Applying novel Plasmodium vivax serological exposure markers to quantify residual malaria transmission in the Philippines through repeated health facility surveys: the SMaRT study protocol

Background After decades of progress towards malaria elimination, Plasmodium vivax is now the predominant source of infection and the major obstacle towards elimination in the Asia-Pacific region. In the Philippines, the situation is slightly different with P. falciparum still accounting for the largest burden. However, there has been a steady increase in the total number of reported P. vivax cases in the main transmission hotspot of Palawan, as well as two years of consecutive outbreaks of P. vivax in the near-elimination setting of Sultan Kudarat. Here, we describe the protocol for a new study in Sultan Kudarat that aims to identify whether an underlying, hidden, burden of P. vivax contributes to the ongoing risk of outbreaks. Methods A challenge for surveillance of P. vivax is the presence of an additional hidden liver-stage, where parasites (hypnozoites) lie dormant for weeks to months before causing a relapse of infection. Hypnozoites cannot be detected with commercial diagnostic tests. We have designed novel serological exposure markers of recent P. vivax infection, which indirectly inform on hypnozoite carriage. In this study we will conduct a prospective 18-month survey in health facilities within Kalamansig, Sultan Kudarat, and compare epidemiology and serological data with that in archival samples from Palawan. We will enroll both care-seeking individuals and their companions, and utilise remote geolocation to uncover spatial trends. Discussion This study will generate important data for the malaria control program in the Philippines whilst also demonstrating utility of P. vivax serological exposure markers in near-elimination settings. We will utilise this data to build a decision-making framework to support novel, evidence-based elimination strategies relevant for the Philippines and the wider Asia-Pacific region.