Community-based molecular and serological surveillance of subclinical malaria in Myanmar

Abstract

Background In the Greater Mekong Subregion (GMS), current malaria surveillance strategies rely on a network of village health volunteers (VHVs) reporting the results of rapid diagnostic tests (RDTs), known to miss many asymptomatic infections. Integration of more sensitive diagnostic molecular and serological measures into the VHV network may improve surveillance of residual malaria transmission in hard-to-reach areas in the region and inform targeted interventions and elimination responses. However, data on residual malaria transmission that would be captured by these measures in the VHV-led testing and treatment surveillance network in the GMS is unknown. Methods A total of 114 VHVs were trained to collect dried blood spots from villagers undergoing routine RDTs as part of VHV-led active and passive case detection from April 2015 to June 2016. Samples were subjected to molecular testing (quantitative polymerase chain reaction [qPCR]) to determine Plasmodium falciparum and P. vivax infection and serological testing (against P. falciparum and P. vivax antigens) to determine exposure to P. falciparum and P. vivax. Results Over 15 months, 114 VHVs performed 32,194 RDTs and collected samples for molecular (n = 13,157) and serological (n = 14,128) testing. The prevalence of molecular-detectable P. falciparum and P. vivax infection was 3.2% compared to the 0.16% prevalence of Plasmodium spp. by RDT, highlighting the large burden of infections undetected by standard surveillance. Peaks in anti-P. falciparum, but not P. vivax, merozoite IgG seroprevalence coincided with seasonal P. falciparum transmission peaks, even in those with no molecularly detectable parasites. At the individual level, antibody seropositivity was associated with reduced odds of contemporaneous P. falciparum (OR for PfCSP 0.51 [95%CI 0.35, 0.76], p = 0.001, PfAMA1 0.70 [95%CI 0.52, 0.93], p = 0.01, and PfMSP2 0.81 [95%CI 0.61, 1.08], p = 0.15), but not P. vivax infection (OR PvAMA1 1.02 [95%CI 0.73, 1.43], p = 0.89) indicating a potential role of immunity in protection against molecular-detectable P. falciparum parasitaemia. Conclusions We demonstrated that integration and implementation of sample collection for molecular and serological surveillance into networks of VHV servicing hard-to-reach populations in the GMS is feasible, can capture significant levels of ongoing undetected seasonal malaria transmission and has the potential to supplement current routine RDT testing. Improving malaria surveillance by advancing the integration of molecular and serological techniques, through centralised testing approaches or novel point-of-contact tests, will advance progress, and tracking, towards malaria elimination goals in the GMS.

Hyper-prevalence of submicroscopic Plasmodium falciparum infections in a rural area of western Kenya with declining malaria cases

“…These infections also show reduced parasite genetic diversity [ 9 ], fewer infective Anopheles [ 10 , 11 ], lower adherence to anti-malarials drug regimens [ 12 – 14 ], and increased asexual parasite clearance rates [ 9 , 15 ]. Previous studies of submicroscopic parasitaemia have primarily been concerned with its occurrence in pregnant women [ 16 – 20 ] and cross-sectional community surveys of asymptomatic individuals [ 3 , 21 – 24 ]. However, fewer studies have focused on its occurrence as it pertains to malaria treatment-seeking behaviour [ 14 , 25 , 26 ].…”

Reducing malaria transmission in forest-going mobile and migrant populations in Lao PDR and Cambodia: protocol for stepped-wedge cluster-randomised controlled trial

“…Used RDT cassettes and dried blood spots will be kept and stored where possible to extract DNA and antibodies to determine secondary outcomes 2B, 2C, 2D, 2E, 2F, and 2G using PCR and ELISA methods as previously described [ 16 , 19 – 21 ].…”

The role of naturally acquired antimalarial antibodies in subclinicalPlasmodiumspp. infection

“…This caveat is particularly problematic in cross‐sectional surveys, where it is impossible to know when the last boosting event occurred, and how the development and kinetics of that response will change the association over time. Further, in regions that have recently transitioned from high/moderate to low transmission where a large proportion of a surveyed population may still be reflected as high responders or as seropositive 71 . The findings of such investigations may provide interesting insight, however, large, observational studies using highly sensitive molecular diagnoses with frequent sampling among returning participants provide the most robust data for assessing associations between acquired immunity and subclinical infection.…”

“…Recent studies have demonstrated an association between Abs and protection from PCR‐detectable subclinical infection. 70 , 71 However, these findings have been reported mostly in serial cross‐sectional surveys, which may fail to capture individual infection dynamics.…”

“…Further, in regions that have recently transitioned from high/moderate to low transmission where a large proportion of a surveyed population may still be reflected as high responders or as seropositive. 71 The findings of such investigations may provide interesting insight, however, large, observational studies using highly sensitive molecular diagnoses with frequent sampling among returning participants provide the most robust data for assessing associations between acquired immunity and subclinical infection. Longitudinal studies can provide stronger evidence of the role of antibodies in subclinical Plasmodium spp.…”