Progress in mosquito net coverage in Papua New Guinea

Genetic differentiation and bottleneck effects in the malaria vectors Anopheles farauti and Anopheles punctulatus after an LLIN-based vector control program in Papua New Guinea

Implementation of long-lasting insecticide-treated net (LLIN) programs to control human malaria transmission leads to substantial reductions in the abundance of Anopheles mosquitoes, but the impact on the population genetic structure of the malaria vectors is poorly known, nor has it been investigated in Papua New Guinea, where malaria is highly endemic and where several species of Anopheles have vector roles. Here, we applied Wright's F-statistic, analysis of molecular variance, Bayesian structure analysis, and discriminant analysis of principle components to microsatellite genotype data to analyze the population genetic structure of Anopheles farauti between and within the northern and southern lowland plains and of Anopheles punctulatus within the northern plain of Papua New Guinea after such a program. Bottleneck effects in the two malaria vectors were analyzed using Luikart and Cornuet's tests of heterozygosity. A large, panmictic population of An. punctulatus pre-LLIN program diverged into two subregional populations corresponding to Madang and East Sepik provinces post-LLIN distribution and experienced a genetic bottleneck during this process. By contrast, the An. farauti population existed as two regional populations isolated by mountain ranges pre-LLIN, a genetic structure that persisted after the distribution of LLINs with no further geographic differentiation nor evidence of a genetic bottleneck. These findings show the differential response of populations of different vector species to interventions, which has implications for program sustainability and gene flow.

Insecticide resistance in malaria and arbovirus vectors in Papua New Guinea, 2017-2022

BACKGROUND

Insecticide resistance (IR) monitoring is essential for evidence-based control of mosquito-borne diseases. While widespread pyrethroid resistance in Anopheles and Aedes species has been described in many countries, data for Papua New Guinea (PNG) are limited. Available data indicate that the local Anopheles populations in PNG remain pyrethroid-susceptible, making regular IR monitoring even more important. In addition, Aedes aegypti pyrethroid resistance has been described in PNG. Here, Anopheles and Aedes IR monitoring data generated from across PNG between 2017 and 2022 are presented.

METHODS

Mosquito larvae were collected in larval habitat surveys and through ovitraps. Mosquitoes were reared to adults and tested using standard WHO susceptibility bioassays. DNA from a subset of Aedes mosquitoes was sequenced to analyse the voltage-sensitive sodium channel (Vssc) region for any resistance-related mutations.

RESULTS

Approximately 20,000 adult female mosquitoes from nine PNG provinces were tested. Anopheles punctulatus sensu lato mosquitoes were susceptible to pyrethroids but there were signs of reduced mortality in some areas. Some Anopheles populations were also resistant to DDT. Tests also showed that Aedes. aegypti in PNG are resistant to pyrethroids and DDT and that there was also likelihood of bendiocarb resistance. A range of Vssc resistance mutations were identified. Aedes albopictus were DDT resistant and were likely developing pyrethroid resistance, given a low frequency of Vssc mutations was observed.

CONCLUSIONS

Aedes aegypti is highly pyrethroid resistant and also shows signs of resistance against carbamates in PNG. Anopheles punctulatus s.l. and Ae. albopictus populations exhibit low levels of resistance against pyrethroids and DDT in some areas. Pyrethroid-only bed nets are currently the only programmatic vector control tool used in PNG. It is important to continue to monitor IR in PNG and develop proactive insecticide resistance management strategies in primary disease vectors to retain pyrethroid susceptibility especially in the malaria vectors for as long as possible.

A review of malaria epidemiology and control in Papua New Guinea 1900 to 2021: Progress made and future directions

The research and control of malaria has a long history in Papua New Guinea, sometimes resulting in substantial changes to the distribution of infection and transmission dynamics in the country. There have been four major periods of malaria control in PNG, with the current control programme having commenced in 2004. Each previous control programme was successful in reducing malaria burden in the country, but multiple factors led to programme failures and eventual breakdown. A comprehensive review of the literature dating from 1900 to 2021 was undertaken to summarize control strategies, epidemiology, vector ecology and environmental drivers of malaria transmission in PNG. Evaluations of historical control programs reveal poor planning and communication, and difficulty in sustaining financial investment once malaria burden had decreased as common themes in the breakdown of previous programs. Success of current and future malaria control programs in PNG is contingent on adequate planning and management of control programs, effective communication and engagement with at-risk populations, and cohesive targeted approaches to sub-national and national control and elimination.

Asia-Pacific International Center of Excellence in Malaria Research: Maximizing Impact on Malaria Control Policy and Public Health in Cambodia and Papua New Guinea

The Asia-Pacific International Center of Excellence in Malaria Research (ICEMR) was funded in 2016 to conduct a coordinated set of field and in-depth biological studies in Cambodia and Papua New Guinea (PNG), in sites that span the range of transmission intensities currently found in the Asia-Pacific regions. The overall objective is to gain an understanding of key parasite, human host, and vector factors involved in maintaining transmission in the face of intensified control and elimination programs, and to develop novel approaches to identify and target residual transmission foci. In this article, we will describe how the ICEMR program was designed to address key knowledge gaps and priority areas for the malaria control programs in each country. In PNG, partners have worked together on two consecutive ICEMR grants (2009-2016 and 2017-2024) and we present a case study of the partnership and engagement approach that has led to stronger coordination of research activities and integration with program, informing country-level strategic planning and prioritization of control activities. In both settings, the ICEMR program has generated insights into transmission foci, risk factors for ongoing transmission, highlighting the hidden burden of vivax malaria, and the need for additional complementary vector control tools. Finally, we will summarize the emerging research questions and priority areas-namely surveillance, vivax malaria, new vector control tools, and community/health systems-oriented approaches-where further tool development and implementation research have been identified as being needed to guide policy.

