The practice of jhum cultivation and its relationship to Plasmodium falciparum infection in the Chittagong Hill Districts of Bangladesh

Mathematical models of Plasmodium vivax transmission: A scoping review

Plasmodium vivax is one of the most geographically widespread malaria parasites in the world, primarily found across South-East Asia, Latin America, and parts of Africa. One of the significant characteristics of the P. vivax parasite is its ability to remain dormant in the human liver as hypnozoites and subsequently reactivate after the initial infection (i.e. relapse infections). Mathematical modelling approaches have been widely applied to understand P. vivax dynamics and predict the impact of intervention outcomes. Models that capture P. vivax dynamics differ from those that capture P. falciparum dynamics, as they must account for relapses caused by the activation of hypnozoites. In this article, we provide a scoping review of mathematical models that capture P. vivax transmission dynamics published between January 1988 and May 2023. The primary objective of this work is to provide a comprehensive summary of the mathematical models and techniques used to model P. vivax dynamics. In doing so, we aim to assist researchers working on mathematical epidemiology, disease transmission, and other aspects of P. vivax malaria by highlighting best practices in currently published models and highlighting where further model development is required. We categorise P. vivax models according to whether a deterministic or agent-based approach was used. We provide an overview of the different strategies used to incorporate the parasite's biology, use of multiple scales (within-host and population-level), superinfection, immunity, and treatment interventions. In most of the published literature, the rationale for different modelling approaches was driven by the research question at hand. Some models focus on the parasites' complicated biology, while others incorporate simplified assumptions to avoid model complexity. Overall, the existing literature on mathematical models for P. vivax encompasses various aspects of the parasite's dynamics. We recommend that future research should focus on refining how key aspects of P. vivax dynamics are modelled, including spatial heterogeneity in exposure risk and heterogeneity in susceptibility to infection, the accumulation of hypnozoite variation, the interaction between P. falciparum and P. vivax, acquisition of immunity, and recovery under superinfection.

Bangladesh in the era of malaria elimination

Bangladesh has dramatically reduced malaria by 93% from 2008 to 2020. The strategy has been district-wise, phased elimination; however, the last districts targeted for elimination include remote, forested regions which present several challenges for prevention, detection, and treatment of malaria. These districts border Myanmar which harbors Plasmodium falciparum malaria parasites resistant to artemisinins, key drugs used in artemisinin-based combination therapies (ACTs) that have been vital for control programs. Challenges in monitoring emergence of artemisinin resistance (AR), tracking parasite reservoirs, changes in vector behavior and responses to insecticides, as well as other environmental and host factors (including the migration of Forcibly Displaced Myanmar Nationals; FDMNs) may pose added hazards in the final phase of eliminating malaria in Bangladesh.

Human behaviour directs household-level exposure to malaria vectors in Bandarban, Bangladesh

BACKGROUND

Bangladesh has reduced malaria incidence and mortality by over 75% between 2010 and 2020. Widespread long-lasting insecticidal net (LLIN) distribution and use is one of the measures responsible for this success. Recalcitrant malaria hotspots within the Chittagong Hill Tracts districts suggest important drivers of malaria risk may remain uncharacterized.

METHODS

Towards understanding how household-level human behaviour impacts exposure to mosquitoes, parallel human landing catches and human behavioural observations were conducted in four households for 6 months (May-October) over the rainy season in the Bandarban District. Analysis quantifies spatiotemporal human behaviour-adjusted exposure to Anopheles with and without LLINs.

RESULTS

This small-scale operational study demonstrates that human spatial and temporal presence along with LLIN use drives exposure to Anopheles. Though the four households had both outdoor and indoor exposure, especially in the evening (1800-2000 h) and early morning (0400-0500 h), data points to household-based heterogeneity in malaria exposure even with similar LLIN access.

CONCLUSION

Incorporating human behaviour into exposure estimates can be used to understand the efficacy and limitations of local vector control strategies and identify gaps in protection, as well as where present intervention strategies may be optimized.

