Therapeutic efficacy of chloroquine and sequence variation in pfcrt gene among patients with falciparum malaria in central India

Abstract

Objectives: To assess the therapeutic efficacy of chloroquine (CQ) treatment against uncomplicated Plasmodium falciparum infections in a tribal population of central India (Madhya Pradesh) and to investigate the prevalence of mutant P. falciparum chloroquine-resistant transporter (pfcrt) gene in the parasite population. Methods: Clinical and parasitological response was determined by in-vivo testing. For molecular testing, the parasite DNA was extracted from blood samples and used to amplify and sequence parts of the pfcrt (44-177 codons), MSP1 (block 2) and MSP2 (central repeat region) genes. Results: Of 463 patients presenting fever, 137 tested positive for P. falciparum. They were treated with CQ. Of these, 58% participated in the study. Overall, treatment failure occurred in 53% of participants. Children under 5 years of age showed significantly more CQ resistance than adults. Mutant genotype S₇₂V₇₃M₇₄N₇₅T₇₆ was prevalent among both CQ responders (61.29%) and non-responders (66.7%). Interestingly, several patients from the CQ non-responder group (33.3%, n=39) were harbouring parasite with wild type C₇₂V₇₃M₇₄N₇₅K₇₆ genotype of the pfcrt gene. Microsatellite sequences downstream of exon 2 varied widely among both wild type and mutant pfcrt haplotypes. Conclusion: The high rate of treatment failure in the present study clearly indicates the need to reassess the use of CQ as first-line antimalarial therapy in central India. This is supported by the presence of mutant pfcrt genotype among majority of the parasite population of the CQ non-responder group of patients. However, the presence of wild type amino acid at codon 76 of the pfcrt gene among several patients with CQ non-responders requires further investigations.