Vector composition, abundance, biting patterns and malaria transmission intensity in Madang, Papua New Guinea: assessment after 7 years of an LLIN-based malaria control programme

Background

A malaria control programme based on distribution of long-lasting insecticidal bed nets (LLINs) and artemisinin combination therapy began in Papua New Guinea in 2009. After implementation of the programme, substantial reductions in vector abundance and malaria transmission intensity occurred. The research reported here investigated whether these reductions remained after seven years of sustained effort.

Methods

All-night (18:00 to 06:00) mosquito collections were conducted using human landing catches and barrier screen methods in four villages of Madang Province between September 2016 and March 2017. Anopheles species identification and sporozoite infection with Plasmodium vivax and Plasmodium falciparum were determined with molecular methods. Vector composition was expressed as the relative proportion of different species in villages, and vector abundance was quantified as the number of mosquitoes per barrier screen-night and per person-night. Transmission intensity was quantified as the number of sporozoite-infective vector bites per person-night.

Results

Five Anopheles species were present, but vector composition varied greatly among villages. Anopheles koliensis, a strongly anthropophilic species was the most prevalent in Bulal, Matukar and Wasab villages, constituting 63.7–73.8% of all Anopheles, but in Megiar Anopheles farauti was the most prevalent species (97.6%). Vector abundance varied among villages (ranging from 2.8 to 72.3 Anopheles per screen-night and 2.2–31.1 Anopheles per person-night), and spatially within villages. Malaria transmission intensity varied among the villages, with values ranging from 0.03 to 0.5 infective Anopheles bites per person-night. Most (54.1–75.1%) of the Anopheles bites occurred outdoors, with a substantial proportion (25.5–50.8%) occurring before 22:00.

Conclusion

The estimates of vector abundance and transmission intensity in the current study were comparable to or higher than estimates in the same villages in 2010–2012, indicating impeded programme effectiveness. Outdoor and early biting behaviours of vectors are some of the likely explanatory factors. Heterogeneity in vector composition, abundance and distribution among and within villages challenge malaria control programmes and must be considered when planning them.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-04030-4.

Nonrandom Selection and Multiple Blood Feeding of Human Hosts by Anopheles Vectors: Implications for Malaria Transmission in Papua New Guinea

Nonrandom selection and multiple blood feeding of human hosts by Anopheles mosquitoes may exacerbate malaria transmission. Both patterns of blood feeding and their relationship to malaria epidemiology were investigated in Anopheles vectors in Papua New Guinea (PNG). Blood samples from humans and mosquito blood meals were collected in villages and human genetic profiles ("fingerprints") were analyzed by genotyping 23 microsatellites and a sex-specific marker. Frequency of blood meals acquired from different humans, identified by unique genetic profiles, was fitted to Poisson and negative binomial distributions to test for nonrandom patterns of host selection. Blood meals with more than one genetic profiles were classified as mosquitoes that fed on multiple humans. The age of a person bitten by a mosquito was determined by matching the blood-meal genetic profile to the villagers' genetic profiles. Malaria infection in humans was determined by PCR test of blood samples. The results show nonrandom distribution of blood feeding among humans, with biased selection toward males and individuals aged 15-30 years. Prevalence of Plasmodium falciparum infection was higher in this age group, suggesting males in this age range could be super-spreaders of malaria parasites. The proportion of mosquitoes that fed on multiple humans ranged from 6% to 13% among villages. The patterns of host utilization observed here can amplify transmission and contribute to the persistence of malaria in PNG despite efforts to suppress it with insecticidal bed nets. Excessive feeding on males aged 15-30 years underscores the importance of targeted interventions focusing on this demographic group.

Examining the incentives and disincentives in the maintenance of Insecticide-Treated Nets among householders in Ghana

OBJECTIVE

This study explored the factors that affect the incentive to care for Insecticide-Treated Nets (ITNs) among householders in the Shai-Osudoku District of Ghana.

METHODS

The study employed a descriptive qualitative design. Four in-depth interviews (IDIs) and four focus group discussions (FGDs) were conducted to gather the data from 38 participants. A thematic technique was used to analyse the data.

FINDINGS

Householders were aware of the importance and use of ITNs. The factors underlying the motivation of householders to care for ITNs included their need to stay healthy; inadequate funds to acquire new ITNs and pay for healthcare cost; and their knowledge of the use and efficacy of ITNs. It was also found that obtaining the nets at no cost; limited time available to mend the ITNs; and limited knowledge on how to mend the ITNs disincentivised householders from effectively caring for the nets.

CONCLUSIONS

There is a need to rethink current ITN intervention programmes in ways that will improve the contents of public education messages and strengthen monitoring frameworks to ensure that householders take optimum care of their nets.

Coverage, determinants of use and repurposing of long-lasting insecticidal nets two years after a mass distribution in Lihir Islands, Papua New Guinea: a cross-sectional study

BACKGROUND

Universal coverage with long-lasting insecticidal nets (LLINs) is an essential component of malaria control programmes. Three-yearly mass distribution of LLINs in Papua New Guinea (PNG) has been successful in reducing infection transmission since 2009, but malaria prevalence ramped up from 2015 onwards. Although LLIN universal coverage is mostly achieved during these campaigns, it may not be related with net use over time. Uses given to LLINs and non-compliance of this strategy were evaluated.

METHODS

A knowledge, attitude and practice (KAP) cross-sectional study was conducted in Lihir Islands, PNG, 2-2.5 years after the last LLIN mass distribution campaign. Data on bed net ownership, use and maintenance behaviour was collected using a household questionnaire administered by trained community volunteers. Logistic regression models were used to identify factors associated with owning at least one LLIN and sleeping under a LLIN the previous night.