Heterogeneity in prevalence of subclinical Plasmodium falciparum and Plasmodium vivax infections but no parasite genomic clustering in the Chittagong Hill Tracts, Bangladesh

BACKGROUND

Malaria remains endemic in Bangladesh, with the majority of cases occurring in forested, mountainous region in the Chittagong Hill Tracts (CHT). This area is home to Bengali and diverse groups of indigenous people (Pahari) residing largely in mono-ethnic villages.

METHODS

1002 individuals of the 9 most prominent Pahari and the Bengali population were randomly selected and screened by RDT and qPCR. Parasites were genotyped by msp2 and deep sequencing of 5 amplicons (ama1-D3, cpmp, cpp, csp, and msp7) for Plasmodium falciparum (n = 20), and by microsatellite (MS) typing of ten loci and amplicon sequencing of msp1 for Plasmodium vivax (n = 21). Population structure was analysed using STRUCTURE software. Identity-by-state (IBS) was calculated as a measure of parasite relatedness and used to generate relatedness networks.

RESULTS

The prevalence of P. falciparum and P. vivax infection was 0.7% by RDT (P. falciparum 6/1002; P. vivax 0/1002, mixed: 1/1002) and 4% by qPCR (P. falciparum 21/1002; P. vivax 16/1002, mixed: 5/1002). Infections were highly clustered, with 64% (27/42) of infections occurring in only two Pahari groups, the Khumi and Mro. Diversity was high; expected heterozygosity was 0.93 for P. falciparum and 0.81 for P. vivax. 85.7% (18/21) of P. vivax and 25% (5/20) of P. falciparum infections were polyclonal. No population structure was evident for either species, suggesting high transmission and gene flow among Pahari groups.

CONCLUSIONS

High subclinical infection prevalence and genetic diversity mirror ongoing transmission. Control activities should be specifically directed to Pahari groups at greatest risk.

Dry Post Wintertime Mass Surveillance Unearths a Huge Burden of P. vivax, and Mixed Infection with P. vivax P. falciparum, a Threat to Malaria Elimination, in Dhalai, Tripura, India

With India aiming to achieve malaria elimination by 2030, several strategies have been put in place. With that aim, mass surveillance is now being conducted in some malaria-endemic pockets. As dry season mass surveillance has been shown to have its importance in targeting the reservoir, a study was undertaken to assess the parasite load by a sensitive molecular method during one of the mass surveys conducted in the dry winter period. It was executed in two malaria-endemic villages of Dhalai District, Tripura, in northeast India, also reported as P. falciparum predominated area. The present study found an enormous burden of Rapid Diagnostic Test negative malaria cases with P. vivax along with P. vivax and P. falciparum mixed infections during the mass surveillance from febrile and afebrile cases in dry winter months (February 2021–March 2021). Of the total 150 samples tested, 72 (48%) were positive and 78 (52%) negative for malaria by PCR. Out of the 72 positives, 6 (8.33%) were P. falciparum, 40 (55.55%) P. vivax, and 26 (36.11%) mixed infections. Out of 78 malaria negative samples, 6 (7.7%) were with symptoms, while among the total malaria positive, 72 cases 7 (9.8%) were with symptoms, and 65 (90.2%) were asymptomatic. Out of 114 samples tested by both microscopy and PCR, 42 samples turned out to be submicroscopic with 4 P. falciparum, 23 P. vivax, and 15 mixed infections. Although all P. vivax submicroscopic infections were asymptomatic, three P. falciparum cases were found to be febrile. Evidence of malaria transmission was also found in the vectors in the winter month. The study ascertained the use of molecular diagnostic techniques in detecting the actual burden of malaria, especially of P. vivax, in mass surveys. As Jhum cultivators in Tripura are at high risk, screening for the malarial reservoirs in pre-Jhum months can help with malaria control and elimination.

