Molecular surveillance of drug-resistant malaria in India

Drug-resistant Plasmodium falciparum parasite poses a great problem for the malaria control programme of any country. The most commonly used antimalarial drugs, viz. chloroquine (CQ) and sulphadoxine-pyrimethamine (SP) have been rendered ineffective and are replaced by the artesunate-based combination therapy (ACT). In India, artesunate is combined with SP (ASP). Nevertheless, CQ is continued to be used. Therefore, Indian P. falciparum population continues to be under CQ and SP pressure. Molecular surveillance should be used to keep track of the drug-resistant parasite population in the field for better implementation of the drug policy. By employing molecular markers, we have generated a large body of data on the status of CQ and SP resistance-associated mutations in Indian P. falciparum population. These data revealed a regional variation in the frequency of the parasite with mutant allele of the selected drug resistance marker. The mutations in these markers were found to be fixed in the parasite population as the microsatellites flanking the mutant alleles showed reduced genetic variation. However, the selection valley of the reduced genetic variation in these flanking microsatellites was narrower for the Indian isolates than that reported for the African or South East Asian population, thereby indicating a lower selection pressure on Indian parasite population. The origin of the drug-resistant parasite in India seems to be from South East Asia. Increased parasite population with higher number of mutations associated with antifolate resistance should be a cause of concern as ACT in India has the SP component.