RESULTS

Among 2694 households surveyed, 27.4 % (95 % CI: 25.8-29.2) owned at least one LLIN and 8.7 % (95 % CI: 7.6-9.8) had an adequate LLIN coverage (at least one LLIN for every two people). Out of 13,595 individuals in the surveyed households, 13.6 % (95 % CI: 13.0--4.2) reported having slept under a LLIN the preceding night. Determinants for sleeping under LLIN included living in a household with adequate LLIN coverage [adjusted OR (aOR) = 5.82 (95 % CI: 3.23-10.49)], household heads knowledge about LLINs [aOR = 16.44 (95 % CI: 8.29-32.58)], and female gender [aOR = 1.92 (95 % CI: 1.53-2.40)] (all p-values < 0.001). LLIN use decreased with older age [aOR = 0.29 (95 % CI: 0.21-0.40) for ≥ 15 year-olds, aOR = 0.38 (95 % CI: 0.27-0.55) for 5-14 year-olds] compared to < 5 year-olds (p-value < 0.001). Knowledge on the use of LLIN was good in 37.0 % of the household heads. Repurposed nets were reported serving as fishing nets (30.4 %), fruits and seedlings protection (26.6 %), covering up food (19.0 %) and bed linen (11.5 %).

CONCLUSIONS

Two years after mass distribution, LLIN coverage and use in Lihir Islands is extremely low. Three yearly distribution campaigns may not suffice to maintain an acceptable LLIN coverage unless knowledge on maintenance and use is promoted trough educational campaigns.

Spatial prediction of malaria prevalence in Papua New Guinea: a comparison of Bayesian decision network and multivariate regression modelling approaches for improved accuracy in prevalence prediction

Background

Considerable progress towards controlling malaria has been made in Papua New Guinea through the national malaria control programme’s free distribution of long-lasting insecticidal nets, improved diagnosis with rapid diagnostic tests and improved access to artemisinin combination therapy. Predictive prevalence maps can help to inform targeted interventions and monitor changes in malaria epidemiology over time as control efforts continue. This study aims to compare the predictive performance of prevalence maps generated using Bayesian decision network (BDN) models and multilevel logistic regression models (a type of generalized linear model, GLM) in terms of malaria spatial risk prediction accuracy.

Methods

Multilevel logistic regression models and BDN models were developed using 2010/2011 malaria prevalence survey data collected from 77 randomly selected villages to determine associations of Plasmodium falciparum and Plasmodium vivax prevalence with precipitation, temperature, elevation, slope (terrain aspect), enhanced vegetation index and distance to the coast. Predictive performance of multilevel logistic regression and BDN models were compared by cross-validation methods.

Results

Prevalence of P. falciparum, based on results obtained from GLMs was significantly associated with precipitation during the 3 driest months of the year, June to August (β = 0.015; 95% CI = 0.01–0.03), whereas P. vivax infection was associated with elevation (β = − 0.26; 95% CI = − 0.38 to − 3.04), precipitation during the 3 driest months of the year (β = 0.01; 95% CI = − 0.01–0.02) and slope (β = 0.12; 95% CI = 0.05–0.19). Compared with GLM model performance, BDNs showed improved accuracy in prediction of the prevalence of P. falciparum (AUC = 0.49 versus 0.75, respectively) and P. vivax (AUC = 0.56 versus 0.74, respectively) on cross-validation.

Conclusions

BDNs provide a more flexible modelling framework than GLMs and may have a better predictive performance when developing malaria prevalence maps due to the multiple interacting factors that drive malaria prevalence in different geographical areas. When developing malaria prevalence maps, BDNs may be particularly useful in predicting prevalence where spatial variation in climate and environmental drivers of malaria transmission exists, as is the case in Papua New Guinea.

Residual Malaria Transmission in Select Countries of Asia-Pacific Region: Old Wine in a New Barrel

Background

Despite substantial reductions in malaria burden and improvement in case management, malaria remains a major public health challenge in the Asia-Pacific region. Residual malaria transmission (RMT) is the fraction of total transmission that persists after achievement of full operational coverage with effective insecticide-treated bed nets (ITNs)/long-lasting insecticidal nets (LLINs) and/or indoor residual spray interventions. There is a critical need to standardize and share best practices for entomological, anthropological, and product development investigative protocols to meet the challenges of RMT and elimination goals.

Methods

A systematic review was conducted to describe when and where RMT is occurring, while specifically targeting ownership and usage of ITN/LLINs, indoor residual spray application, insecticide susceptibility of vectors, and human and vector biting behavior, with a focus on nighttime activities.

Results

Sixty-six publications from 1995 to present met the inclusion criteria for closer review. Associations between local vector control coverage and use with behaviors of human and mosquito vectors varied by locality and circumstance. Consequently, the magnitude of RMT is insufficiently studied and analyzed with sparse estimates of individual exposure in communities, insufficient or incomplete observations of ITN/LLIN use, and the local human population movement into and from high-risk areas.

Conclusions

This review identified significant gaps or deficiencies that require urgent attention, namely, developing standardized procedures and methods to estimate risk exposure beyond the peridomestic setting, analytical approaches to measure key human-vector interactions, and seasonal location-specific agricultural or forest use calendars, and establishing the collection of longitudinal human and vector data close in time and location.

Human Behavior, Livelihood, and Malaria Transmission in Two Sites of Papua New Guinea

Background

Malaria transmission is currently resurging in Papua New Guinea (PNG). In addition to intervention coverage, social and cultural factors influence changes in epidemiology of malaria in PNG. This study aimed to better understand the role of human behavior in relation to current malaria control efforts.

Methods

A mixed-method design was used in 2 sites in PNG. In-depth interviews, focus group discussions, cross-sectional malaria indicator survey, and population census were implemented.

Results

We identified 7 population groups based on demographics and behavioral patterns with potential relevance to Anopheles exposure. People spend a substantial amount of time outdoors or in semiopen structures. Between 4 pm and 8 am, all types of activities across all groups in both study sites may be exposing individuals to mosquito bites; sleeping under a long-lasting insecticidal net was the exception. The later in the night, the more outdoor presence was concentrated in adult men.

Conclusions

Our findings highlight the potential of outdoor exposure to hamper malaria control as people spend a remarkable amount of time outdoors without protection from mosquitoes. To prevent ongoing transmission, targeting of groups, places, and activities with complementary interventions should consider setting-specific human behaviors in addition to epidemiological and entomological data.

