Antibody responses to a suite of novel serological markers for malaria surveillance demonstrate strong correlation with clinical and parasitological infection across seasons and transmission settings in The Gambia

Abstract

Background As malaria transmission declines, sensitive diagnostics are needed to evaluate interventions and monitor transmission. Serological assays measuring malaria antibody responses offer a cost-effective detection method to supplement existing surveillance tools. Methods A prospective cohort study was conducted from 2013 to 2015 in 12 villages across five administrative regions in The Gambia. Serological analysis included samples from the West Coast Region at the start and end of the season (July and December 2013) and from the Upper River Region in July and December 2013 and April and December 2014. Antigen-specific antibody responses to eight Plasmodium falciparum (P. falciparum) antigens—Etramp5.Ag1, GEXP18, HSP40.Ag1, Rh2.2030, EBA175 RIII-V, PfMSP119, PfAMA1, and PfGLURP.R2—were quantified using a multiplexed bead-based assay. The association between antibody responses and clinical and parasitological endpoints was estimated at the individual, household, and population level. Results Strong associations were observed between clinical malaria and concurrent sero-positivity to Etramp5.Ag1 (aOR 4.60 95% CI 2.98–7.12), PfMSP119 (aOR 4.09 95% CI 2.60–6.44), PfAMA1 (aOR 2.32 95% CI 1.40–3.85), and PfGLURP.R2 (aOR 3.12, 95% CI 2.92–4.95), while asymptomatic infection was associated with sero-positivity to all antigens. Village-level sero-prevalence amongst children 2–10 years against Etramp5.Ag1, HSP40.Ag1, and PfMSP119 showed the highest correlations with clinical and P. falciparum infection incidence rates. For all antigens, there were increased odds of asymptomatic P. falciparum infection in subjects residing in a compound with greater than 50% sero-prevalence, with a 2- to 3-fold increase in odds of infection associated with Etramp5.Ag1, GEXP18, Rh2.2030, PfMSP119, and PfAMA1. For individuals residing in sero-positive compounds, the odds of clinical malaria were reduced, suggesting a protective effect. Conclusions At low transmission, long-lived antibody responses could indicate foci of malaria transmission that have been ongoing for several seasons or years. In settings where sub-patent infections are prevalent and fluctuate below the detection limit of polymerase chain reaction (PCR), the presence of short-lived antibodies may indicate recent infectivity, particularly in the dry season when clinical cases are rare. Serological responses may reflect a persistent reservoir of infection, warranting community-targeted interventions if individuals are not clinically apparent but have the potential to transmit. Therefore, serological surveillance at the individual and household level may be used to target interventions where there are foci of asymptomatically infected individuals, such as by measuring the magnitude of age-stratified antibody levels or identifying areas with clustering of above-average antibody responses across a diverse range of serological markers.

Plasmodium falciparum serology: A comparison of two protein production methods for analysis of antibody responses by protein microarray

“…Despite the lack of a clearly defined relationship between antigen-matched targets from opposing expression systems, we remain confident that microarrays utilising IVTT or purified recombinant proteins are able to produce compelling and biologically relevant data. Indeed, our data show age-dependent trends in antibody responses (typical of highly endemic populations [1][2][3]) irrespective of expression system (Supplementary figure 2), lending weight to the applicability of either methodology in serological assays [33][34][35][36][37][38][39][40][41][42][43][44][45][46].…”

Serological evaluation of the effectiveness of reactive focal mass drug administration and reactive vector control to reduce malaria transmission in Zambezi Region, Namibia: Results from a secondary analysis of a cluster randomised trial

“…A subset of eight antigens (Etramp5.Ag1, GEXP18, HSP40.Ag1, Rh2.2030, EBA175, Pf MSP1 19 , Pf AMA1, Pf GLURP.R2) were selected from an initial screen of 856 candidates on an in vitro transcription and translation (IVTT) protein microarray based on their correlation with clinical and parasitological endpoints in previous studies. 12 , 22 Antigens were expressed in Escherichia coli ( E.coli ) as glutathione S-transferase (GST)-tagged fusion proteins, except for Pf AMA1 expressed in Pichia pastoris as a histidine-tagged protein. Non-malaria reactivity against GST-tagged fusion proteins were assessed using IgG responses to GST-coupled beads, and samples with greater than 1000 median fluorescence intensity (MFI) were excluded from analyses due to high non-specific IgG response.…”

“…Serological methods are increasingly being used alongside clinical and parasitological metrics for surveillance. Studies in moderate to low transmission regions across sub-Saharan Africa, including Tanzania, 9 Equatorial Guinea, 10 South Africa 11 and The Gambia, 12 have found that malaria-specific antibody responses are highly correlated with parasitological endpoints. Serological assays can be a particularly useful tool in settings where parasite densities commonly fall below the detection limit of other diagnostics such as microscopy or RDTs.…”

“… 21 The study presented here is an extended trial analysis assessing cluster-level antibody responses to a panel of serological markers previously shown to be associated with parasitological measures of malaria. 12 , 22 …”

“… 23 Etramp5.Ag1 in particular has been shown to be a discriminatory sero-incidence measure between geographical regions and transmission seasons in The Gambia. 12 , 22 However, serological markers of malaria exposure have rarely been used as outcome measures for cluster randomised trials. Etramp5.Ag1 belongs to the early transcribed membrane protein family.…”