Background. Papua province has the highest burden of malaria in Indonesia, with both drug-resistant P. vivax and P. falciparum prevalent. As a consequence of the declining efficacy of chloroquine in the region, Papua-Indonesia became one of the first regions to implement a unified artemisinin-based combination therapy (ACT) policy of dihydroartemisinin-piperaquine for all species of malaria in March 2006. The current study characterizes longitudinal changes in the genetic diversity and population structure of co-endemic P. vivax and P. falciparum populations in Papua, with a particular focus on the period before and after ACT implementation.
Methods. The study was conducted in Mimika District, in southern Papua Province. Microsatellite typing was undertaken on randomly selected parasite isolates (231 P. falciparum and 225 P. vivax) collected between 2004 and 2006 (pre-ACT) and between 2011 and 2016 (post-ACT) from symptomatic patients with uncomplicated malaria.
Results. There was a significant decrease in the proportion of polyclonal P. vivax infections after ACT implementation (57% (43/75) to 33% (49/150); p=0.001), although there was no evidence of a reduction in genetic diversity or inbreeding events. The P. falciparum population demonstrated a decline in the proportion of polyclonal infections post-ACT from 18% (16/91) pre-ACT to 9% (13/139) post-ACT; p=0.104. There was evidence of increased inbreeding with a higher prevalence of identical infections post-ACT 46% (60/130) compared to 24% (21/89) pre-ACT; p=0.001.
Conclusions. There was evidence of a reduction in both P. falciparum and P. vivax transmission from the period 2004-6 to 2011-16. The change on P. falciparum was greater, as demonstrated by the degree of population bottlenecking relative to P. vivax. A number of factors may have contributed to the decline in local transmission, with the implementation of ACT likely playing a major role. Anti-relapse therapy is likely to be a key component to achieve further impact on P. vivax.