Coverage outcomes (effects), costs, cost-effectiveness, and equity of two combinations of long-lasting insecticidal net (LLIN) distribution channels in Kenya: a two-arm study under operational conditions

BACKGROUND

Malaria-endemic countries distribute long-lasting insecticidal nets (LLINs) through combined channels with ambitious, universal coverage (UC) targets. Kenya has used eight channels with variable results. To inform national decision-makers, this two-arm study compares coverage (effects), costs, cost-effectiveness, and equity of two combinations of LLIN distribution channels in Kenya.

METHODS

Two combinations of five delivery channels were compared as 'intervention' and 'control' arms. The intervention arm comprised four channels: community health volunteer (CHV), antenatal and child health clinics (ANCC), social marketing (SM) and commercial outlets (CO). The control arm consisted of the intervention arm channels except mass campaign (MC) replaced CHV. Primary analysis used random sample household survey data, service-provider costs, and voucher or LLIN distribution data to compare between-arm effects, costs, cost-effectiveness, and equity. Secondary analyses compared costs and equity by channel.

RESULTS

The multiple distribution channels used in both arms of the study achieved high LLIN ownership and use. The intervention arm had significantly lower reported LLIN use the night before the survey (84·8% [95% CI 83·0-86·4%] versus 89·2% [95% CI 87·8-90·5%], p < 0·0001), higher unit costs ($10·56 versus $7·17), was less cost-effective ($86·44, 95% range $75·77-$102·77 versus $69·20, 95% range $63·66-$77·23) and more inequitable (Concentration index [C.Ind] = 0·076 [95% CI 0·057 to 0·095 versus C.Ind = 0.049 [95% CI 0·030 to 0·067]) than the control arm. Unit cost per LLIN distributed was lowest for MC ($3·10) followed by CHV ($10·81) with both channels being moderately inequitable in favour of least-poor households.

CONCLUSION

In line with best practices, the multiple distribution channel model achieved high LLIN ownership and use in this Kenyan study setting. The control-arm combination, which included MC, was the most cost-effective way to increase UC at household level. Mass campaigns, combined with continuous distribution channels, are an effective and cost-effective way to achieve UC in Kenya. The findings are relevant to other countries and donors seeking to optimise LLIN distribution.

TRIAL REGISTRATION

The assignment of the intervention was not at the discretion of the investigators; therefore, this study did not require registration.

Monitoring Plasmodium falciparum and Plasmodium vivax using microsatellite markers indicates limited changes in population structure after substantial transmission decline in Papua New Guinea

Monitoring the genetic structure of pathogen populations may be an economical and sensitive approach to quantify the impact of control on transmission dynamics, highlighting the need for a better understanding of changes in population genetic parameters as transmission declines. Here we describe the first population genetic analysis of two major human malaria parasites, Plasmodium falciparum (Pf) and Plasmodium vivax (Pv), following nationwide distribution of long-lasting insecticide-treated nets (LLINs) in Papua New Guinea (PNG). Parasite isolates from pre- (2005-2006) and post-LLIN (2010-2014) were genotyped using microsatellite markers. Despite parasite prevalence declining substantially (East Sepik Province: Pf = 54.9%-8.5%, Pv = 35.7%-5.6%, Madang Province: Pf = 38.0%-9.0%, Pv: 31.8%-19.7%), genetically diverse and intermixing parasite populations remained. Pf diversity declined modestly post-LLIN relative to pre-LLIN (East Sepik: R_s  = 7.1-6.4, H_E  = 0.77-0.71; Madang: R_s  = 8.2-6.1, H_E  = 0.79-0.71). Unexpectedly, population structure present in pre-LLIN populations was lost post-LLIN, suggesting that more frequent human movement between provinces may have contributed to higher gene flow. Pv prevalence initially declined but increased again in one province, yet diversity remained high throughout the study period (East Sepik: R_s  = 11.4-9.3, H_E  = 0.83-0.80; Madang: R_s  = 12.2-14.5, H_E  = 0.85-0.88). Although genetic differentiation values increased between provinces over time, no significant population structure was observed at any time point. For both species, a decline in multiple infections and increasing clonal transmission and significant multilocus linkage disequilibrium post-LLIN were positive indicators of impact on the parasite population using microsatellite markers. These parameters may be useful adjuncts to traditional epidemiological tools in the early stages of transmission reduction.

The epidemiology of Plasmodium falciparum and Plasmodium vivax in East Sepik Province, Papua New Guinea, pre- and post-implementation of national malaria control efforts

Background

In the past decade, national malaria control efforts in Papua New Guinea (PNG) have received renewed support, facilitating nationwide distribution of free long-lasting insecticidal nets (LLINs), as well as improvements in access to parasite-confirmed diagnosis and effective artemisinin-combination therapy in 2011–2012.

Methods

To study the effects of these intensified control efforts on the epidemiology and transmission of Plasmodium falciparum and Plasmodium vivax infections and investigate risk factors at the individual and household level, two cross-sectional surveys were conducted in the East Sepik Province of PNG; one in 2005, before the scale-up of national campaigns and one in late 2012-early 2013, after 2 rounds of LLIN distribution (2008 and 2011–2012). Differences between studies were investigated using Chi square (χ²), Fischer’s exact tests and Student’s t-test. Multivariable logistic regression models were built to investigate factors associated with infection at the individual and household level.

Results

The prevalence of P. falciparum and P. vivax in surveyed communities decreased from 55% (2005) to 9% (2013) and 36% to 6%, respectively. The mean multiplicity of infection (MOI) decreased from 1.8 to 1.6 for P. falciparum (p = 0.08) and from 2.2 to 1.4 for P. vivax (p < 0.001). Alongside these reductions, a shift towards a more uniform distribution of infections and illness across age groups was observed but there was greater heterogeneity across the study area and within the study villages. Microscopy positive infections and clinical cases in the household were associated with high rate infection households (> 50% of household members with Plasmodium infection).

