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Stanley P, Rajkumari N, Sivaradjy M. Molecular detection of antimalarial resistance in Plasmodium vivax isolates from a tertiary care setting in Puducherry. Indian J Med Microbiol 2024; 47:100496. [PMID: 37949233 DOI: 10.1016/j.ijmmb.2023.100496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Revised: 09/14/2023] [Accepted: 10/18/2023] [Indexed: 11/12/2023]
Abstract
PURPOSE The study was aimed at detecting the mutation patterns in the drug targets in Plasmodium vivax that confer resistance to the common antimalarial agents used in India. METHODS A total of 27 Plasmodium vivax isolates collected from whole blood samples over a three year period were subjected to PCR amplification followed by sequencing of the genes pvmdr1, pvdhfr, pvdhps and pvk12, which serve as the molecular targets to detect resistance to chloroquine, pyrimethamine, sulfadoxine and artemisinin respectively. RESULTS The study found T958 M F1076L double mutants of pvmdr1 in 52 %(14/27) isolates, S58R S117 N double mutants of pvdhfr in 67 % (18/27) isolates, A383G A553G double mutant pvdhps in 59 % (16/27) isolates and wild type of pvk12 gene in all the isolates. CONCLUSIONS There was a rise in the proportion of double mutants of pvmdr1 and pvdhfr over time. Those cases with double mutant pvmdr1 gene in their isolates were found to have a prolonged hospital stay compared to those without, indicating reduced clinical response to chloroquine.
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Affiliation(s)
- Pheba Stanley
- Department of Microbiology, Jawaharlal Institute of Postgraduate Medical Education and Research, Dhanvantri Nagar, Puducherry, 605006, India.
| | - Nonika Rajkumari
- Department of Microbiology, Jawaharlal Institute of Postgraduate Medical Education and Research, Dhanvantri Nagar, Puducherry, 605006, India.
| | - Monika Sivaradjy
- Department of Microbiology, Jawaharlal Institute of Postgraduate Medical Education and Research, Dhanvantri Nagar, Puducherry, 605006, India; Department of Microbiology, ESIC Medical College& PGIMSR, Chennai, 78, India.
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Kojom Foko LP, Narang G, Jakhan J, Tamang S, Moun A, Singh V. Nationwide spatiotemporal drug resistance genetic profiling from over three decades in Indian Plasmodium falciparum and Plasmodium vivax isolates. Malar J 2023; 22:236. [PMID: 37582796 PMCID: PMC10428610 DOI: 10.1186/s12936-023-04651-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Accepted: 07/18/2023] [Indexed: 08/17/2023] Open
Abstract
BACKGROUND Drug resistance is a serious impediment to efficient control and elimination of malaria in endemic areas. METHODS This study aimed at analysing the genetic profile of molecular drug resistance in Plasmodium falciparum and Plasmodium vivax parasites from India over a ~ 30-year period (1993-2019). Blood samples of P. falciparum and/or P. vivax-infected patients were collected from 14 regions across India. Plasmodial genome was extracted and used for PCR amplification and sequencing of drug resistance genes in P. falciparum (crt, dhps, dhfr, mdr1, k13) and P. vivax (crt-o, dhps, dhfr, mdr1, k12) field isolates. RESULTS The double mutant pfcrt SVMNT was highly predominant across the country over three decades, with restricted presence of triple mutant CVIET from Maharashtra in 2012. High rates of pfdhfr-pfdhps quadruple mutants were observed with marginal presence of "fully resistant" quintuple mutant ACIRNI-ISGEAA. Also, resistant pfdhfr and pfdhps haplotype has significantly increased in Delhi between 1994 and 2010. For pfmdr1, only 86Y and 184F mutations were present while no pfk13 mutations associated with artemisinin resistance were observed. Regarding P. vivax isolates, the pvcrt-o K10 "AAG" insertion was absent in all samples collected from Delhi in 2017. Pvdhps double mutant SGNAV was found only in Goa samples of year 2008 for the first time. The pvmdr1 908L, 958M and 1076L mutations were highly prevalent in Delhi and Haryana between 2015 and 2019 at complete fixation. One nonsynonymous novel pvk12 polymorphism was identified (K264R) in Goa. CONCLUSIONS These findings support continuous surveillance and characterization of P. falciparum and P. vivax populations as proxy for effectiveness of anti-malarial drugs in India, especially for independent emergence of artemisinin drug resistance as recently seen in Africa.
