekong Subregion (GMS). This is approximately 37% of the population.

Recently, there has been an increase in drug-resistant malaria in Southeast Asia.

P. falciparum is becoming resistant

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The aim

This study investigated the magnitude and causes of ongoing malaria transmission in two geographical areas of the GMS in Thailand and Viet Nam, across three ecological niches, namely, villages, farms and forested areas.

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Village
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Farm
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Forrest

The research sites

Thailand study sites:
Suan Oi village, Pha Man village and Komonae village (Tha Song Yang District, Tak Province)

Viet Nam study sites:
Son Thai Commune
(Khanh Vinh District, Khanh Hoa Province)

Research Components

Epidemiological Component

Objective

To determine the species of infection and key risk factors for infection, blood surveys and risk factor analysis based on demographics were conducted.

Methodology

Passive case detection (PCD) in health facilities was completed to analyse clinical malaria incidence during the study period. An analysis of historical data to understand how transmission levels had changed over time was undertaken.

Cross-sectional prevalence surveys were conducted in Thailand in the three study villages at four time points during 2016, as part of a concurrent study by Mahidol University. In Viet Nam, these surveys took place in August 2016.

Knowledge, attitudes and practices (KAP) surveys were undertaken at household level among the target villages in September 2016 in Thailand, and in August 2016 in Viet Nam.

Key findings: Thailand

  • The incidence of malaria – or the total number of cases - was very low in 2016 compared to 2015.

  • Malaria prevalence – or the proportion of cases out of every 1000 people - was very low.

  • P. vivax was the dominant species of infection.

  • Locally transmitted malaria cases made up the majority of all cases.

  • Villages did not have universal LLIN coverage.

  • One third of adults staying overnight on the farm reported that they did not use a net the last time they stayed there.

  • Almost all of those who stayed overnight in the forest reported that they did not use a net.

  • Large variation in sleeping times meant that there was overlap with mosquito biting hours.

Key findings: Viet Nam

  • Malaria incidence – or total number of cases - was slightly higher in 2016 compared to 2015.

  • The prevalence of malaria – or the proportion of cases out of every 1000 people - was low.

  • P. falciparum was the dominant species of infection.

  • Universal LLIN coverage had not been achieved.

  • Usage of nets the previous night was very high, but the types of nets used were unknown.

  • Half of farm-goers either never or rarely used nets in the field or farm plot.

  • Most forest-goers did not regularly use nets in the forest.

Sociological Component

Objective

To find out more about villagers’ patterns of movement and their behavioural practices, interviews and focus group discussions with risk groups and direct observations were conducted. Risk groups – the forest-goers and mobile groups – were given GPS tracking devices to monitor their movements and identify likely transmission spots.

Methodology

In both countries, forest-goers and other mobile groups were tracked using GPS-enabled tracking devices. Direct observation of villager behaviour was conducted concurrent to the mosquito collection times in each study site village. In Thailand, a total of 72 households were sampled. In Viet Nam, the collection teams visited 35 households in July, 35 in October, and 40 in December. Observational data was then compared against mosquito collection data in order to identify the time points of exposure to potentially infective mosquito bites and the behaviours that could lead to exposure.

Key informant interviews and focus group discussions were conducted in September 2016 in Thailand and October 2016 in Viet Nam. Eight focus group discussions and seven in-depth interviews were undertaken in Thailand. Three focus group discussions and 28 key informant interviews were undertaken in Viet Nam.

Key findings: Thailand

  • The communities’ practised subsistence farming; men, women and whole families could stay in the fields overnight in farm huts, particularly during certain times of the year when the workload on the farms was high.

  • There was regular border crossing to and from Myanmar.

  • Although men and women foraged in the forest, only men stayed overnight there. Repellent was used, but not nets.

  • Nets were only used on the farms if the household had extra nets to take to the farm huts.

  • The nets that were distributed for free were not large enough to accommodate the traditional sleeping arrangements in these households.

  • People sought healthcare when they had a fever. If people got sick on their farms on the Myanmar side of the border, they would travel back to Thailand for treatment.

  • Community members perceived malaria as low risk; mosquitoes were seen as less of a nuisance than they were in the past.

Key findings: Viet Nam

  • Most community members split their time between farm huts and village homes.

  • When farm huts were farther away or treated as the main residence, it was more likely that the whole family could stay there overnight. Closer farms would allow people to complete shorter trips with fewer household members staying there at one time.

