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

Asia-Pacific ICEMR: Understanding Malaria Transmission to Accelerate Malaria Elimination in the Asia Pacific Region

Gaining an in-depth understanding of malaria transmission requires integrated, multifaceted research approaches. The Asia-Pacific International Center of Excellence in Malaria Research (ICEMR) is applying specifically developed molecular and immunological assays, in-depth entomological assessments, and advanced statistical and mathematical modeling approaches to a rich series of longitudinal cohort and cross-sectional studies in Papua New Guinea and Cambodia. This is revealing both the essential contribution of forest-based transmission and the particular challenges posed by Plasmodium vivax to malaria elimination in Cambodia. In Papua New Guinea, these studies document the complex host–vector–parasite interactions that are underlying both the stunning reductions in malaria burden from 2006 to 2014 and the significant resurgence in transmission in 2016 to 2018. Here we describe the novel analytical, surveillance, molecular, and immunological tools that are being applied in our ongoing Asia-Pacific ICEMR research program

Naturally acquired antibodies to gametocyte antigens are associated with reduced transmission of Plasmodium vivax gametocytes to Anopheles arabiensis mosquitoes

Naturally acquired antibodies may reduce the transmission of Plasmodium gametocytes to mosquitoes. Here, we investigated associations between antibody prevalence and P. vivax infectivity to mosquitoes. A total of 368 microscopy confirmed P. vivax symptomatic patients were passively recruited from health centers in Ethiopia and supplemented with 56 observations from asymptomatic P. vivax parasite carriers. Direct membrane feeding assays (DMFA) were performed to assess mosquito infectivity; for selected feeds these experiments were also performed after replacing autologous plasma with malaria naïve control serum (n=61). The prevalence of antibodies against 6 sexual stage antigens (Pvs47, Pvs48/45, Pvs230, PvsHAP2, Pvs25 and PvCelTOS) and an array of asexual antigens was determined by ELISA and multiplexed bead-based assays. Gametocyte (ρ< 0.42; p = 0.0001) and parasite (ρ = 0.21; p = 0.0001) densities were positively associated with mosquito infection rates. Antibodies against Pvs47, Pvs230 and Pvs25 were associated with 23 and 34% reductions in mosquito infection rates (p<0.0001), respectively. Individuals who showed evidence of transmission blockade in serum-replacement DMFAs (n=8) were significantly more likely to have PvsHAP2 or Pvs47 antibodies. Further studies may demonstrate causality for the observed associations, improve our understanding of the natural transmission of P. vivax and support vaccine development

The effect of host plants on genotype variability in fitness and honeydew composition of Aphis fabae

Aphid species can be polyphagous, feeding on multiple host plants across genera. As host plant species can have large variation in their phloem composition, this can affect aphid fitness and honeydew composition. Previous research showed significant intraspecific genotype variation in the composition of the honeydew carbohydrates of the black bean aphid Aphis fabae, with the ant attractant trisaccharide melezitose showing especially large variation across different genotypes. In this study, we test if variation in melezitose and carbohydrate composition of aphid honeydew could be linked to the adaptation of specific aphid genotypes to particular host plants. To this end, 4 high and 5 low melezitose secreting genotypes of the black bean aphid Aphis fabae were reared on 4 common host plants: broad bean, goosefoot, beet, and poppy. The carbohydrate composition, and in particular melezitose secretion, showed important aphid genotype and host plant interactions, with some genotypes being high melezitose secreting on 1 host plant but not on another. However, the interaction effects were not paralleled in the fitness measurements, even though there were significant differences in the average fitness across the different host plants. On the whole, this study demonstrates that aphid honeydew composition is influenced by complex herbivore-plant interactions. We discuss the relevance of these findings in the context of ant-aphid mutualisms and adaptive specialization in aphids.status: publishe

The influence of facultative endosymbionts on honeydew carbohydrate and amino acid composition of the black bean aphid Aphis fabae

