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Randomized Controlled Trial
. 2018 Aug;99(2):350-356.
doi: 10.4269/ajtmh.18-0081. Epub 2018 May 31.

Anopheles Salivary Biomarker as a Proxy for Estimating Plasmodium falciparum Malaria Exposure on the Thailand-Myanmar Border

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Free PMC article
Randomized Controlled Trial

Anopheles Salivary Biomarker as a Proxy for Estimating Plasmodium falciparum Malaria Exposure on the Thailand-Myanmar Border

Phubeth Ya-Umphan et al. Am J Trop Med Hyg. .
Free PMC article

Abstract

Timely identification and treatment of malaria transmission "hot spots" is essential to achieve malaria elimination. Here we investigate the relevance of using an Anopheles salivary biomarker to estimate Plasmodium falciparum malaria exposure risk along the Thailand-Myanmar border to guide malaria control. Between May 2013 and December 2014, > 9,000 blood samples collected in a cluster randomized control trial were screened with serological assays to measure the antibody responses to Anopheles salivary antigen (gSG6-P1) and P. falciparum malaria antigens (circumsporozoite protein, merozoite surface protein 119 [MSP-119]). Plasmodium falciparum infections were monitored through passive and active case detection. Seroprevalence to gSG6-P1, MSP-119, and CSP were 71.8% (95% Confidence interval [CI]: 70.9, 72.7), 68.6% (95% CI: 67.7, 69.5), and 8.6% (95% CI: 8.0, 9.2), respectively. Multivariate analysis showed that individuals with the highest Ab response to gSG6-P1 had six times the odds of being positive to CSP antigens (P < 0.001) and two times the odds of P. falciparum infection compared with low gSG6-P1 responders (P = 0.004). Spatial scan statistics revealed the presence of clusters of gSG6-P1 that partially overlapped P. falciparum infections. The gSG6-P1 salivary biomarker represents a good proxy for estimating P. falciparum malaria risk and could serve to implement hot spot-targeted vector control interventions to achieve malaria elimination.

Figures

Figure 1.
Figure 1.
Seroprevalence data with 95% confidence interval for antibodies against Plasmodium falciparum merozoite surface protein 119 (MSP-119), and P. falciparum sporozoite (CSP), according to villages Ka Nu Hta, Tar Au Ta, Htee Kaw Taw, and Htoo Pyin Nyar (KNH, TOT, HKT, and TPN) and surveys (seven surveys over 18 months). Seropositivity for MSP-119 and CSP was calculated based on cut-off values (ΔOD) > 0.162 and > 0.115, respectively. OD = optical density.
Figure 2.
Figure 2.
Micogeographical clusters of Pf malaria infections and vector exposure in the study villages at baseline (M0) and then after the implementation of the mass drug adminsitration (MDA) pilot trial (M15). The large red (Plasmodium falciparum infections as measured by either ultrasensitive qPCR or rapid diagnostic test) and green (very high responder to gSG6-P1) circles are the statistically significant hotspots detected by spatial scan statistics (P < 0.001). Pf infections are shown in red diamonds. Before MDA (M0), three villages Tar Au Ta, Ka Nu Hta, and Htee Kaw Taw (TOT, KNH, and HKT) had multiple clusters of gSG6-P1 responders (Relative Risk [RR] = 16.15, 9.29, 8.83, and, P < 0.0001, respectively) that partially overlapped with clusters of P. falciparum infections at KNH (RR = 30.20, P < 0.0001) and HKT (RR = 19.46, P < 0.0001). After MDA (M15 conducted at the end of the rainy season), P. falciparum infections almost disappeared in all villages except at TOT where a cluster of P. falciparum infections was detected in the western part of the village (RR = 77.23, P < 0.0001) that mostly overlapped with the cluster of gSG6-P1 (RR = 5.86, P < 0.0001).

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