Conclusion

After the scale-up of malaria control interventions in PNG between 2008 and 2012, there was a substantial reduction in P. falciparum and P. vivax infection rates in the studies villages in East Sepik Province. Understanding the extent of local heterogeneity in malaria transmission and the driving factors is critical to identify and implement targeted control strategies to ensure the ongoing success of malaria control in PNG and inform the development of tools required to achieve elimination. In household-based interventions, diagnostics with a sensitivity similar to (expert) microscopy could be used to identify and target high rate households.

Differential impact of malaria control interventions on P. falciparum and P. vivax infections in young Papua New Guinean children

INTRODUCTION

As malaria transmission declines, understanding the differential impact of intensified control on Plasmodium falciparum relative to Plasmodium vivax and identifying key drivers of ongoing transmission is essential to guide future interventions.

METHODS

Three longitudinal child cohorts were conducted in Papua New Guinea before (2006/2007), during (2008) and after scale-up of control interventions (2013). In each cohort, children aged 1-5 years were actively monitored for infection and illness. Incidence of malaria episodes, molecular force of blood-stage infections (_molFOB) and population-averaged prevalence of infections were compared across the cohorts to investigate the impact of intensified control in young children and the key risk factors for malaria infection and illness in 2013.

RESULTS

Between 2006 and 2008, P. falciparum infection prevalence, _molFOB, and clinical malaria episodes reduced by 47%, 59% and 69%, respectively, and a further 49%, 29% and 75% from 2008 to 2013 (prevalence 41.6% to 22.1% to 11.2%; _molFOB: 3.4 to 1.4 to 1.0 clones/child/year; clinical episodes incidence rate (IR) 2.6 to 0.8 to IR 0.2 episodes/child/year). P. vivax clinical episodes declined at rates comparable to P. falciparum between 2006, 2008 and 2013 (IR 2.5 to 1.1 to 0.2), while P. vivax _molFOB (2006, 9.8; 2008, 12.1) and prevalence (2006, 59.6%; 2008, 65.0%) remained high in 2008. However, in 2013, P. vivax _molFOB (1.2) and prevalence (19.7%) had also substantially declined. In 2013, 89% of P. falciparum and 93% of P. vivax infections were asymptomatic, 62% and 47%, respectively, were sub-microscopic. Area of residence was the major determinant of malaria infection and illness.

CONCLUSION

Intensified vector control and routine case management had a differential impact on rates of P. falciparum and P. vivax infections but not clinical malaria episodes in young children. This suggests comparable reductions in new mosquito-derived infections but a delayed impact on P. vivax relapsing infections due to a previously acquired reservoir of hypnozoites. This demonstrates the need to strengthen implementation of P. vivax radical cure to maximise impact of control in co-endemic areas. The high heterogeneity of malaria in 2013 highlights the importance of surveillance and targeted interventions to accelerate towards elimination.

Repeated mosquito net distributions, improved treatment, and trends in malaria cases in sentinel health facilities in Papua New Guinea

Background

Long-lasting insecticidal nets (LLIN), improved diagnosis and artemisinin-based combination therapy (ACT) have reduced malaria prevalence in Papua New Guinea since 2008. Yet, national incidence trends are inconclusive due to confounding effects of the scale-up of rapid diagnostic tests, and inconsistencies in routine reporting.

Methods

Malaria trends and their association with LLIN and ACT roll-out between 2010 and 2014 in seven sentinel health facilities were analysed. The analysis included 35,329 fever patients. Intervention effects were estimated using regression models.

Results

Malaria incidence initially ranged from 20 to 115/1000 population; subsequent trends varied by site. Overall, LLIN distributions had a cumulative effect, reducing the number of malaria cases with each round (incidence rate ratio ranging from 0.12 to 0.53 in five sites). No significant reduction was associated with ACT introduction. Plasmodium falciparum remained the dominant parasite in all sentinel health facilities. Resurgence occurred in one site in which a shift to early and outdoor biting of anophelines had previously been documented.

Conclusions

LLINs, but not ACT, were associated with reductions of malaria cases in a range of settings, but sustainability of the gains appear to depend on local factors. Malaria programmes covering diverse transmission settings such as Papua New Guinea must consider local heterogeneity when choosing interventions and ensure continuous monitoring of trends.

Determinants of long-lasting insecticidal net ownership and utilization in malaria transmission regions: evidence from Zimbabwe Demographic and Health Surveys

Background

Long-lasting insecticidal nets (LLINs) were first introduced in 2010 as a vector control intervention, to complement indoor residual spraying, to reduce malaria transmission in Zimbabwe. The objective of this study was to investigate factors that were associated with LLIN ownership and utilization among households in malaria transmission regions of Zimbabwe.

Methods

A secondary analysis of cross sectional data from the Zimbabwe demographic and health survey (ZDHS) conducted in 2010 and 2015 surveys round was conducted. The analysis used household-level datasets from across the country to generate evidence for the study. Univariate analysis was used to yield descriptive statistics. Principal component analysis (PCA) was used to calculate wealth quintiles. Binary logistic regression approach was used to identify determinants of LLIN ownership and utilization after controlling for other factors. Data analyses were conducted using STATA version 14 software.

Results

There were no major changes in demographic characteristics of households sampled between 2010 and 2015 survey cycles. LLIN ownership increased significantly by 42 percentage points from 2010 to 2015. There was a tremendous increase in universal coverage of LLINs between 2010 and 2015. The overall utilization levels of LLINs among children under-5 years decreased by 11 percentage points between 2010 and 2015. LLIN usage amongst households followed the same trend with that of the under-fives. Using logistic regression model for 2015 data, region/province, type of place of residence, availability of electricity, radio, roof type, gender of head of household, having telephone, type of cooking fuel, presence of mobile phone, owning a bank account, IRS spraying in the previous 12 months, wealth index, and satellite television decorder were independently associated with net ownership among households. Type of place of residence, age of household head, type of cooking fuel, IRS in previous 12 months, and pregnancy were associated with LLIN utilization.