The facultative endosymbionts Hamiltonella defensa and Regiella insecticola are commonly found in aphids. They are linked with various ecological benefits but generally occur at low prevalence, which indicates a possible harbouring cost. Little is known about how the presence of facultative endosymbionts is reflected in honeydew composition. Honeydew is the key mediator of the mutualism between aphids and their tending ants. The present study examines whether endosymbionts have an influence on aphid honeydew quality by comparing the amino acid and carbohydrate concentrations between infected and uninfected aphids. To this end, two genetic lines of the aphid Aphis fabae Scopoli are experimentally infected with different strains of Hamiltonella and Regiella. Infected aphids are shown to have reduced concentrations of amino acids in the honeydew compared with uninfected aphids. However, the presence of endosymbionts has no effect on the absolute amount of carbohydrates produced. Nevertheless, interclonal variation in honeydew composition between aphid genotypes is observed for both carbohydrate and amino acid production. These results imply that the nutritional value of honeydew depends on aphid genotype, as well as on the presence of secondary bacterial endosymbionts, which suggests that there is a physiological cost of harbouring endosymbionts and which could also impact aphid attractiveness to tending ants.status: publishe

The influence of facultative endosymbionts on honeydew carbohydrate and amino acid composition of the black bean aphid Aphis fabae

The facultative endosymbionts Hamiltonella defensa and Regiella insecticola are commonly found in aphids. They are linked with various ecological benefits but generally occur at low prevalence, which indicates a possible harbouring cost. Little is known about how the presence of facultative endosymbionts is reflected in honeydew composition. Honeydew is the key mediator of the mutualism between aphids and their tending ants. The present study examines whether endosymbionts have an influence on aphid honeydew quality by comparing the amino acid and carbohydrate concentrations between infected and uninfected aphids. To this end, two genetic lines of the aphid Aphis fabaeScopoli are experimentally infected with different strains of Hamiltonella and Regiella. Infected aphids are shown to have reduced concentrations of amino acids in the honeydew compared with uninfected aphids. However, the presence of endosymbionts has no effect on the absolute amount of carbohydrates produced. Nevertheless, interclonal variation in honeydew composition between aphid genotypes is observed for both carbohydrate and amino acid production. These results imply that the nutritional value of honeydew depends on aphid genotype, as well as on the presence of secondary bacterial endosymbionts, which suggests that there is a physiological cost of harbouring endosymbionts and which could also impact aphid attractiveness to tending ants

The cost of ant-attendance and melezitose secretion in the black bean aphid Aphis fabae

1. The aphid Aphis fabae (Scopoli) is facultatively tended by Lasius niger (Linnaeus) ants. Previously, we found that A. fabae colonies can be made up of several clones, and that clones display significant differences in the composition of their honeydew sugars, especially in the amount of the ant attractant sugar melezitose that they produce. 2. These clonal differences could greatly impact the strength of the mutualistic interaction with ants as well as the aphids' fitness. 3. Hence, the aim of this study was to compare the fitness of different A. fabae clones that differed in their melezitose secretion, and whether or not they were tended by ants. 4. We analyzed individual fitness indices, colony growth and alate production of single-clone aphid colonies. 5. Our results demonstrate that the fitness consequences of ant attendance critically depend on an interaction with levels of melezitose production. In particular, we show that high-melezitose secreting clones produce fewer alates and hence might have a lower dispersal ability in the presence of ants. 6. Furthermore, our data confirm previous evidence that ant attendance is costly and results in the production of fewer apterae.status: publishe

Similarity-based Neuro-Fuzzy Networks and Genetic Algorithms in Time Series Models Discovery

