Population genetics of changing Plasmodium vivax transmission in two endemic areas of Papua New Guinea
Plasmodium vivax is the most widely distributed human malaria parasite outside sub-Saharan Africa and causes significant morbidity. Global efforts to control and eventually to eliminate malaria have been less effective for P. vivax relative to P. falciparum due to its unique biology, including dormant liver stages that cause later relapse, and earlier commitment to transmission stages. Measuring changes in parasite population genetic structure is important to assess the impact of control on transmission dynamics, and to guide further control and elimination strategies. After the nationwide distribution of long lasting insecticide treated nets (LLIN) in Papua New Guinea (PNG), P. vivax prevalence initially reduced to low prevalence, but again resurged to near baseline levels. To explore changes in P. vivax population genetic parameters and identify sources of resurgence over this period, we applied a previously validated SNP barcode to genotype 376 P. vivax isolates obtained from serial cross-sectional surveys conducted over a decade in East Sepik (2005, 2012, 2016) and Madang (2006, 2010, 2014) Provinces. Population genetic analyses of the resulting parasite genotypes revealed contrasting spatiotemporal patterns. In Madang there was a strong bottleneck and near complete recovery of the population following resurgence, while in East Sepik, there was lower baseline complexity of infection and genetic diversity, a less dramatic impact on the parasite population after transmission decline, and expansion of multiple residual lineages upon resurgence. P. vivax decline was also accompanied by an increase in genetic differentiation between areas, with increasing parasite migration between areas with resurgence. The earlier implementation of LLIN in East Sepik may have contributed to these differing patterns, suggesting that long term sustained control efforts are essential to make a lasting impact on the P. vivax population.