Glucose-6-phosphate dehydrogenase activity in individuals with and without malaria: Analysis of clinical trial, cross-sectional and case-control data from Bangladesh

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) activity is dependent upon G6PD genotype and age of the red blood cell (RBC) population, with younger RBCs having higher activity. Peripheral parasitemia with Plasmodium spp. induces hemolysis, replacing older RBCs with younger cells with higher G6PD activity. This study aimed to assess whether G6PD activity varies between individuals with and without malaria or a history of malaria.

METHODS AND FINDINGS

Individuals living in the Chittagong Hill Tracts of Bangladesh were enrolled into 3 complementary studies: (i) a prospective, single-arm clinical efficacy trial of patients (n = 175) with uncomplicated malaria done between 2014 and 2015, (ii) a cross-sectional survey done between 2015 and 2016 (n = 999), and (iii) a matched case-control study of aparasitemic individuals with and without a history of malaria done in 2020 (n = 506). G6PD activity was compared between individuals with and without malaria diagnosed by microscopy, rapid diagnostic test (RDT), or polymerase chain reaction (PCR), and in aparasitemic participants with and without a history of malaria. In the cross-sectional survey and clinical trial, 15.5% (182/1,174) of participants had peripheral parasitemia detected by microscopy or RDT, 3.1% (36/1,174) were positive by PCR only, and 81.4% (956/1,174) were aparasitemic. Aparasitemic individuals had significantly lower G6PD activity (median 6.9 U/g Hb, IQR 5.2-8.6) than those with peripheral parasitemia detected by microscopy or RDT (7.9 U/g Hb, IQR 6.6-9.8, p < 0.001), but G6PD activity similar to those with parasitemia detected by PCR alone (submicroscopic parasitemia) (6.1 U/g Hb, IQR 4.8-8.6, p = 0.312). In total, 7.7% (14/182) of patients with malaria had G6PD activity < 70% compared to 25.0% (248/992) of participants with submicroscopic or no parasitemia (odds ratio [OR] 0.25, 95% CI 0.14-0.44, p < 0.001). In the case-control study, the median G6PD activity was 10.3 U/g Hb (IQR 8.8-12.2) in 253 patients with a history of malaria and 10.2 U/g Hb (IQR 8.7-11.8) in 253 individuals without a history of malaria (p = 0.323). The proportion of individuals with G6PD activity < 70% was 11.5% (29/253) in the cases and 15.4% (39/253) in the controls (OR 0.7, 95% CI 0.41-1.23, p = 0.192). Limitations of the study included the non-contemporaneous nature of the clinical trial and cross-sectional survey.

CONCLUSIONS

Patients with acute malaria had significantly higher G6PD activity than individuals without malaria, and this could not be accounted for by a protective effect of G6PD deficiency. G6PD-deficient patients with malaria may have higher than expected G6PD enzyme activity and an attenuated risk of primaquine-induced hemolysis compared to the risk when not infected.

Disparities in Risks of Malaria Associated with Climatic Variability among Women, Children and Elderly in the Chittagong Hill Tracts of Bangladesh

Malaria occurrence in the Chittagong Hill Tracts in Bangladesh varies by season and year, but this pattern is not well characterized. The role of environmental conditions on the occurrence of this vector-borne parasitic disease in the region is not fully understood. We extracted information on malaria patients recorded in the Upazila (sub-district) Health Complex patient registers of Rajasthali in Rangamati district of Bangladesh from February 2000 to November 2009. Weather data for the study area and period were obtained from the Bangladesh Meteorological Department. Non-linear and delayed effects of meteorological drivers, including temperature, relative humidity, and rainfall on the incidence of malaria, were investigated. We observed significant positive association between temperature and rainfall and malaria occurrence, revealing two peaks at 19 °C (logarithms of relative risks (logRR) = 4.3, 95% CI: 1.1-7.5) and 24.5 °C (logRR = 4.7, 95% CI: 1.8-7.6) for temperature and at 86 mm (logRR = 19.5, 95% CI: 11.7-27.3) and 284 mm (logRR = 17.6, 95% CI: 9.9-25.2) for rainfall. In sub-group analysis, women were at a much higher risk of developing malaria at increased temperatures. People over 50 years and children under 15 years were more susceptible to malaria at increased rainfall. The observed associations have policy implications. Further research is needed to expand these findings and direct resources to the vulnerable populations for malaria prevention and control in the Chittagong Hill Tracts of Bangladesh and the region with similar settings.