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Affiliation(s)
- Loick P Kojom Foko
- Parasite & Host Biology Group, ICMR-National Institute of Malaria Research, Dwarka, Sector 8, New Delhi, 110077, India
| | - Geetika Narang
- Parasite & Host Biology Group, ICMR-National Institute of Malaria Research, Dwarka, Sector 8, New Delhi, 110077, India
| | - Jahnvi Jakhan
- Parasite & Host Biology Group, ICMR-National Institute of Malaria Research, Dwarka, Sector 8, New Delhi, 110077, India
| | - Suman Tamang
- Parasite & Host Biology Group, ICMR-National Institute of Malaria Research, Dwarka, Sector 8, New Delhi, 110077, India
| | - Amit Moun
- Parasite & Host Biology Group, ICMR-National Institute of Malaria Research, Dwarka, Sector 8, New Delhi, 110077, India
| | - Vineeta Singh
- Parasite & Host Biology Group, ICMR-National Institute of Malaria Research, Dwarka, Sector 8, New Delhi, 110077, India.
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Lê HG, Naw H, Kang JM, Võ TC, Myint MK, Htun ZT, Lee J, Yoo WG, Kim TS, Shin HJ, Na BK. Molecular Profiles of Multiple Antimalarial Drug Resistance Markers in Plasmodium falciparum and Plasmodium vivax in the Mandalay Region, Myanmar. Microorganisms 2022; 10:2021. [PMID: 36296297 PMCID: PMC9612053 DOI: 10.3390/microorganisms10102021] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Revised: 10/05/2022] [Accepted: 10/08/2022] [Indexed: 09/21/2023] Open
Abstract
Emergence and spreading of antimalarial drug resistant malaria parasites are great hurdles to combating malaria. Although approaches to investigate antimalarial drug resistance status in Myanmar malaria parasites have been made, more expanded studies are necessary to understand the nationwide aspect of antimalarial drug resistance. In the present study, molecular epidemiological analysis for antimalarial drug resistance genes in Plasmodium falciparum and P. vivax from the Mandalay region of Myanmar was performed. Blood samples were collected from patients infected with P. falciparum and P. vivax in four townships around the Mandalay region, Myanmar in 2015. Partial regions flanking major mutations in 11 antimalarial drug resistance genes, including seven genes (pfdhfr, pfdhps, pfmdr-1, pfcrt, pfk13, pfubp-1, and pfcytb) of P. falciparum and four genes (pvdhfr, pvdhps, pvmdr-1, and pvk12) of P. vivax were amplified, sequenced, and overall mutation patterns in these genes were analyzed. Substantial levels of mutations conferring antimalarial drug resistance were detected in both P. falciparum and P. vivax isolated in Mandalay region of Myanmar. Mutations associated with sulfadoxine-pyrimethamine resistance were found in pfdhfr, pfdhps, pvdhfr, and pvdhps of Myanmar P. falciparum and P. vivax with very high frequencies up to 90%. High or moderate levels of mutations were detected in genes such as pfmdr-1, pfcrt, and pvmdr-1 associated with chloroquine resistance. Meanwhile, low frequency mutations or none were found in pfk13, pfubp-1, pfcytb, and pvk12 of the parasites. Overall molecular profiles for antimalarial drug resistance genes in malaria parasites in the Mandalay region suggest that parasite populations in the region have substantial levels of mutations conferring antimalarial drug resistance. Continuous monitoring of mutations linked with antimalarial drug resistance is necessary to provide useful information for policymakers to plan for proper antimalarial drug regimens to control and eliminate malaria in the country.
