Low Prevalence of Antimalarial Resistance Mutations in India During 2014-2015: Impact of Combining First-line Therapy With Primaquine

Antimalarial drug resistance surveillance and containment are crucial for countries aiming to eliminate malaria. Monitoring resistance evolution through studies before and after treatment policy changes is essential. A total of 939 Plasmodium falciparum-positive blood samples were collected between 2014 and 2015 across 10 sites in India, categorized into 4 geographic clusters. Polymerase chain reaction-amplified products were sequenced to identify point mutations at drug resistance-conferring genes (Pfdhfr, Pfdhps, Pfmdr1, and Pfk13). Triple Pfdhfr mutants were found only in northeast India bordering Myanmar, while the wild type (WT) was dominant in central India. Pfdhps WTs were prevalent in all areas, and no double mutants were found. Except in northwest India, Pfmdr1 WT was dominant in all clusters. Nonsynonymous double mutations were only found in northwest India. Only synonymous mutations occurred in Pfk13. These were found in central India at a low frequency. The pattern of linkage disequilibrium and principal component analysis reflects low pressure for drug resistance and heterogeneity between the geographic clusters. Resistance levels were highest in northeast India, close to the Myanmar border, where resistance is common. Primaquine has been widely used as a gametocidal and schizonticidal drug, likely contributing to maintaining low drug resistance levels and preventing strong selection for resistance.