  • Not everyone used nets in the farm huts.

  • Although both men and women went to the forest, only men stayed overnight; they did not use nets.

  • People would rise very early in the morning in the village and farm huts; but in the farm huts people would usually go to sleep very early, at around 7:30pm, as there was no electricity. Sometimes people, particularly males, would stay up later drinking and socialising.

  • Farm huts are bamboo structures, which could often be very open.

  • Most people sought healthcare when they had a fever; however, communities simultaneously perceived malaria as a low risk.

Entomological Component

Objective

To determine the infectivity of mosquitoes; the abundance of mosquito species; mosquito feeding times; whether mosquitoes fed on humans or animals; and whether they fed indoors or outdoors, using field and laboratory studies.

Methodology

Mosquitos were caught by human landing catch in the village, farm hut and forest sites. The bait cow catch technique was also used in the villages. In Thailand, collections were conducted in the villages from June to November 2016, and in farm and forest sites from August to November 2016. In Viet Nam, mosquito collections were conducted at three time points in July, October and December.

Vector species identification was based on morphology. In Thailand, Plasmodium infection was determined using ELISA, an enzyme-linked test that detects and measures antibodies in the blood. In Viet Nam, quantitative polymerase chain reaction (qPCR), a laboratory technique, was used to determine Plasmodium infection.

Key findings: Thailand

  • The abundance and species of Anopheles mosquitoes varied between the villages, farm plots and forest sites.

  • A variety of primary and secondary vectors were all present in one village and in farm or forest areas.

  • Only one An. minimus was found malaria positive by ELISA outdoors of a forested hamlet in August during the 05:00-06:00 collection.

  • Vectors mostly fed outdoors (exophagic) and fed on animals (zoophagic).

  • Hourly biting profiles showed that a relatively high amount of biting occurred before people went to bed and after they had woken up in the morning.

  • Net use inside households was high, but much of the indoor biting risk occurred in the early evening before people were under nets.

  • Collections took place only during the wet season, so researchers were unable to gain a full picture of seasonal trends.

Key findings: Viet Nam

  • There was minimal evidence of exposure risk in the village.

  • Farm hut and forest sites where there were large numbers of the primary vector species had a much higher exposure risk.

  • A variety of primary and secondary vectors were all present from cow-baited collections in one village.

  • Vector species mostly bit in the evening, including a large percentage before people went to bed.

  • Low net use existed among people staying in farm huts. Farm huts are open or partially open structures; this meant that outdoor and indoor biting rates were very similar.

  • An association was found between temperature, relative humidity, and the number of anophelines caught by cow bait. It is likely that rainfall impacted the October collection period; however, rainfall figures were unavailable to allow analysis of whether this influenced the associative findings.

  • Three An. dirus were found malaria positive by ELISA inside and outside farm huts between 19:00 h and 04:00 h.

Meteorological Component

Methodology

Data about temperature, relative humidity and light intensity were collected at the same time that mosquitoes in each village site were collected. Rainfall estimates were also collected from national weather monitoring stations.

Research Sites

The research sites

In this study, ongoing malaria transmission was studied across different ecological settings, namely village, farm and forest. The communities selected were those that practise subsistence farming, have dual residence between villages and farm huts, or have a substantial population that travels into forested regions. Selection of study sites also took into account a number of other factors relevant to the research, including the coverage of long-lasting insecticidal nets (LLINs) and/or indoor residual spraying (IRS).

Thailand study sites

Suan Oi village, Pha Man village and Komonae village (Tha Song Yang District, Tak Province)

In Thailand, the neighbouring villages of Suan Oi, Komonae and Pha Man were selected. These villages are situated in western Thailand on the border with Myanmar, and experience a high level of population mobility across the Thailand-Myanmar border, which is believed to increase malaria risk. Tak Province has an abundance of forests, hills and streams, providing optimal conditions for Anopheles mosquito breeding. Despite a LLIN coverage of 82% (Bureau of Vector-borne Diseases, 2015), in 2014 Tak was the province with the highest malaria incidence in Thailand (19 per 1000 population). The villages selected had the highest caseload at village level.