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Affiliation(s)
- Hương Giang Lê
- Department of Parasitology and Tropical Medicine, Institute of Health Sciences, Gyeongsang National University College of Medicine, Jinju 52727, Korea
- Department of Convergence Medical Science, Gyeongsang National University, Jinju 52727, Korea
| | - Haung Naw
- Department of Parasitology and Tropical Medicine, Institute of Health Sciences, Gyeongsang National University College of Medicine, Jinju 52727, Korea
- Department of Convergence Medical Science, Gyeongsang National University, Jinju 52727, Korea
| | - Jung-Mi Kang
- Department of Parasitology and Tropical Medicine, Institute of Health Sciences, Gyeongsang National University College of Medicine, Jinju 52727, Korea
- Department of Convergence Medical Science, Gyeongsang National University, Jinju 52727, Korea
| | - Tuấn Cường Võ
- Department of Parasitology and Tropical Medicine, Institute of Health Sciences, Gyeongsang National University College of Medicine, Jinju 52727, Korea
- Department of Convergence Medical Science, Gyeongsang National University, Jinju 52727, Korea
| | - Moe Kyaw Myint
- Department of Medical Research Pyin Oo Lwin Branch, Pyin Oo Lwin 05062, Myanmar
| | - Zaw Than Htun
- Department of Medical Research Pyin Oo Lwin Branch, Pyin Oo Lwin 05062, Myanmar
| | - Jinyoung Lee
- Department of Tropical Medicine, Inha Research Institute for Medical Sciences, Inha University College of Medicine, Incheon 22212, Korea
| | - Won Gi Yoo
- Department of Parasitology and Tropical Medicine, Institute of Health Sciences, Gyeongsang National University College of Medicine, Jinju 52727, Korea
- Department of Convergence Medical Science, Gyeongsang National University, Jinju 52727, Korea
| | - Tong-Soo Kim
- Department of Tropical Medicine, Inha Research Institute for Medical Sciences, Inha University College of Medicine, Incheon 22212, Korea
| | - Ho-Joon Shin
- Department of Microbiology, Ajou University College of Medicine, Suwon 16499, Korea
| | - Byoung-Kuk Na
- Department of Parasitology and Tropical Medicine, Institute of Health Sciences, Gyeongsang National University College of Medicine, Jinju 52727, Korea
- Department of Convergence Medical Science, Gyeongsang National University, Jinju 52727, Korea
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Polymorphisms of potential drug resistant molecular markers in Plasmodium vivax from China–Myanmar border during 2008‒2017. Infect Dis Poverty 2022; 11:43. [PMID: 35462549 PMCID: PMC9036727 DOI: 10.1186/s40249-022-00964-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 03/21/2022] [Indexed: 11/10/2022] Open
Abstract
Abstract
Background
Plasmodium vivax remains the predominant species at the China–Myanmar border, imposing a major challenge to the recent gains in regional malaria elimination. To closely supervise the emerging of drug resistance in this area, we surveyed the variations in genes potentially correlated with drug resistance in P. vivax parasite and the possible drug selection with time.
Methods
A total of 235 P. vivax samples were collected from patients suffering uncomplicated malaria at Yingjiang, Tengchong, and Longling counties, and Nabang port in China, Yunnan province, and Laiza sub-township in Myanmar, from 2008 to 2017. Five potential drug resistance genes were amplified utilizing nested-PCR and analyzed, including pvdhfr, pvdhps, pvmdr1, pvcrt-o, and pvk12. The Pearson’s Chi-squared test or Fisher’s exact test were applied to determine the statistical frequency differences of mutations between categorical data.
Results
The pvdhfr F57I/L, S58R, T61M and S117T/N presented in 40.6%, 56.7%, 40.1%, and 56.0% of the sequenced P. vivax isolates, and these mutations significantly decreased with years. The haplotype formed by these quadruple mutations predominated in Yingjiang, Tengchong, Longling and Nabang. While a mutation H99S/R (56.6%) dominated in Laiza and increased with time. In pvdhps, the A383G prevailed in 69.2% of the samples, which remained the most prevalent haplotype. However, a significant decrease of its occurrence was also noticed over the time. The S382A/C and A553G existed in 8.4% and 30.8% of the isolates, respectively. In pvmdr1, the mutation Y976F occurred at a low frequency in 5/232 (2.2%), while T958M was fixed and F1076L was approaching fixed (72.4%). The K10 insertion was detected at an occurrence of 33.2% in pvcrt-o, whereas there was no significant difference among the sites or over the time. No mutation was identified in pvk12.
Conclusions
Mutations related with resistance to antifolate drugs are prevalent in this area, while their frequencies decrease significantly with time, suggestive of increased susceptibility of P. vivax parasite to antifolate drugs. Resistance to chloroquine (CQ) is possibly emerging. However, since the molecular mechanisms underneath CQ resistance is yet to be better understood, close supervision of clinical drug efficiency and continuous function investigation is urgently needed to alarm drug resistance.
Graphical abstract
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Tang T, Xu Y, Cao L, Tian P, Shao J, Deng Y, Zhou H, Xiao B. Ten-Year Molecular Surveillance of Drug-Resistant Plasmodium spp. Isolated From the China-Myanmar Border. Front Cell Infect Microbiol 2021; 11:733788. [PMID: 34540721 PMCID: PMC8441003 DOI: 10.3389/fcimb.2021.733788] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Accepted: 08/09/2021] [Indexed: 11/13/2022] Open
Abstract
Antimalarial drug resistance has emerged as a major threat to global malaria control efforts, particularly in the Greater Mekong Subregion (GMS). In this study, we analyzed the polymorphism and prevalence of molecular markers associated with resistance to first-line antimalarial drugs, such as artemisinin, chloroquine, and pyrimethamine, using blood samples collected from malaria patients in the China-Myanmar border region of the GMS from 2008 to 2017, including 225 cases of Plasmodium falciparum and 194 cases of Plasmodium vivax. In artemisinin resistance, only the C580Y mutation with low frequency was detected in pfk13, and no highly frequent stable mutation was found in pvk12. In chloroquine resistance, the frequency of K76T mutation in pfcrt was always high, and the frequency of double mutations in pvmdr1 of P. vivax has been steadily increasing every year. In pyrimidine resistance, pfdhfr and pvdhfr had relatively more complex mutant types associated with drug resistance sites, and the overall mutation rate was still high. Therefore, artemisinin-based combination therapies are still suitable for use as the first choice of antimalarial strategy in the China-Myanmar border region in the future.
