Genetic population of Plasmodium knowlesi during pre-malaria elimination in Thailand

Rungniran Sugaram,Patcharida Boondej,Prayuth Sudathip,Aungkana Saejeng,Watcharee Pagornrat,Usa Boonyuen,Arjen M Dondorp,Suttipat Srisutham,Chanon Kunasol,Mallika Imwong

doi:10.1186/s12936-021-03990-x

Abstract

BackgroundThailand is committed to eliminating malaria by 2024. From 2013 to 2020, the total number of malaria cases have decreased, from 37,741 to 4474 (an 88.1% reduction). However, infections with Plasmodium knowlesi, a monkey malarial pathogen that can also infect humans, have been increasingly observed. This study focused on the molecular analysis of P. knowlesi parasites causing malaria in Thailand.MethodsUnder Thailand’s integrated Drug Efficacy Surveillance (iDES), which includes drug-resistance monitoring as part of routine case-based surveillance and responses, specimens were collected from malaria patients (n = 966) between 2018 and 2020. Thirty-one mono P. knowlesi infections (3.1%), most of which were from eastern and southern Thailand, were observed and confirmed by nested PCR assay and DNA sequencing. To evaluate whether these pathogens were from different lineages, cluster analysis based on seven microsatellite genotyping markers and the merozoite surface protein 1 (pkmsp1) gene was carried out. The P. knowlesi pyrimethamine resistance gene dihydrofolate reductase (pkdhfr) was sequenced and homology modelling was constructed.ResultsThe results of analysing the seven microsatellite markers and pkmsp1 sequence demonstrated that P. knowlesi parasites from eastern Thailand were of the same lineage as those isolated in Cambodia, while the parasites causing malaria in southern Thailand were the same lineage as those isolated from Malaysia. The sequencing results for the pkdhfr genes indicated the presence of two mutations, Arg34Leu and a deletion at position 105. On analysis with homology modelling, the two mutations were not associated with anti-malarial drug resistance.ConclusionsThis report compared the genetic populations of P. knowlesi parasites in Thailand from 2018 to 2020 and have shown similar lineages as those isolated in Cambodia and Malaysia of P. knowlesi infection in Thailand and demonstrated that the P. knowlesi parasites were of the same lineages as those isolated in Cambodia and Malaysia. The parasites were also shown to be sensitive to pyrimethamine.

Highlights

Thailand is committed to eliminating malaria by 2024
Plasmodium knowlesi infection in Thailand Of the 966 malaria collected samples, 31 (3.2%) monoinfections with P. knowlesi were confirmed by nested Polymerase chain reaction (PCR) assay and Deoxyribonucleic acid (DNA) sequencing
Haplotype network analysis was performed with the microsatellite marker results (Fig. 2) and showed that P. knowlesi isolated from eastern parts of Thailand, including Surin, Chanthaburi, and Trat, were the same haplotype as P. knowlesi parasites isolated from Battambang, Cambodia

Summary

Introduction

Thailand is committed to eliminating malaria by 2024. From 2013 to 2020, the total number of malaria cases have decreased, from 37,741 to 4474 (an 88.1% reduction). Human malarial infection with this parasite was first reported in 1965 [4], and a second case presented in 1971 in Malaysia [5]. Plasmodium knowlesi infections have shown distribution across the Greater Mekong Subregion (GMS), and previous P. knowlesi infections in the GMS have been recorded in Malaysia [6,7,8,9], Thailand [10,11,12], Myanmar [13, 14], Laos [15, 16], Vietnam [17, 18], and Cambodia [19]. The distribution of P. knowlesi may obstruct the malaria elimination agendas of countries of the GMS of Southeast Asia, especially due to asymptomatic cases, which have been previously reported [20]

Methods

Results

Discussion

Conclusion