This paper presents a hybrid soft computing technique for the study of time varying processes based on a combination of neurofuzzy techniques with evolutionary algorithms, in particular, genetic algorithms . Two problems are simultaneously addressed: the discovery of patterns of dependency in general multivariate dynamic systems (in an optimal or quasi-optimal sense), and the construction of a suitable initial representation for the function expressing the dependencies for the best model found. The patterns of dependency are represented by general autoregresive models (not necessarily linear), relating future values of a target variable with its past values as well as with those of the other observed variables. These patterns of dependencies are explored with genetic algorithm, whereas the functional approximation is constructed with a neurofuzzy heterogeneous network. The particular kind of neurofuzzy network chosen uses a nonclassical neuron model based on similarity in the hidden layer, and a classical neuron model in the output layer. An instance-based training approach allows a rapid construction of a complete network from the multivariate signal set and the dependency pattern under exploration, thus allowing the investigation of many prospective patterns in a short time. The main goal of the technique is the rapid prototyping and characterization of interesting or relevant interdependencies, especially in poorly known complex multivariate processes. The genetic search of the space of possible models (astronomically huge in most practical problems) doesn't guarantee the optimality of the models discovered. However, it provides a set of plausible dependency patterns explaining the interactions taking place, which can be refined later on by using more sophisticated techniques (also more time consuming) as function approximators, to improve the quality of the forecasting operator. Examples with known time series show that the proposed approach gives better results than the classical statistical one.Nous pr\ue9sentons une technique de calcul hybride \uab\ua0souple\ua0\ubb pour l'\ue9tude des processus chronologiques, combinant des techniques neuro-floues et des algorithmes \ue9volutionnaires, notamment des algorithmes g\ue9n\ue9tiques. Deux probl\ue8mes sont abord\ue9s simultan\ue9ment : (1) la d\ue9couverte de motifs de d\ue9pendance dans les syst\ue8mes dynamiques g\ue9n\ue9raux multivari\ue9s (dans un sens optimal ou quasi optimal) et (2) la construction d'une repr\ue9sentation initiale convenable pour la fonction exprimant les d\ue9pendances du meilleur syst\ue8me trouv\ue9. Les motifs de d\ue9pendance sont repr\ue9sent\ue9s par des mod\ue8les autor\ue9gressifs g\ue9n\ue9raux (pas n\ue9cessairement lin\ue9aires) reliant les valeurs ult\ue9rieures d'une variable cible avec ses valeurs ant\ue9rieures et celles d'autres valeurs observ\ue9es. L'algorithme g\ue9n\ue9tique explore ces motifs de d\ue9pendance alors qu'un r\ue9seau neuro-flou h\ue9t\ue9rog\ue8ne construit l'approximation fonctionnelle. Le r\ue9seau neuro-flou choisi comprend dans sa couche cach\ue9e, un mod\ue8le de neurones non classiques bas\ue9s sur la similitude et, dans sa couche de sortie, un mod\ue8le de neurones classiques. L'entra\ueenement bas\ue9 sur les instances permet d'\ue9laborer rapidement un r\ue9seau complet \ue0 partir de l'ensemble des signaux multivari\ue9s et le motif de d\ue9pendance explor\ue9, ce qui permet d'explorer plusieurs motifs possibles dans un temps court. Cette technique a pour objectif principal le prototypage rapide et la caract\ue9risation d'interd\ue9pendances int\ue9ressantes ou appropri\ue9es, notamment pour les processus multivari\ue9s complexes et mal connus. L'exploration g\ue9n\ue9tique de l'univers des mod\ue8les possibles (d'une taille astronomique dans la plupart des cas pratiques) ne garantit pas que les mod\ue8les d\ue9couverts soient optimaux. Toutefois, elle donne un ensemble de motifs de d\ue9pendance plausibles qui expliquent les interactions en cours. Pour am\ue9liorer la qualit\ue9 de l'op\ue9rateur de pr\ue9diction, on pourra raffiner ult\ue9rieurement cet ensemble \ue0 l'aide de techniques plus complexes (mais aussi plus lentes) comme les approximateurs de fonction. Nos calculs sur des fonctions chronologiques connues ont montr\ue9 que l'approche propos\ue9e donnait de meilleurs r\ue9sultats que l'approche statistique classique.NRC publication: Ye

Therapeutic and Transmission-Blocking Efficacy of Dihydroartemisinin/Piperaquine and Chloroquine against Plasmodium vivax Malaria, Cambodia

We assessed the efficacy of standard 3-day courses of chloroquine and dihydroartemisinin/piperaquine against Plasmodium vivax malaria. Compared with chloroquine, dihydroartemisinin/piperaquine was faster in clearing asexual P. vivax parasites and blocking human-to-mosquito transmission. This drug combination was also more effective in preventing potential recurrences for >2 months

Amplification of Duffy binding protein-encoding gene allows Plasmodium vivax to evade host anti-DBP humoral immunity

International audienceAntigenic variation, the capacity to produce a range of variable antigens, is a well-described strategy of Plasmodium and other parasites to evade host immunity. Here, we show that gene amplification is an additional evasion mechanism used by Plasmodium vivax to escape humoral immunity targeting PvDBP, the key ligand involved in reticulocyte invasion. PvDBP gene amplification leads to increased mRNA levels and protects P. vivax in vitro against invasion inhibitory human monoclonal antibodies targeting a conserved binding domain of DBP. Patient samples suggest that parasites with increased pvdbp copy number are able to infect individuals with naturally acquired antibodies highly blocking the binding of PvDBP to the Duffy receptor. These results show that gene copy number variation affect the parasite's ability to evade anti-PvDBP humoral immunity