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Affiliation(s)
- Tongke Tang
- Institut Pasteur of Shanghai, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, China.,School of Life Science and Technology, ShanghaiTech University, Shanghai, China
| | - Yanchun Xu
- Yunnan Institute of Parasitic Diseases Control, Pu'er, China
| | - Long Cao
- CAS Key Laboratory of Molecular Virology and Immunology, Institut Pasteur of Shanghai, Chinese Academy of Sciences, Shanghai, China
| | - Penghai Tian
- CAS Key Laboratory of Molecular Virology and Immunology, Institut Pasteur of Shanghai, Chinese Academy of Sciences, Shanghai, China
| | - Jiang Shao
- Institutional Center for Shared Technologies and Facilities of Institut Pasteur of Shanghai, Chinese Academy of Sciences, Shanghai, China
| | - Yan Deng
- Yunnan Institute of Parasitic Diseases Control, Pu'er, China
| | - Hongning Zhou
- Yunnan Institute of Parasitic Diseases Control, Pu'er, China
| | - Bo Xiao
- CAS Key Laboratory of Molecular Virology and Immunology, Institut Pasteur of Shanghai, Chinese Academy of Sciences, Shanghai, China
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Jin X, Zhu S, Xu W, Chen J, Ruan W, Wang X. Limited polymorphism in k13 gene of Plasmodium falciparum and k12 of Plasmodium vivax isolates imported from African and Asian countries between 2014 and 2019 in Hangzhou city, China. BMC Infect Dis 2021; 21:853. [PMID: 34418991 PMCID: PMC8379771 DOI: 10.1186/s12879-021-06579-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 08/13/2021] [Indexed: 11/28/2022] Open
Abstract
Background Malaria causes major public health problems globally and drug resistance hinders its control and elimination. Molecular markers associated with drug resistance are considered as a beneficial tool to monitor the disease trends, evolution and distribution so as to help improve drug policy. Methods We collected 148 Plasmodium falciparum and 20 Plasmodium vivax isolates imported into Hangzhou city, China between 2014 and 2019. k13 gene of P. falciparum and k12 of P. vivax were sequenced. Polymorphisms and prevalence of k13 and k12 were analyzed. Results Most (98.65%, 146/148) P. falciparum infections were imported from Africa, and half P. vivax cases came from Africa and the other half from Asia. Nucleotide mutation prevalence was 2.03% (3/148) and the proportion of amino acid mutations was 0.68% (1/148). The amino acid mutation, A676S, was observed in an isolate from Nigeria. No mutation of k12 was observed from the parasites from African and Asian countries. Conclusions Limited polymorphism in k13 gene of P. falciparum isolates imported from African countries, but no evidence for the polymorphism of k12 in P. vivax samples from African and Asian countries was found. These results provide information for drug policy update in study region. Supplementary Information The online version contains supplementary material available at 10.1186/s12879-021-06579-6.
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Affiliation(s)
- Xingyi Jin
- Hangzhou Center for Disease Control and Prevention, Hangzhou, 310021, China
| | - Sujuan Zhu
- Hangzhou Center for Disease Control and Prevention, Hangzhou, 310021, China
| | - Weimin Xu
- Hangzhou Center for Disease Control and Prevention, Hangzhou, 310021, China
| | - Junfang Chen
- Hangzhou Center for Disease Control and Prevention, Hangzhou, 310021, China
| | - Wei Ruan
- Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou, 310051, China.
| | - Xiaoxiao Wang
- Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou, 310051, China.
