Surveillance of artemisinin resistance in Plasmodium falciparum in India using the kelch13 molecular marker

Artemisinin-Resistant Plasmodium falciparum Malaria

For more than five decades, Southeast Asia (SEA) has been fertile ground for the emergence of drug-resistant Plasmodium falciparum malaria. After generating parasites resistant to chloroquine, sulfadoxine, pyrimethamine, quinine, and mefloquine, this region has now spawned parasites resistant to artemisinins, the world's most potent antimalarial drugs. In areas where artemisinin resistance is prevalent, artemisinin combination therapies (ACTs)-the first-line treatments for malaria-are failing fast. This worrisome development threatens to make malaria practically untreatable in SEA, and threatens to compromise global endeavors to eliminate this disease. A recent series of clinical, in vitro, genomics, and transcriptomics studies in SEA have defined in vivo and in vitro phenotypes of artemisinin resistance, identified its causal genetic determinant, explored its molecular mechanism, and assessed its clinical impact. Specifically, these studies have established that artemisinin resistance manifests as slow parasite clearance in patients and increased survival of early-ring-stage parasites in vitro; is caused by single nucleotide polymorphisms in the parasite's K13 gene, is associated with an upregulated "unfolded protein response" pathway that may antagonize the pro-oxidant activity of artemisinins, and selects for partner drug resistance that rapidly leads to ACT failures. In SEA, clinical studies are urgently needed to monitor ACT efficacy where K13 mutations are prevalent, test whether new combinations of currently available drugs cure ACT failures, and advance new antimalarial compounds through preclinical pipelines and into clinical trials. Intensifying these efforts should help to forestall the spread of artemisinin and partner drug resistance from SEA to sub-Saharan Africa, where the world's malaria transmission, morbidity, and mortality rates are highest.

A Method for Amplicon Deep Sequencing of Drug Resistance Genes in Plasmodium falciparum Clinical Isolates from India

A major challenge to global malaria control and elimination is early detection and containment of emerging drug resistance. Next-generation sequencing (NGS) methods provide the resolution, scalability, and sensitivity required for high-throughput surveillance of molecular markers of drug resistance. We have developed an amplicon sequencing method on the Ion Torrent PGM platform for targeted resequencing of a panel of six Plasmodium falciparum genes implicated in resistance to first-line antimalarial therapy, including artemisinin combination therapy, chloroquine, and sulfadoxine-pyrimethamine. The protocol was optimized using 12 geographically diverse P. falciparum reference strains and successfully applied to multiplexed sequencing of 16 clinical isolates from India. The sequencing results from the reference strains showed 100% concordance with previously reported drug resistance-associated mutations. Single-nucleotide polymorphisms (SNPs) in clinical isolates revealed a number of known resistance-associated mutations and other nonsynonymous mutations that have not been implicated in drug resistance. SNP positions containing multiple allelic variants were used to identify three clinical samples containing mixed genotypes indicative of multiclonal infections. The amplicon sequencing protocol has been designed for the benchtop Ion Torrent PGM platform and can be operated with minimal bioinformatics infrastructure, making it ideal for use in countries that are endemic for the disease to facilitate routine large-scale surveillance of the emergence of drug resistance and to ensure continued success of the malaria treatment policy.

No Polymorphism in Plasmodium falciparum K13 Propeller Gene in Clinical Isolates from Kolkata, India

Molecular markers associated with artemisinin resistance in Plasmodium falciparum are yet to be well defined. Recent studies showed that polymorphisms in K13 gene are associated with artemisinin resistance. The present study was designed to know the pattern of polymorphisms in propeller region of K13 gene among the clinical isolates collected from urban Kolkata after five years of ACT implementation. We collected 59 clinical isolates from urban Kolkata and sequenced propeller region of K13 gene in 51 isolates successfully. We did not find any mutation in any isolate. All patients responded to the ACT, a combination of artesunate + sulphadoxine-pyrimethamine. The drug regimen is still effective in the study area and there is no sign of emergence of resistance against artemisinin as evidenced by wild genotype of K13 gene in all isolates studied.

Observing in real time the evolution of artemisinin resistance in Plasmodium falciparum

Simple genetic changes that correlate with drug resistance are used routinely to identify resistant pathogens. These "molecular markers" have usually been defined long after the phenotype of resistance was noted. The molecular changes at the "end game" reflect a long and complex evolution of genetic changes, but once a solidly resistant set of changes assembles under drug selection, that genotype is likely to become fixed, and resistant pathogens will spread widely. Artemisinins are currently used worldwide to treat malaria caused by Plasmodium falciparum, but parasite response has diminished rapidly in the Mekong region of Southeast Asia. Should artemisinins lose potency completely and this effect spread worldwide, effective malaria treatment would be almost impossible. The full range of modern methods has been applied to define rapidly the genetic changes responsible. Changes associated with artemisinin resistance are complex and seem to be evolving rapidly, especially in Southeast Asia. This is a rare chance to observe the early stages in evolution of resistance, and to develop strategies to reverse or mitigate the trend and to protect these key medicines.

Mosquito-borne diseases in Assam, north-east India: current status and key challenges

Mosquito-borne diseases, including malaria, Japanese encephalitis (JE), lymphatic filariasis and dengue, are major public health concerns in the north-eastern state of Assam, deterring equitable socioeconomic and industrial development. Among these, malaria and JE are the predominant infections and are spread across the state. The incidence of malaria is, however, gradually receding, with a consistent decline in cases over the past few years, although entry and spread of artemisinin-resistant Plasmodium falciparum remains a real threat in the country. JE, formerly endemic in upper Assam, is currently spreading fast across the state, with confirmed cases and a high case-fatality rate affecting all ages. Lymphatic filariasisis is prevalent but its distribution is confined to a few districts and disease transmission is steadily declining. Dengue has recently invaded the state, with a large concentration of cases in Guwahati city that are spreading to suburban areas. Control of these diseases requires robust disease surveillance and integrated vector management on a sustained basis, ensuring universal coverage of evidence-based key interventions based on sound epidemiological data. This paper aims to present a comprehensive review of the status of vector-borne diseases in Assam and to address the key challenges.