Viet Nam study sites

Son Thai Commune (Khanh Vinh District, Khanh Hoa Province)

According to local authorities, universal LLIN coverage had been achieved in the commune, making it an ideal study site to investigate RMT. Khanh Hoa Province is mostly mountainous, and forests cover more than half of it. Khanh Vinh District had the highest incidence rate of malaria at district level, and Son Thai Commune (made up of two neighbouring villages, Giang Bien and Bo Lang) had one of the highest incidence rates at commune level. Within the commune, there is also a large community practising subsistence and slash-and-burn agriculture, also known as swidden agriculture.

Key Findings

Universal LLIN coverage has not been achieved 

Ongoing malaria transmission is the malaria transmission that remains after universal coverage of long-lasting insecticidal nets (LLINs) has been achieved. This study showed that universal coverage of LLINs has not been achieved in the study sites, and therefore not all of the malaria cases seen could be attributed to ongoing malaria transmission.

  • Not enough LLINs had been distributed to cover each family member, and the LLINs provided were not sized for family beds.

  • LLINs were unavailable in the village markets, and concerns existed about the impregnation of nets with insecticides.

  • Substandard net maintenance and treatment was prevalent, and villagers used damaged nets.

  • There was limited to no use of mosquito nets in farm and forest sites. This was because families did not have spare nets to take to their farm huts, nets were cumbersome to carry, or it was not possible to use nets in the farm and forest environments.

This study showed that universal coverage of LLINs has not been achieved in the study site.

Factors contributing to malaria transmission

This study also showed that even if every individual in the study site were to use an LLIN when asleep, malaria transmission could still occur. This was due to a number of reasons, most notably:

  • Mosquitoes fed before people went to bed in the evenings and after they woke up in the mornings.

  • Mosquitoes displayed preference for outdoor feeding (exophagy) and animal feeding (zoophily). By remaining outdoors and feeding on animals, mosquitoes escaped contact with IRS and LLINs.

  • Higher mosquito abundance existed in forested areas, which is also where LLINs were used less frequently or could not be used.

Research Uptake

Research uptake objectives

The research will be used to inform policy, to educate local populations, and to develop simple, cost-effective protocols and tools that can be used locally and more widely by partner agencies across different ecological and epidemiological settings.

Key audiences

The key audiences for this study are:

  • Programme managers (in government)
  • Partners
  • Industries looking into novel tools for personal protection against mosquitoes and/or malaria

Meetings have already been held with local government officials to discuss study findings.

International meetings attended

Presentations were given at the following international meetings:

“Residual malaria transmission dynamics varies across the Greater Mekong Subregion despite high coverage of LLINs” – by Jeffrey Hii, American Society Tropical Medicine & Hygiene Symposium; SESSION 168 - Why is Malaria Transmission Persisting in Some Contexts Despite High Coverage of Vector Control Tools, Such as LLINs and IRS? Results From Recent Studies Across Three WHO Regions, New Orleans, Nov 1, 2018

“Vector control at the cross-roads in Asia-Pacific Region: public health entomology and residual malaria transmission” – by Jeffrey Hii, First Malaria World Congress, Melbourne, 1 - 5 July 2018.

“How much Residual Transmission in Greater Mekong Subregion: Thailand & Viet Nam” – Jeffrey Hii, Asia-Pacific Malaria Elimination Network Vector Control Working Group/Mekong Outdoor Malaria Transmission Network 2018 Meeting, Bangkok, 3-5 September 2018

Publications and Other Resources

Video

The Prinicipal Investigator, Dr Jeffrey Hii, was interviewed at the workshop on Residual Malaria held in Iquitos, Peru in 2019. In this video, he describes the aim and key findings from his project.

Summary booklets

These booklets provide an overview of the projects aims, methods and key findings. It also includes some suggested recommendations for how to address ongoing malaria transmission in the local context. These documents are taregted toward decision makers and other authorities in malaria control in Southeast Asia. View the booklet for Thailand and Vietnam here and here.