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Buyon LE, Elsworth B, Duraisingh MT. The molecular basis of antimalarial drug resistance in Plasmodium vivax. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2021; 16:23-37. [PMID: 33957488 PMCID: PMC8113647 DOI: 10.1016/j.ijpddr.2021.04.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Revised: 03/31/2021] [Accepted: 04/08/2021] [Indexed: 01/07/2023]
Abstract
Plasmodium vivax is the most geographically widespread cause of human malaria and is responsible for the majority of cases outside of the African continent. While great progress has been made towards eliminating human malaria, drug resistant parasite strains pose a threat towards continued progress. Resistance has arisen to multiple antimalarials in P. vivax, including to chloroquine, which is currently the first line therapy for P. vivax in most regions. Despite its importance, an understanding of the molecular mechanisms of drug resistance in this species remains elusive, in large part due to the complex biology of P. vivax and the lack of in vitro culture. In this review, we will cover the extent and challenges of measuring clinical and in vitro drug resistance in P. vivax. We will consider the roles of candidate drug resistance genes. We will highlight the development of molecular approaches for studying P. vivax biology that provide the opportunity to validate the role of putative drug resistance mutations as well as identify novel mechanisms of drug resistance in this understudied parasite. Validated molecular determinants and markers of drug resistance are essential for the rapid and cost-effective monitoring of drug resistance in P. vivax, and will be useful for optimizing drug regimens and for informing drug policy in control and elimination settings. Drug resistance is emerging in Plasmodium vivax, an important cause of malaria. The complex biology of P. vivax and the limited range of research tools make it difficult to identify drug resistance. The molecular mechanisms of drug resistance in P. vivax remain elusive. This review highlights the extent of drug resistance, the putative mechanisms of resistance and new technologies for the study of P. vivax drug resistance.
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Affiliation(s)
- Lucas E Buyon
- Department of Immunology and Infectious Diseases, Harvard T. H. Chan School of Public Health, Boston, 02115, MA, USA
| | - Brendan Elsworth
- Department of Immunology and Infectious Diseases, Harvard T. H. Chan School of Public Health, Boston, 02115, MA, USA
| | - Manoj T Duraisingh
- Department of Immunology and Infectious Diseases, Harvard T. H. Chan School of Public Health, Boston, 02115, MA, USA.
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Mat Salleh NH, Rahman MFA, Samsusah S, De Silva JR, Ng DCE, Ghozali AH, Tan JH, Lai MY, Amir A, Liew JWK, Lau YL. Case report: recurrence of Plasmodium vivax malaria due to defective cytochrome P450 2D6 function in Pos Lenjang, Pahang, Malaysia. Trans R Soc Trop Med Hyg 2020; 114:700-703. [PMID: 32511702 DOI: 10.1093/trstmh/traa042] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Revised: 04/20/2020] [Accepted: 05/22/2020] [Indexed: 12/15/2022] Open
Abstract
Five children in Pos Lenjang, Pahang, Malaysia were PCR-positive for vivax malaria and were admitted to the hospital from 5 to 26 July 2019. One of the patients experienced three episodes of recurrence of vivax malaria. Microsatellite analysis showed that reinfection is unlikely. Drug resistance analysis indicated that Riamet (artemether-lumefantrine) is effective. Cytochrome P450 2D6 (CYP2D6) testing showed that this patient has defective CYP2D6 function. Primaquine failure to clear the Plasmodium vivax hypnozoites may be the cause of recurring infections in this patient. This report highlights the need for the development of liver-stage curative antimalarials that do not require metabolism by the CYP2D6 enzyme.
