Validating molecular and serological tools for detecting hidden reservoirs of Plasmodium infections in Papua New Guinea

The Asia-Pacific region has set the target of eliminating malaria by 2030. A significant challenge we face as countries approach elimination is the prevalence of low-density asymptomatic infections that maintain transmission. Currently the effective control of malaria is impeded by the fact that existing surveillance methods are inefficient for detecting low-density infections that do not cause febrile symptoms. New approaches to detect and effectively target areas or populations with ongoing transmission are urgently required. That is where this project comes in. This project will start to address this gap by validating the ability of these tools to track malaria transmission foci across a range of transmission settings in PNG.

Aim 1: We will validate the sensitivity and specificity of serological indicators of recent exposure to Pf and Pv compared to ultra-sensitive PCR (usPCR) parasite prevalence indicator for surveillance using samples from a 2013 East Sepik Province longitudinal child cohort. We will investigate this in 100 children from low-moderate transmission villages of Ilahita 1-4 (incidence of 1.1 genetically distinct Pf infections/child/year and 0.7 Pv infections/child/year) and 100 children from the high transmission villages of Sunuhu 1 and 2 (incidence of 3.57 Pf infections/child/year for Pf and 5.3 Pv infections/child/year). We will measure the prevalence of Pf and Pv infections at monthly timepoints by applying validated ultra-sensitive Pf and Pv PCR assays to samples from these surveys previously determined to be negative by standard qPCR. We will also determine the prevalence of recent exposure to Pf and Pv using a serological screening tool on baseline and endline samples (two timepoints). This screening tool uses validated panels of 4 novel Pf and 4 novel Pv antigens capable of identifying individuals with exposure to Pf or Pv infections will be assessed in both low and high transmission settings by utilising multiplex serology assays run on a MagPix Luminex-based assay platform.

Aim 2: We will apply these novel ultra-sensitive molecular and serological screening tools to samples collected from two community cross sectional surveys in East Sepik Province to identify areas/populations harbouring low-density infections and sustaining transmission. One survey was conducted during a low-moderate transmission period in 2012 (9% Pf prevalence and 6% Pv prevalence by standard qPCR) and one was conducted in 2019 after the recent resurgence (20% Pf prevalence and 30% Pv prevalence by standard qPCR). Ultra-sensitive molecular screening tools will be performed on standard qPCR-negative samples collected in these cross-sectional studies. The validated serological assay (as described above) will be applied to all samples to determine participant’s exposure to malaria in the previous 12 months. The application of serological and molecular screening tools to these surveys will enable us to compare the utility of these indicators at the population level for spatial risk mapping at different transmission intensities.

Data analysis: In all sites, high heterogeneity of Plasmodium spp. prevalence is observed between villages and is sufficient to detect spatial clustering and identify relationships with age, sex, occupation, movement, proximity to vector breeding sites and use of malaria control tools. We will employ a variety of analysis methods including multilevel mixed effects modelling, spatial analyses (e.g., spatial cluster detection using statistics such as the spatial scan statistic; multivariable spatial modelling approaches such as model-based geostatistics) to model the spatial relationships between the different measures of infection (prevalence, multiplicity of infection) and exposure (antibody titres) to Pv and Pf, identifying those with the highest predictive value and spatial resolution. All markers will be compared for their ability to identify locations or populations of high infection risk and to provide sufficient granularity across the different scales for programmatic decision-making.

Asymptomatic Reservoir
Surveillance

Aug 2020 — Oct 2023

$15,000

Australia

Australian Centre for Research Excellence in Malaria Elimination (ACREME)

Malaria Molecular Surveillance (MMS)