Precarity at the Margins of Malaria Control in the Chittagong Hill Tracts in Bangladesh: A Mixed-Methods Study

Bangladesh has achieved significant progress towards malaria elimination, although health service delivery for malaria remains challenging in remote forested areas such as the Chittagong Hill Tracts (CHT). The aim of this study was to investigate perceptions of malaria and its treatment among the local population to inform contextualized strategies for rolling out radical cure for P. vivax in Bangladesh. The study comprised two sequential strands whereby the preliminary results of a qualitative strand informed the development of a structured survey questionnaire used in the quantitative strand. Results show that ethnic minority populations in the CHT live in precarious socio-economic conditions which increase their exposure to infectious diseases, and that febrile patients often self-treat, including home remedies and pharmaceuticals, before attending a healthcare facility. Perceived low quality of care and lack of communication between Bengali health providers and ethnic minority patients also affects access to public healthcare. Malaria is viewed as a condition that affects vulnerable people weakened by agricultural work and taking away blood is perceived to increase such vulnerability. Healthcare providers that initiate and sustain a dialogue about these issues with ethnic minority patients may foster the trust that is needed for local malaria elimination efforts.

Mapping the travel patterns of people with malaria in Bangladesh

BACKGROUND

Spread of malaria and antimalarial resistance through human movement present major threats to current goals to eliminate the disease. Bordering the Greater Mekong Subregion, southeast Bangladesh is a potentially important route of spread to India and beyond, but information on travel patterns in this area are lacking.

METHODS

Using a standardised short survey tool, 2090 patients with malaria were interviewed at 57 study sites in 2015-2016 about their demographics and travel patterns in the preceding 2 months.

RESULTS

Most travel was in the south of the study region between Cox's Bazar district (coastal region) to forested areas in Bandarban (31% by days and 45% by nights), forming a source-sink route. Less than 1% of travel reported was between the north and south forested areas of the study area. Farmers (21%) and students (19%) were the top two occupations recorded, with 67 and 47% reporting travel to the forest respectively. Males aged 25-49 years accounted for 43% of cases visiting forests but only 24% of the study population. Children did not travel. Women, forest dwellers and farmers did not travel beyond union boundaries. Military personnel travelled the furthest especially to remote forested areas.

CONCLUSIONS

The approach demonstrated here provides a framework for identifying key traveller groups and their origins and destinations of travel in combination with knowledge of local epidemiology to inform malaria control and elimination efforts. Working with the NMEP, the findings were used to derive a set of policy recommendations to guide targeting of interventions for elimination.

Knowledge, attitudes, and practices regarding malaria control among the slash and burn cultivators in Rangamati Hill tracts of Bangladesh

Background

Slash and burn cultivators are a significant risk group for malaria in South-East Asia. As envisaged in the National Strategic Plan for Malaria Elimination, Bangladesh aims to achieve zero indigenous malaria transmission by 2030. For the national plan to move from malaria control to malaria elimination, targeting the population of slash and burn cultivators is of overriding importance.

Methods

The study used an explorative mixed method design to investigate the knowledge, attitudes, and practices (KAP) regarding malaria prevention and treatment in an endemic area of Bangladesh. Adult slash and burn cultivators in two sub-districts of the Rangamati District were selected and interviewed. Four focus group discussions were conducted, and this was followed by a cross-sectional quantitative survey with 200 participants.