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Affiliation(s)
| | | | - Samsiah Samsusah
- Lipis District Health Office, 27200 Kuala Lipis, Pahang, Malaysia
| | - Jeremy Ryan De Silva
- Department of Parasitology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - David Chun-Ern Ng
- Department of Pediatrics, Hospital Tuanku Ja'afar, 70300 Seremban, Negeri Sembilan, Malaysia
| | | | - Jia Hui Tan
- Department of Parasitology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - Meng Yee Lai
- Department of Parasitology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - Amirah Amir
- Department of Parasitology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - Jonathan Wee Kent Liew
- Department of Parasitology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - Yee Ling Lau
- Department of Parasitology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
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Zhao Y, Wang L, Soe MT, Aung PL, Wei H, Liu Z, Ma T, Huang Y, Menezes LJ, Wang Q, Kyaw MP, Nyunt MH, Cui L, Cao Y. Molecular surveillance for drug resistance markers in Plasmodium vivax isolates from symptomatic and asymptomatic infections at the China-Myanmar border. Malar J 2020; 19:281. [PMID: 32758218 PMCID: PMC7409419 DOI: 10.1186/s12936-020-03354-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Accepted: 07/28/2020] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND In the Greater Mekong sub-region, Plasmodium vivax has become the predominant species and imposes a major challenge for regional malaria elimination. This study aimed to investigate the variations in genes potentially related to drug resistance in P. vivax populations from the China-Myanmar border area. In addition, this study also wanted to determine whether divergence existed between parasite populations associated with asymptomatic and acute infections. METHODS A total of 66 P. vivax isolates were obtained from patients with acute malaria who attended clinics at the Laiza area, Kachin State, Myanmar in 2015. In addition, 102 P. vivax isolates associated with asymptomatic infections were identified by screening of volunteers without signs or symptoms from surrounding villages. Slide-positive samples were verified with nested PCR detecting the 18S rRNA gene. Multiclonal infections were further excluded by genotyping at msp-3α and msp-3β genes. Parasite DNA from 60 symptomatic cases and 81 asymptomatic infections was used to amplify and sequence genes potentially associated with drug resistance, including pvmdr1, pvcrt-o, pvdhfr, pvdhps, and pvk12. RESULTS The pvmdr1 Y976F and F1076L mutations were present in 3/113 (2.7%) and 97/113 (85.5%) P. vivax isolates, respectively. The K10 insertion in pvcrt-o gene was found in 28.2% of the parasites. Four mutations in the two antifolate resistance genes reached relatively high levels of prevalence: pvdhfr S58R (53.4%), S117N/T (50.8%), pvdhps A383G (75.0%), and A553G (36.3%). Haplotypes with wild-type pvmdr1 (976Y/997K/1076F) and quadruple mutations in pvdhfr (13I/57L/58R/61M/99H/117T/173I) were significantly more prevalent in symptomatic than asymptomatic infections, whereas the pvmdr1 mutant haplotype 976Y/997K/1076L was significantly more prevalent in asymptomatic than symptomatic infections. In addition, quadruple mutations at codons 57, 58, 61 and 117 of pvdhfr and double mutations at codons 383 and 553 of pvdhps were found both in asymptomatic and symptomatic infections with similar frequencies. No mutations were found in the pvk12 gene. CONCLUSIONS Mutations in pvdhfr and pvdhps were prevalent in both symptomatic and asymptomatic P. vivax infections, suggestive of resistance to antifolate drugs. Asymptomatic carriers may act as a silent reservoir sustaining drug-resistant parasite transmission necessitating a rational strategy for malaria elimination in this region.
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Affiliation(s)
- Yan Zhao
- Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, 110122, Liaoning, China
| | - Lin Wang
- Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, 110122, Liaoning, China
| | - Myat Thu Soe
- Myanmar Health Network Organization, Yangon, Myanmar
| | | | - Haichao Wei
- Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, 110122, Liaoning, China
| | - Ziling Liu
- Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, 110122, Liaoning, China
| | - Tongyu Ma
- Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, 110122, Liaoning, China
| | - Yuanyuan Huang
- Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, 110122, Liaoning, China
| | - Lynette J Menezes
- Department of Internal Medicine, Morsani College of Medicine, University of South Florida, 3720 Spectrum Boulevard, Suite 304, Tampa, FL, 33612, USA
| | - Qinghui Wang
- Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, 110122, Liaoning, China
| | | | | | - Liwang Cui
- Department of Internal Medicine, Morsani College of Medicine, University of South Florida, 3720 Spectrum Boulevard, Suite 304, Tampa, FL, 33612, USA.
| | - Yaming Cao
- Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, 110122, Liaoning, China.
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Wang X, Ruan W, Zhou S, Feng X, Yan H, Huang F. Prevalence of molecular markers associated with drug resistance of Plasmodium vivax isolates in Western Yunnan Province, China. BMC Infect Dis 2020; 20:307. [PMID: 32334523 PMCID: PMC7183581 DOI: 10.1186/s12879-020-05032-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Accepted: 04/15/2020] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND Plasmodium vivax is the most widely distributed malaria parasite, and its drug resistance poses unique challenges to malaria elimination. The Greater Mekong Subregion (GMS) is known as the global epicenter of multidrug resistance. Surveillance of molecular markers associated with drug resistance in this area will help to inform drug policy. METHODS Dry blood spots from 58 patients out of 109 with P. vivax infection between 2017, December and 2019, March were obtained from Yingjiang County, Yunnan Province, along the China-Myanmar border. Pvdhfr, Pvdhps, Pvmdr1 and Pvcrt-o were amplified and sequenced to assess gene mutations. The polymorphism and prevalence of these molecular markers were analyzed. RESULTS Mutations in Pvdhfr at codons 57, 58, 61, 99 and 117 were detected in 27.59, 48.28, 27.59, 32.76 and 48.28% of the isolates, respectively. Single mutant haplotype (I13F57S58T61S99S117I173) was the most frequent (29.31%, 17/58), followed by double mutant haplotype (20.69%, 12/58). Of three types of tandem repeat variations of Pvdhfr, deletion type was the most common. Pvdhps showed a lower prevalence among mutation genotypes. Single mutant was dominant and accounted for 34.48% (20/58). Prevalence of Pvmdr1 mutations at codons 958 and 1076 were 100.00% and 84.48%, respectively. The proportion of double and single mutant types was 84.48% (49/58) and 15.52% (9/58), respectively. Eleven samples (18.97%, 11/58) showed K10 "AAG" insertion in chloroquine resistance transporter gene Pvcrt-o. CONCLUSIONS There was moderate diversity of molecular patterns of resistance markers of Pvdhfr, Pvdhps, Pvmdr1 and Pvcrt-o in imported P. vivax cases to Yingjiang county in Western Yunnan, along the China-Myanmar border. Prevalence and molecular pattern of candidate drug resistance markers Pvdhfr, Pvdhps, Pvmdr1 and Pvcrt-o were demonstrated in this current study, which would help to update drug policy.
