K13-propeller gene polymorphisms in Plasmodium falciparum parasite population: a systematic review protocol of burden and associated factors

Despite the currently reported emergence and spread of resistance to artemisinin agents, there are no known effective alternative medicines for malaria treatment in the pipeline. Malaria still remains the leading cause of morbidity and mortality among children under five especially in Sub-Saharan Africa and other malaria-endemic countries [1]. Delay in the discovery of an effective alternative treatment to malaria in case of widespread artemisinin resistance threatens malaria control, treatment, and elimination efforts globally and may further worsen the consequences of malaria disease globally [2, 3]. Furthermore, widespread resistance to artemisinin agents threatens malaria control and eradication efforts [3]. This therefore calls for efforts to track and reduce the risk of global spread or the independent emergence of artemisinin resistance in other malaria-endemic countries outside Southeast Asia [4].

Artemisinin agents are the cornerstone of malaria control and eradication efforts globally. The agents are used for both uncomplicated and complicated malaria. However, in Southeast Asia, decreased parasite sensitivity to artemisinin agents associated with polymorphisms in the parasite K13-propeller gene has been reported [5, 6]. The K13-propeller gene polymorphisms associated with decreased artemisinin parasite clearance reported in Southeast Asia include C580Y, R539T, R543I, and Y493H [6]. In areas outside Southeast Asia, K13-propeller gene polymorphisms different from those detected and validated in Cambodia have been reported [5]. This has hindered regular surveillance of artemisinin resistance among P. falciparum parasites in other malaria-endemic countries outside Southeast Asia. Although there has been no confirmed case of artemisinin resistance outside the Southeast, the likelihood of its emergence and spread still exists. However, currently, there are no efforts to establish the phenotypic effect of the different K13-gene polymorphisms reported outside Southeast Asia on P. falciparum parasite response to artemisinin exposure.

Artemisinin resistance surveillance is done using both phenotypic and genotypic methods. Parasite sensitivity analysis using RSA_0-3h is currently used to establish parasite clearance using artemisinin agents [7, 8]. However, due to restrictive cost, there are limited sentinel sites in malaria-endemic countries where these studies are performed and are not regularly done. WHO recommends complimenting resistance surveillance by using molecular markers, as they are relatively cheaper and easier to perform [1]. The lack of confirmed molecular markers of artemisinin resistance outside Southeast Asia however has limited resistance surveillance efforts in this countries especially Africa. In malaria-affected areas outside Southeast Asia, the existence of several non-validated K13-gene polymorphisms among Plasmodium falciparum parasites further complicates molecular surveillance.

Currently, different K13-polymorphisms are being reported outside Southeast Asia. This could be due to variations in environmental pressures [5]. Due to variations in the reported P. falciparum K13-gene polymorphisms, it is currently not clear what the dominant mutations in P. falciparum parasites outside Southeast Asia are. In addition, the mutations are different from those that have been validated and confirmed to be associated with reduced artemisinin clearance. There has been no systematic review done to date on the K13-propeller gene polymorphisms being reported among P. falciparum parasites in Africa and other malaria-endemic areas outside Southeast Asia. This systematic review is thus intended to collate evidence from published articles to establish the most prevalent K13-gene polymorphism (s) in P. falciparum parasites in Africa and other malaria-endemic countries outside Southeast Asia.

The systematic review protocol has been developed following the PRISMA-P 2015 statement [9], and this will be followed while reporting the findings of the review (Additional file 1). The review will be done following PECOS: population (P), Plasmodium falciparum parasites in countries affected by malaria, exposure (E), use of artemisinin agents in malaria treatment, comparator (C), none, outcome (O), K13-propeller gene polymorphisms occurring in P. falciparum parasites in countries affected by malaria, study design (S), the review will include articles from cross-sectional studies and those reporting using Plasmodium falciparum DNA samples collected on day zero (0) of clinical trial studies.

Artemisinin agents are an integral part of the current global efforts to control and eradicate malaria [12]. However, monitoring of resistance to these agents faces a challenge especially outside Southeast Asia due to the lack of validated molecular markers of resistance. This potentially limits the establishment of interventions to protect the efficacy of artemisinin agents [12]. Artemisinin and their derivatives are the only highly efficacious agents used currently in malaria treatment with no known alternatives [12]. This leaves malaria affected populations vulnerable to severe effects of the disease in case of widespread resistance as previously observed with chloroquine [13]. Currently, there have been reports of delayed parasite clearance by artemisinin agents in Southeast Asia, an indicator of potential emergence of resistance [6].

A study by Ariey et al [6] validated K13-propeller gene polymorphisms in Plasmodium falciparum parasites associated with delayed parasite clearance by artemisinin agents. Multiple studies have, however, failed to replicate identification of such molecular resistance against artemisinin agents outside Southeast Asia. In Africa, which bears the largest burden of malaria, molecular markers of artemisinin resistance have not yet been confirmed. In addition, multiple studies report K13-propeller gene polymorphisms different from those validated for causing artemisinin resistance in Southeast Asia. Thus, there is a lack of information on the role several reported K13-gene polymorphisms in malaria-endemic countries outside Southeast Asia play in artemisinin resistance. To help guide molecular artemisinin resistance surveillance outside Southeast Asia, there is a need to establish the most frequently reported K13-gene polymorphisms. In addition, validation of the role reported K13-gene polymorphisms play in parasite artemisinin resistance is urgently needed.

The current review seeks to collate evidence on K13-gene polymorphisms commonly reported in different malaria-endemic regions of the world. This will help guide in prioritizing selection of K13-gene polymorphisms outside Southeast Asia whose role in causing Plasmodium falciparum artemisinin resistance needs to be established. Although therapeutic efficacy studies are considered the gold standard for establishing artemisinin resistance [14], WHO recommends that therapeutic efficacy studies be supplemented by surveillance of molecular markers of resistance [15]. This is currently not possible outside Southeast Asia due to the lack of validated K13-gene polymorphisms.