Results

The respondents’ general knowledge about malaria transmission and modes of prevention and treatment was good. However, there were some gaps regarding knowledge about specific aspects of malaria transmission and in particular about the increased risk associated with their occupation. Despite a much-reduced incidence of malaria in the study area, the respondents perceived the disease as life-threatening and knew that it needs rapid attention from a health worker. Moreover, the specific services offered by the local community health workers for malaria diagnosis and treatment were highly appreciated. Finally, the use of insecticide-treated mosquito nets (ITN) was considered as important and this intervention was uniformly stated as the main malaria prevention method.

Conclusions

The findings from this study on promising KAP characteristics in the slash and burn cultivator population are reassuring that the goal of malaria elimination by the year 2030 can be achieved in Bangladesh.

Mapping the stability of malaria hotspots in Bangladesh from 2013 to 2016

BACKGROUND

Malaria claims hundreds of thousands of lives each year, most of them children. A "malaria-free world" is the World Health Organization's vision, but elimination from the southeast Asian Region is hampered by factors including anti-malarial resistance and systematic underreporting. Malaria is a significant public health problem in Bangladesh and while there have been recent gains in control, there is large spatial and temporal heterogeneity in the disease burden. This study aims to determine the pattern and stability of malaria hotspots in Bangladesh with the end goal of informing intervention planning for elimination.

RESULTS

Malaria in Bangladesh exhibited highly seasonal, hypoendemic transmission in geographic hotspots, which remained conserved over time. The southeast areas of the Chittagong Hill Tracts were identified as malaria hotspots for all 4 years examined. Similarly, areas in Sunamganj and Netrakona districts in the Northeast were hotspots for 2013-2016. Highly stable hotspots from 1 year predicted the following year's hotspot locations in the southeast of Bangladesh. Hotspots did not appear to act as sources of spread with no evidence of consistent patterns of contiguous spread or recession of hotspots as high or low transmission seasons progressed.

CONCLUSIONS

Areas were identified with temporal and spatial clustering of high malaria incidence in Bangladesh. Further studies are required to understand the vector, sociodemographic and disease dynamics within these hotspots. Given the low caseloads occurring in the low transmission seasons, and the conserved nature of malaria hotspots, directing resources towards these areas may be an efficient way to achieve malaria elimination in Bangladesh.

Subclinical Plasmodium falciparum infections act as year-round reservoir for malaria in the hypoendemic Chittagong Hill districts of Bangladesh

OBJECTIVES

An analysis of the risk factors and seasonal and spatial distribution of individuals with subclinical malaria in hypoendemic Bangladesh was performed.

METHODS

From 2009 to 2012, active malaria surveillance without regard to symptoms was conducted on a random sample (n=3971) and pregnant women (n=589) during a cohort malaria study in a population of 24000.

RESULTS

The overall subclinical Plasmodium falciparum malaria point prevalence was 1.0% (n=35), but was 3.2% (n=18) for pregnant women. The estimated incidence was 39.9 per 1000 person-years for the overall population. Unlike symptomatic malaria, with a marked seasonal pattern, subclinical infections did not show a seasonal increase during the rainy season. Sixty-nine percent of those with subclinical P. falciparum infections reported symptoms commonly associated with malaria compared to 18% without infection. Males, pregnant women, jhum cultivators, and those living closer to forests and at higher elevations had a higher prevalence of subclinical infection.

CONCLUSIONS

Hypoendemic subclinical malaria infections were associated with a number of household and demographic factors, similar to symptomatic cases. Unlike clinical symptomatic malaria, which is highly seasonal, these actively detected infections were present year-round, made up the vast majority of infections at any given time, and likely acted as reservoirs for continued transmission.