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Affiliation(s)
- Xiaoxiao Wang
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory of Parasite and Vector Biology, MOH, and WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Shanghai, People’s Republic of China
- Zhejiang Provincial Center for Disease Control and Prevention, Zhejiang, People’s Republic of China
| | - Wei Ruan
- Zhejiang Provincial Center for Disease Control and Prevention, Zhejiang, People’s Republic of China
| | - Shuisen Zhou
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory of Parasite and Vector Biology, MOH, and WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Shanghai, People’s Republic of China
| | - Xinyu Feng
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory of Parasite and Vector Biology, MOH, and WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Shanghai, People’s Republic of China
| | - He Yan
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory of Parasite and Vector Biology, MOH, and WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Shanghai, People’s Republic of China
| | - Fang Huang
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory of Parasite and Vector Biology, MOH, and WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Shanghai, People’s Republic of China
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11
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Duanguppama J, Mathema VB, Tripura R, Day NPJ, Maxay M, Nguon C, von Seidlein L, Dhorda M, Peto TJ, Nosten F, White NJ, Dondorp AM, Imwong M. Polymorphisms in Pvkelch12 and gene amplification of Pvplasmepsin4 in Plasmodium vivax from Thailand, Lao PDR and Cambodia. Malar J 2019; 18:114. [PMID: 30940150 PMCID: PMC6444602 DOI: 10.1186/s12936-019-2749-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 03/26/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Mutations in Pfkelch13 and Pfplasmepsin2/3 gene amplification are well-established markers for artemisinin and piperaquine resistance in Plasmodium falciparum, a widespread problem in the Greater Mekong Subregion (GMS). The Plasmodium vivax parasite population has experienced varying drug pressure dependent on local drug policies. We investigated the correlation between drug pressure from artemisinins and piperaquine and mutations in the P. vivax orthologous genes Pvkelch12 and Pvplasmepsin4 (Pvpm4), as candidate resistance markers. METHODS Blood samples from 734 P. vivax patients were obtained from Thailand (n = 399), Lao PDR (n = 296) and Cambodia (n = 39) between 2007 and 2017. Pvkelch12 and Pvpm4 was amplified and sequenced to assess gene mutations. To assess PvPM4 gene amplification, a Taqman® Real-Time PCR method was developed and validated. Selection of non-synonymous mutations was assessed by its ratio with synonymous mutations (Ka/Ks ratios). Mutation rates were compared to the estimated local drug pressure. RESULTS Polymorphisms in Pvkelch12 were rare. Pvkelch12 mutations V552I, K151Q and M124I were observed in 1.0% (7/734) of P. vivax samples. V552I was the most common mutation with a frequency of 0.7% (5/734), most of which (4/5) observed in Ubon Ratchathani, Thailand. Polymorphisms in Pvpm4 were more common, with a frequency of 40.3% (123/305) in 305 samples from Thailand, Lao PDR and Cambodia, but this was not related to the estimated piperaquine drug pressure in these areas (Pearson's χ2 test, p = 0.50). Pvpm4 mutation V165I was most frequent in Tak, Thailand (40.2%, 43/107) followed by Pailin, Cambodia (43.5%, 37/85), Champasak, Lao PDR (40.4%, 23/57) and Ubon Ratchathani, Thailand (35.7%, 20/56). Pvpm4 amplification was not observed in 141 samples from Thailand and Cambodia. For both Pvkelch12 and Pvpm4, in all areas and at all time points, the Ka/Ks values were < 1, suggesting no purifying selection. CONCLUSIONS A novel real-time PCR-based method to assess P. vivax Pvpm4 gene amplification was developed. Drug pressure with artemisinins and piperaquine in the GMS was not clearly related to signatures of selection for mutations in the P. vivax orthologous resistance genes Pvkelch12 and Pvpm4 in areas under investigation. Current resistance of P. vivax to these drugs is unlikely and additional observations including analysis of associated clinical data from these regions could further clarify current findings.