Conclusion

This study revealed increasing LLIN coverage and low usage in malaria-transmission regions of Zimbabwe. Strengthening of LLIN campaigns, social behaviour change communication (SBCC) interventions and programme routine monitoring are recommended.

Mathematical modelling of the impact of expanding levels of malaria control interventions on Plasmodium vivax

Plasmodium vivax poses unique challenges for malaria control and elimination, notably the potential for relapses to maintain transmission in the face of drug-based treatment and vector control strategies. We developed an individual-based mathematical model of P. vivax transmission calibrated to epidemiological data from Papua New Guinea (PNG). In many settings in PNG, increasing bed net coverage is predicted to reduce transmission to less than 0.1% prevalence by light microscopy, however there is substantial risk of rebounds in transmission if interventions are removed prematurely. In several high transmission settings, model simulations predict that combinations of existing interventions are not sufficient to interrupt P. vivax transmission. This analysis highlights the potential options for the future of P. vivax control: maintaining existing public health gains by keeping transmission suppressed through indefinite distribution of interventions; or continued development of strategies based on existing and new interventions to push for further reduction and towards elimination.

Status of Insecticide Resistance in Papua New Guinea: An Update from Nation-Wide Monitoring of Anopheles Mosquitoes

Insecticide resistance (IR) monitoring is an important component of vector-borne disease control. The last assessment of IR in Papua New Guinea (PNG) was conducted in 2010. Since then, vector populations have been exposed to higher levels of pyrethroids with the continued nation-wide distribution of insecticide-treated nets. Here, we provide an update on phenotypic IR in four highly malaria-endemic areas of PNG. IR against deltamethrin, lambda-cyhalothrin, and dichlorodiphenyltrichloroethane was assessed using World Health Organization bioassays. A total of 108 bioassays for each insecticide were conducted screening 2,290 adult female anopheline mosquitoes. No phenotypic resistance was observed. Bioassay parameters agreed well with those observed in other studies that used the same assays and insecticides. These results indicate that the three tested insecticides are still universally effective in PNG. Continued IR monitoring (every 1-2 years) in PNG is recommended to detect reduced susceptibility early and adjust guidelines to prevent widespread resistance.

Insecticide-treated nets and malaria prevalence, Papua New Guinea, 2008-2014

Objective

To investigate changes in malaria prevalence in Papua New Guinea after the distribution of long-lasting Insecticide-treated nets, starting in 2004, and the introduction of artemisinin-based combination therapy in 2011.

Methods

Two malaria surveys were conducted in 2010–2011 and 2013–2014. They included 77 and 92 randomly selected villages, respectively. In each village, all members of 30 randomly selected households gave blood samples and were assessed for malaria infection by light microscopy. In addition, data were obtained from a malaria survey performed in 2008–2009.

Results

The prevalence of malaria below 1600 m in altitude decreased from 11.1% (95% confidence interval, CI: 8.5–14.3) in 2008–2009 to 5.1% (95% CI 3.6–7.4) in 2010–2011 and 0.9% (95% CI 0.6–1.5) in 2013–2014. Prevalence decreased with altitude. Plasmodium falciparum was more common than P. vivax overall, but not everywhere, and initially the prevalence of P. vivax infection decreased more slowly than P. falciparum infection. Malaria infections were clustered in households. In contrast to findings in 2008–2009, no significant association between net use and prevalence was found in the later two surveys. The prevalence of both fever and splenomegaly also decreased but their association with malaria infection became stronger.

Conclusion

Large-scale insecticide-treated net distribution was associated with an unprecedented decline in malaria prevalence throughout Papua New Guinea, including epidemic-prone highland areas. The decline was accompanied by broader health benefits, such as decreased morbidity. Better clinical management of nonmalarial fever and research into residual malaria transmission are required.

The complex relationship of exposure to new Plasmodium infections and incidence of clinical malaria in Papua New Guinea

The molecular force of blood-stage infection (_molFOB) is a quantitative surrogate metric for malaria transmission at population level and for exposure at individual level. Relationships between _molFOB, parasite prevalence and clinical incidence were assessed in a treatment-to-reinfection cohort, where P.vivax (Pv) hypnozoites were eliminated in half the children by primaquine (PQ). Discounting relapses, children acquired equal numbers of new P. falciparum (Pf) and Pv blood-stage infections/year (Pf-_molFOB = 0–18, Pv-_molFOB = 0–23) resulting in comparable spatial and temporal patterns in incidence and prevalence of infections. Including relapses, Pv-_molFOB increased >3 fold (relative to PQ-treated children) showing greater heterogeneity at individual (Pv-_molFOB = 0–36) and village levels. Pf- and Pv-_molFOB were strongly associated with clinical episode risk. Yearly Pf clinical incidence rate (IR = 0.28) was higher than for Pv (IR = 0.12) despite lower Pf-_molFOB. These relationships between _molFOB, clinical incidence and parasite prevalence reveal a comparable decline in Pf and Pv transmission that is normally hidden by the high burden of Pv relapses.

Clinical trial registration: ClinicalTrials.gov NCT02143934

Malaria is caused by five different species of parasites that are transmitted to humans by bites from parasite-carrying mosquitos. Once in human blood, the parasites rapidly multiply. People who live in countries where malaria is common may become infected and never show any symptoms because their immune systems are able to keep parasite numbers low. Repeated infections, or infection with more than one species of malaria parasite also are common. Some species of malaria, including Plasmodium vivax, can hibernate in the liver for weeks or months after the infection and only become active later.

Asymptomatic infections, multi-parasite infections, and reactivating parasites make it hard to measure how often new malaria infections occur. One way scientists can determine if a new infection has occurred is by genotyping the parasites in a person’s blood. Genotyping involves looking for small differences in the parasite DNA. For example, a study in Papua New Guinea, where P. vivax is very common, showed that reactivations of hibernating parasites were more common than new infections.