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Publications

Hii J, Vythilingam I, Roca-Feltrer A (2018). Human and Simian Malaria in the Greater Mekong Subregion and Challenges for Elimination, Towards Malaria Elimination. Sylvie Manguin and Vas Dev, IntechOpen, DOI: 10.5772/intechopen.76901. https://www.intechopen.com/books/towards-malaria-elimination-a-leap-forward/human-and-simian-malaria-in-the-greater-mekong-subregion-and-challenges-for-elimination

Edwards HM, Siriwichai P, Kirabitiir K et al. (2019) Transmission risk beyond the village - Entomological and human factors contributing to residual malaria transmission in an area approaching malaria elimination on the Thailand-Myanmar border. Malaria Journal 18:221. https://malariajournal.biomedcentral.com/articles/10.1186/s12936-019-2852-5

Edwards HM, Chinh V, Le Duy B et al. (2019) Characterising residual malaria transmission in forested areas with low coverage of core vector control in central Viet Nam. Parasites Vectors 12, 454. https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-019-3695-1

Articles to be submitted

To be submitted to WHO/TDR-Supplement Journal

Review of Residual Malaria Transmission in the Greater Mekong Subregion: new challenges and approaches – by Jeffrey Hii, Hannah M Edwards, Ron P. Marchand and Sean Hewitt.

To be submitted to International Journal of Health Geographics

Creating outdoor/residual malaria risk maps using GPS data-loggers for tracking human movement and exposure to Anopheles vectors in forested areas of Thai-Myanmar border and central Viet Nam – by Irwin F Chavez, Hannah M. Edwards, Vu Duc Chinh, Bui Le Duy, Pham Vinh Thanh, Ngo Duc Thang, Patchara Siriwichai, Kirakorn Kirabitiir, Jetsumon Prachumsri, Jeffrey Hii

News

APMEN VCWG/MOMTN Meeting 2018

3 - 5 September 2018, Bangkok, Thailand 

From 3 – 5 September 2018, the APMEN Vector Control Working Group (VCWG)/Mekong Outdoor Malaria Transmission Network (MOMTN) was held in Bangkok, Thailand. The meeting was attended by 16 country members and 19 institutional partners from across the region, with the purpose of “Moving towards vector surveillance and response system for malaria elimination”.

The aims of the meeting were to:

  • Review and share information and experience of progress, good practice and studies for outdoor malaria transmission.
  • Discuss implications of outdoor transmission and country efforts for malaria elimination.

During the session on Residual Malaria, Dr Jeffrey Hii delivered a presentation titled, “How much residual transmission in GMS: Thailand and Viet Nam”. Dr Hii presented results from his mixed methods study which investigated the magnitude and factors contributing to low (<1% prevalence) but sustained malaria transmission in rural communities.

The study findings suggest that primary drivers of residual malaria transmission in the study sites were due to:

  • Higher mosquito abundance in forested areas where LLINs were used less frequently or could not be used;
  • Human-mosquito interaction in sites without LLIN/IRS and/or where LLIN could not be used;
  • Late sleeping and waking times coinciding with peak biting hours;
  • Feeding preferences of Anopheles mosquitos (e.g. feeding outdoors or on animals) taking them away from LLINs and IRS;
  • Non-use of LLIN or using torn/damaged LLINs;
  • High population movement across the border and into forested areas; and
  • Plasmodium vivax predominance resulting in relapse of previous infection.
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Photo of participants at the APMEN VCWG meeting (credit: https://www.apmen.org)

One of his recommendations was to explore personal protection methods that are appropriate within these local areas. He also suggested investigating the durability and ease of use of protection products, as well as those that require minimal behaviour change and communication. The study also highlighted the need for a more holistic definition of RMT, as net use is often overestimated and does not consider people outside of the household, or lower LLIN coverage in farm huts and forest areas.

The meeting led to several important and shared decisions, including an agreement among APMEN members to initiate a multi-country proof of concept study on vector control tools to address outdoor transmission. View more details about the objectives, expected outputs and the agenda of the meeting here.

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Collaborating Partners

Donors

This work is financially and technically supported by TDR, the Special Programme for Research and Training in Tropical Diseases. Technical support is also provided by the World Health Organization Global Malaria Programme. UK Aid also provides financial support.

Partners

  • Malaria Consortium
  • Mahidol Vivax Research Unit, Mahidol University, Thailand
  • National Institute Malariology, Parasitology and Entomology (NIMPE), Viet Nam
  • Queensland Institute Medical Research (QIMR) Berghofer, Medical Research Institute

Collaborators

  • Bureau of Vector-borne Diseases (VBDU), Thailand and VBDC, Tha Song Yang
  • Provincial, district and commune health departments in Khanh Hoa, Viet Nam

Contact Details

Contact

Principal Investigator: Dr Jeffrey Hii

Email: Jeffrey_Hii@pmivectorlink.com