Malaria transmission in Myanmar has declined dramatically over the past decade (by as much as 90% since 2005 in some provinces1), and is expected to continue on this trajectory as the Greater Mekong Subregion strives for malaria elimination by the year 2030. These rapid declines in malaria transmission and thus, exposure, may lead to declines in population levels of protective antimalarial immunity. The objective of this study was to longitudinally observe changes in antimalarial immunity in a region that has recently achieved a marked decline in malaria transmission.
From April 2015 to June 2016 we performed a longitudinal study of 114 villages in the south-eastern states of Myanmar. Village health volunteers performed RDTs and collected 14,941 dried blood samples for analysis of antimalarial IgG by ELISA and infection by qPCR. Malaria prevalence by RDT was extremely low (0.14% over the entire study), however when measured by qPCR prevalence of P.falciparum or P.vivax infection was 5% at the end of the 2015 high transmission season. Despite a low prevalence of infection, high levels of IgG specific for P.falciparum and P.vivax merozoite antigen AMA1 were observed. Multilevel mixed-effects modelling revealed that PfAMA1 IgG rose significantly during high transmission season, followed by a gradual decline, and that PvAMA1 declined over the course of the study. Despite these eventual declines, seroprevalence of Pf and PvAMA1 IgG remained over 30% and 20% at the conclusion of the study, respectively.
Despite recent large-scale reductions in malaria incidence, high levels of antimalarial antibodies are being maintained in this pre-elimination setting. The maintenance of antimalarial IgG in low transmission settings is likely influence ongoing malaria transmission, highlighting the importance of understanding the role of immunity in the epidemiology of malaria as we strive for elimination in the Greater Mekong Subregion.