Now, Hofmann et al. use the same study in Papua New Guinea to compare the frequency and consequences of new infections with P. vivax and another malaria parasite, Plasmodium falciparum. In the study, 466 children from 6 villages were followed for 8 months with tests every 2 to 4 weeks to genotype the parasites in their blood. Some of the children were treated with antimalarial drugs to help wipe out any existing parasites including hibernating ones. While P. vivax was about twice as common in blood samples—likely due to reactivation—genotyping showed that new infections with the two parasites occur at equal rates and often at the same times and locations.

Hofmann et al. also showed that some villages and some children had much higher rates of infection than others. This difference could not fully be explained by use of bednets or other preventive measures. Children were more likely to become ill from P. falciparum than P. vivax even though P. vivax was more common. But children with more frequent infections with P. falciparum seemed better able to manage the parasites and were less likely to develop symptoms that those with infrequent infections. The experiments show that genotyping may help scientists better track new malaria infections and develop better strategies to prevent or treat malaria.

Health information system strengthening and malaria elimination in Papua New Guinea

Background

The objective of the study was to describe an m-health initiative to strengthen malaria surveillance in a 184-health facility, multi-province, project aimed at strengthening the National Health Information System (NHIS) in a country with fragmented malaria surveillance, striving towards enhanced control, pre-elimination.

Methods

A remote-loading mobile application and secure online platform for health professionals was created to interface with the new system (eNHIS). A case-based malaria testing register was developed and integrated geo-coded households, villages and health facilities. A malaria programme management dashboard was created, with village-level malaria mapping tools, and statistical algorithms to identify malaria outbreaks.

Results

Since its inception in 2015, 160,750 malaria testing records, including village of residence, have been reported to the eNHIS. These case-based, geo-coded malaria data are 100% complete, with a median data entry delay of 9 days from the date of testing. The system maps malaria to the village level in near real-time as well as the availability of treatment and diagnostics to health facility level. Data aggregation, analysis, outbreak detection, and reporting are automated.

Conclusions

The study demonstrates that using mobile technologies and GIS in the capture and reporting of NHIS data in Papua New Guinea provides timely, high quality, geo-coded, case-based malaria data required for malaria elimination. The health systems strengthening approach of integrating malaria information management into the eNHIS optimizes sustainability and provides enormous flexibility to cater for future malaria programme needs.

Long-term acceptability, durability and bio-efficacy of ZeroVector® durable lining for vector control in Papua New Guinea

Background

This study examined the acceptability, durability and bio-efficacy of pyrethroid-impregnated durable lining (DL) over a three-year period post-installation in residential homes across Papua New Guinea (PNG).

Methods

ZeroVector^® ITPS had previously been installed in 40 homes across four study sites representing a cross section of malaria transmission risk and housing style. Structured questionnaires, DL visual inspections and group interviews (GIs) were completed with household heads at 12- and 36-months post-installation. Three DL samples were collected from all households in which it remained 36-months post-installation to evaluate the bio-efficacy of DL on Anopheles mosquitoes. Bio-efficacy testing followed WHO guidelines for the evaluation of indoor residual spraying.

Results

The DL was still intact in 86 and 39% of study homes at the two time periods, respectively. In homes in which the DL was still intact, 92% of household heads considered the appearance at 12-months post installation to be the same as, or better than, that at installation compared to 59% at 36-months post-installation. GIs at both time points confirmed continuing high acceptance of DL, based in large part of the perceived attractiveness and functionality of the material. However, participants frequently asserted that they, or their family members, had ceased or reduced their use of mosquito nets as a result of the DL installation. A total of 16 houses were sampled for bio-efficacy testing across the 4 study sites at 36-months post-installation. Overall, combining all sites and samples, both knock-down at 30 min and mortality at 24 h were 100%.

Conclusions

The ZeroVector^® DL installation remained highly acceptable at 36-months post-installation, the material and fixtures proved durable and the efficacy against malaria vectors did not decrease. However, the DL material had been removed from over 50% of the original study homes 3 years post-installation, largely due to deteriorating housing infrastructure. Furthermore, the presence of the DL installation appeared to reduce ITN use among many participating householders. The study findings suggest DL may not be an appropriate vector control method for large-scale use in the contemporary PNG malaria control programme.

The Epidemiology of Malaria in Kutubu, Southern Highlands Province, Papua New Guinea, before and during a Private Sector Initiative for Malaria Control

Papua New Guinea (PNG) has a significant malaria burden, is resource constrained, and has isolated populations with limited access to health services. Home-based management is a key element of the national program that supports strategies of early detection, diagnosis and treatment. We describe the epidemiology of malaria near Lake Kutubu in the Southern Highlands Province through reported data on suspected and confirmed malaria in patients accessing public health facilities or using a novel, incentivised, social marketing approach for malaria treatment at the village level. Monthly case data reported by nine health facilities and 14 village-based providers, known as Marasin Stoa Kipas (MSK), were extracted from outpatient registers and MSK malaria case forms. Descriptive statistics of diagnostic use, monthly incidence, test positivity rate and species distribution were estimated. Summary statistics of service delivery demonstrate patient access and diagnostic coverage in program areas. From May 2005 to September 2013, 15,726 individuals were tested with either rapid diagnostic test and/or microscopy at health facilities, and 42% had a positive result for malaria (n = 6604); of these 67.1% (n = 4431) were positive for P. falciparum (alone or mixed) and 32.9% were positive for non-P. falciparum species (alone or mixed). From October 2007 to September 2013, 9687 individuals were tested with either RDT and/or microscopy at MSK sites and 44.2% (n = 4283) tested positive for malaria; of these, 65.3% (n = 2796) were positive for P. falciparum, while 34.7% (n = 1487) were positive for non-P. falciparum species. Up to April 2010 there was an intermittent and upward trend in the reported incidence of all species of confirmed malaria, reaching 50 per 1000 population per month for both sites combined, followed by a steady decline to four per 1000 population per month in 2013, with P. vivax the most common infection. This study is the most recent longitudinal overview of malaria in the Southern Highlands since 2003. It outlines patient access to a community-based model of care. The analysis shows changes in health facility versus MSK use, a strongly decreasing trend in incidence of confirmed malaria from 2010 to 2013, and a shift from predominantly P. falciparum to P. vivax infection.

