Validation of serological markers of recent exposure to <i>Plasmodium vivax</i> in Cambodia: a longitudinal cohort and cross-sectional study.

Abstract

Asymptomatic <i>Plasmodium vivax</i> infections undermine malaria control by sustaining transmission. This study aimed to validate an eight-marker serological panel (selected from 14 antigens) of <i>P. vivax</i> exposure to detect individuals likely harbouring hypnozoites in rural Cambodia, and to compare it with molecular surveillance for identifying at-risk populations in low-transmission settings. Two studies were conducted in Mondulkiri, Cambodia. In a longitudinal cohort (N = 471), participants were tested monthly for one year for <i>P. vivax</i> using qPCR. At 12 months, IgG responses to 14 antigens were assessed, and Random Forest models ('Cambodia-specific' and 'global') were used to classify previous infection, with PCR as the reference standard. In a cross-sectional survey (N = 3538), risk factors for sero- and PCR positivity were assessed using generalized linear mixed-effects models. PCR detected <i>P. vivax</i> in 29.9% (141/471) of participants over the 12-month follow-ups, while 31.8% (150/471) were classified as seropositive at month 12. Of 141 PCR-confirmed cases, 95 were seropositive (67.4%) and 46 seronegative (32.6%) under the 8-antigen panel. The 'global' model achieved an AUC of 0.81, with 83.3% specificity and 69.5% sensitivity for infections within nine months, increasing to 82% sensitivity for last-month infections. In the cross-sectional study, serology identified more positives than PCR, reflecting detection of exposure not captured by PCR. This study provides the first validation of serological markers of <i>P. vivax</i> exposure in Cambodia, showing that such tools can identify recent and asymptomatic infections, though sensitivity was below target. Serology-based surveillance and strategies such as <i>Pv</i>SeroTAT could accelerate malaria elimination. NIH/NIAID, ICEMR Asia-Pacific U19AI129392.