High chloroquine treatment failure rates and predominance of mutant genotypes associated with chloroquine and antifolate resistance among falciparum malaria patients from the island of Car Nicobar, India.

Objectives: An in vivo chloroquine efficacy study was undertaken on the island of Car Nicobar because a temporal rise in the Plasmodium falciparum parasite population containing mutations in the chloroquine resistance transporter (PfCRT) protein has been reported there.

Methods: A WHO protocol with a 28 day follow-up schedule was used for chloroquine efficacy studies. Finger-prick blood from P. falciparum malaria patients was used for sequencing the genes encoding PfCRT (exon 2), dihydrofolate reductase (PfDHFR) and dihydropteroate synthetase (PfDHPS).

Results: The majority of patients showed chloroquine treatment failure (60.42%, n=48). A higher early treatment failure (ETF) rate was recorded among non-responders (23 of 29, 79.31%). Each patient, irrespective of their chloroquine response, was infected with P. falciparum that contained mutated PfCRT (predominantly genotype C72V73I74E75T76) associated with high chloroquine resistance and none with the wild-type pfcrt gene. Therefore, mutated PfCRT was also present in the P. falciparum isolates of all the chloroquine responders. The majority of individuals from both groups also contained parasites with a high number of two-locus PfDHFR-PfDHPS mutations, associated with a high level of antifolate resistance.

Conclusions: There is a predominance of chloroquine- and antifolate-resistant P. falciparum malaria in Car Nicobar, requiring an alternative antimalarial drug treatment policy, such as implementation of artesunate combination therapy (ACT), for this island.