Spatial Effects on the Multiplicity of Plasmodium falciparum Infections

As malaria is being pushed back on many frontiers and global case numbers are declining, accurate measurement and prediction of transmission becomes increasingly difficult. Low transmission settings are characterised by high levels of spatial heterogeneity, which stands in stark contrast to the widely used assumption of spatially homogeneous transmission used in mathematical transmission models for malaria. In the present study an individual-based mathematical malaria transmission model that incorporates multiple parasite clones, variable human exposure and duration of infection, limited mosquito flight distance and most importantly geographically heterogeneous human and mosquito population densities was used to illustrate the differences between homogeneous and heterogeneous transmission assumptions when aiming to predict surrogate indicators of transmission intensity such as population parasite prevalence or multiplicity of infection (MOI). In traditionally highly malaria endemic regions where most of the population harbours malaria parasites, humans are often infected with multiple parasite clones. However, studies have shown also in areas with low overall parasite prevalence, infection with multiple parasite clones is a common occurrence. Mathematical models assuming homogeneous transmission between humans and mosquitoes cannot explain these observations. Heterogeneity of transmission can arise from many factors including acquired immunity, body size and occupational exposure. In this study, we show that spatial heterogeneity has a profound effect on predictions of MOI and parasite prevalence. We illustrate, that models assuming homogeneous transmission underestimate average MOI in low transmission settings when compared to field data and that spatially heterogeneous models predict stable transmission at much lower overall parasite prevalence. Therefore it is very important that models used to guide malaria surveillance and control strategies in low transmission and elimination settings take into account the spatial features of the specific target area, including human and mosquito vector distribution.

Prevalence of malaria across Papua New Guinea after initial roll-out of insecticide-treated mosquito nets

OBJECTIVES

To assess the population prevalence of malaria in villages across Papua New Guinea (PNG) following the first roll-out of free long-lasting insecticidal nets (LLIN).

METHODS

Between October 2008 and August 2009, a household survey was conducted in 49 random villages in districts covered by the LLIN distribution campaign. The survey extended to 19 villages in sentinel sites that had not yet been covered by the campaign. In each village, 30 households were randomly sampled, household heads were interviewed and capillary blood samples were collected from all consenting household members for microscopic diagnosis of malaria.

RESULTS

Malaria prevalence ranged from 0% to 49.7% with a weighted average of 12.1% (95% CI 9.5, 15.3) in the national sample. More people were infected with Plasmodium falciparum (7.0%; 95% CI 5.4, 9.1) than with P. vivax (3.8%; 95% CI 2.4, 5.7) or P. malariae (0.3%; 95% CI 0.1, 0.6). Parasitaemia was strongly age-dependent with a P. falciparum peak at age 5-9 years and a P. vivax peak at age 1-4 years, yet with differences between geographical regions. Individual LLIN use and high community coverage were associated with reduced odds of infection (OR = 0.64 and 0.07, respectively; both P < 0.001). Splenomegaly in children and anaemia were common morbidities attributable to malaria.

CONCLUSIONS

Malaria prevalence across PNG is again at levels comparable to the 1970s. The strong association of LLIN use with reduced parasitaemia supports efforts to achieve and maintain high country-wide coverage. P. vivax infections will require special targeted approaches across PNG.

Patterns and predictive factors of long-lasting insecticidal net usage in a previously high malaria endemic area in Sri Lanka: a cross-sectional survey

BACKGROUND

Long-lasting insecticidal nets (LLINs) have been widely distributed in Sri Lanka for malaria control. Their effectiveness depends on proper utilisation and maintenance at the household level.

METHODS

A cross-sectional study was performed to examine the patterns and predictive factors of LLIN maintenance and use in Anuradhapura district. Data was collected and analysed from 530 LLIN-owning households, selected by a multi-stage cluster sampling technique. Multivariable logistic regression identified factors associated with proper maintenance at the household level. Hierarchical linear modelling identified factors associated with LLIN use the previous night.

RESULTS

Almost 75% (377/504) of households had used all their LLINs the previous night, while 82.9% (418/504) had used at least one. Only 3.2% (15/474) were maintaining the LLIN in such a way as to maximise its insecticidal efficacy. Six variables were significantly associated (p<0.05) with use the previous night: more residents, fewer plain nets, reporting practical benefits of LLINs, conical shape, newer nets and lack of side effects. Two variables were significantly associated with proper maintenance: increasing level of education and taking safety precautions while washing.

CONCLUSIONS

Results suggest LLIN practices could improve in settings of low malaria transmission if distribution programmes took into account recipient preferences, promoted LLIN use over plain nets, and emphasised the techniques and significance of proper net maintenance.

Whole-genome sequencing reveals absence of recent gene flow and separate demographic histories for Anopheles punctulatus mosquitoes in Papua New Guinea

Anopheles mosquitoes are the vectors of several human diseases including malaria. In many malaria endemic areas, several species of Anopheles coexist, sometimes in the form of related sibling species that are morphologically indistinguishable. Determining the size and organization of Anopheles populations, and possible ongoing gene flow among them is important for malaria control and, in particular, for monitoring the spread of insecticide resistance alleles. However, these parameters have been difficult to evaluate in most Anopheles species due to the paucity of genetic data available. Here, we assess the extent of contemporary gene flow and historical variations in population size by sequencing and de novo assembling the genomes of wild-caught mosquitoes from four species of the Anopheles punctulatus group of Papua New Guinea. Our analysis of more than 50 Mb of orthologous DNA sequences revealed no evidence of contemporary gene flow among these mosquitoes. In addition, investigation of the demography of two of the An. punctulatus species revealed distinct population histories. Overall, our analyses suggest that, despite their similarities in morphology, behaviour and ecology, contemporary sympatric populations of An. punctulatus are evolving independently.