Targeting populations at higher risk for malaria: a survey of national malaria elimination programmes in the Asia Pacific

Background

Significant progress has been made in reducing the malaria burden in the Asia Pacific region, which is aggressively pursuing a 2030 regional elimination goal. Moving from malaria control to elimination requires National Malaria Control Programmes (NMCPs) to target interventions at populations at higher risk, who are often not reached by health services, highly mobile and difficult to test, treat, and track with routine measures, and if undiagnosed, can maintain parasite reservoirs and contribute to ongoing transmission.

Methods

A qualitative, free-text questionnaire was developed and disseminated among 17 of the 18 partner countries of the Asia Pacific Malaria Elimination Network (APMEN).

Results

All 14 countries that responded to the survey identified key populations at higher risk of malaria in their respective countries. Thirteen countries engage in the dissemination of malaria-related Information, Education, and Communication (IEC) materials. Eight countries engage in diagnostic screening, including of mobile and migrant workers, military staff, and/or overseas workers. Ten countries reported distributing or recommending the use of long-lasting insecticide-treated nets (LLINs) among populations at higher risk with fewer countries engaging in other prevention measures such as indoor residual spraying (IRS) (two countries), spatial repellents (four countries), chemoprophylaxis (five countries), and mass drug administration (MDA) (three countries). Though not specifically tailored to populations at higher risk, 11 countries reported using mass blood surveys as a surveillance tool and ten countries map case data. Most NMCPs lack a monitoring and evaluation structure.

Conclusion

Countries in the Asia Pacific have identified populations at higher risk and targeted interventions to these groups but there is limited information on the effectiveness of these interventions. Platforms like APMEN offer the opportunity for the sharing of protocols and lessons learned related to finding, targeting and successfully clearing malaria from populations at higher risk. The sharing of programme data across borders may further strengthen national and regional efforts to eliminate malaria. This exchange of real-life experience is invaluable to NMCPs when scarce scientific evidence on the topic exists to aid decision-making and can further support NMCPs to develop strategies that will deliver a malaria-free Asia Pacific by 2030.

Targeting populations at higher risk for malaria: a survey of national malaria elimination programmes in the Asia Pacific

BACKGROUND

Significant progress has been made in reducing the malaria burden in the Asia Pacific region, which is aggressively pursuing a 2030 regional elimination goal. Moving from malaria control to elimination requires National Malaria Control Programmes (NMCPs) to target interventions at populations at higher risk, who are often not reached by health services, highly mobile and difficult to test, treat, and track with routine measures, and if undiagnosed, can maintain parasite reservoirs and contribute to ongoing transmission.

METHODS

A qualitative, free-text questionnaire was developed and disseminated among 17 of the 18 partner countries of the Asia Pacific Malaria Elimination Network (APMEN).

RESULTS

All 14 countries that responded to the survey identified key populations at higher risk of malaria in their respective countries. Thirteen countries engage in the dissemination of malaria-related Information, Education, and Communication (IEC) materials. Eight countries engage in diagnostic screening, including of mobile and migrant workers, military staff, and/or overseas workers. Ten countries reported distributing or recommending the use of long-lasting insecticide-treated nets (LLINs) among populations at higher risk with fewer countries engaging in other prevention measures such as indoor residual spraying (IRS) (two countries), spatial repellents (four countries), chemoprophylaxis (five countries), and mass drug administration (MDA) (three countries). Though not specifically tailored to populations at higher risk, 11 countries reported using mass blood surveys as a surveillance tool and ten countries map case data. Most NMCPs lack a monitoring and evaluation structure.

CONCLUSION

Countries in the Asia Pacific have identified populations at higher risk and targeted interventions to these groups but there is limited information on the effectiveness of these interventions. Platforms like APMEN offer the opportunity for the sharing of protocols and lessons learned related to finding, targeting and successfully clearing malaria from populations at higher risk. The sharing of programme data across borders may further strengthen national and regional efforts to eliminate malaria. This exchange of real-life experience is invaluable to NMCPs when scarce scientific evidence on the topic exists to aid decision-making and can further support NMCPs to develop strategies that will deliver a malaria-free Asia Pacific by 2030.