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Affiliation(s)
- Jureeporn Duanguppama
- Department of Molecular Tropical Medicine and Genetics, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.,Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Vivek Bhakta Mathema
- Department of Molecular Tropical Medicine and Genetics, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Rupam Tripura
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Nicholas P J Day
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.,Centre for Tropical Medicine, Churchill Hospital, Oxford, UK
| | - Mayfong Maxay
- Lao-Oxford-Mahosot Hospital-Wellcome Trust Research Unit, Mahosot Hospital, Vientiane, Lao People's Democratic Republic.,Institute of Research and Education Development, University of Health Sciences, Vientiane, Lao People's Democratic Republic
| | - Chea Nguon
- National Centre for Parasitology, Entomology & Malaria Control, Ministry of Health, Phnom Penh, Cambodia
| | - Lorenz von Seidlein
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Mehul Dhorda
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Thomas J Peto
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Francois Nosten
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.,Centre for Tropical Medicine, Churchill Hospital, Oxford, UK.,Shoklo Malaria Research Unit, Mae Sot, Faculty of Tropical Medicine, Mahidol University, Mae Sot, Thailand
| | - Nicholas J White
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.,Centre for Tropical Medicine, Churchill Hospital, Oxford, UK
| | - Arjen M Dondorp
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.,Centre for Tropical Medicine, Churchill Hospital, Oxford, UK
| | - Mallika Imwong
- Department of Molecular Tropical Medicine and Genetics, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand. .,Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
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Assessment of drug resistance associated genetic diversity in Mauritanian isolates of Plasmodium vivax reveals limited polymorphism. Malar J 2018; 17:416. [PMID: 30409138 PMCID: PMC6225721 DOI: 10.1186/s12936-018-2548-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Accepted: 10/24/2018] [Indexed: 01/09/2023] Open
Abstract
Background Plasmodium vivax is the predominant malaria species in northern Mauritania. Molecular data on P. vivax isolates circulating in West Africa are scarce. The present study analysed molecular markers associated with resistance to antifolates (Pvdhfr and Pvdhps), chloroquine (Pvmdr1), and artemisinin (Pvk12) in P. vivax isolates collected in two cities located in the Saharan zone of Mauritania. Methods Blood samples were obtained from P. vivax-infected patients recruited for chloroquine therapeutic efficacy study in 2013 and febrile patients spontaneously consulting health facilities in Nouakchott and Atar in 2015–2016. Fragments of Pvdhfr (codons 13, 33, 57, 58, 61, 117, and 174), Pvdhps (codons 382, 383, 512, 553, and 585), Pvmdr1 (codons 976 and 1076) and Pvk12 (codon 552) genes were amplified by PCR and sequenced. Results Most of the isolates in Nouakchott (126/154, 81.8%) and Atar (44/45, 97.8%) carried the wild-type Pvdhfr allelic variant (IPFSTSI). In Nouakchott, all mutants (28/154; 18.2%) had double Pvdhfr mutations in positions 58 and 61 (allelic variant IPFRMSI), whereas in Atar only 1 isolate was mutant (S117N, allelic variant IPFSTNI). The wild-type Pvdhps allelic variant (SAKAV) was found in all tested isolates (Nouakchott, n = 93; Atar, n = 37). Few isolates in Nouakchott (5/115, 4.3%) and Atar (3/79, 3.8%) had the mutant Pvmdr1 allele 976F or 1076L, but not both, including in pre-treatment isolates obtained from patients treated successfully with chloroquine. All isolates (59 in Nouakchott and 48 in Atar) carried the wild-type V552 allele in Pvk12. Conclusions Polymorphisms in Pvdhfr, Pvdhps, Pvmdr1, and Pvk12 were limited in P. vivax isolates collected recently in Nouakchott and Atar. Compared to the isolates collected in Nouakchott in 2007–2009, there was no evidence for selection of mutants. The presence of one, but not both, of the two potential markers of chloroquine resistance in Pvmdr1 in pre-treatment isolates did not influence the clinical outcome, putting into question the role of Pvmdr1 mutant alleles 976F and 1076L in treatment failure. Molecular surveillance is an important component of P. vivax malaria control programme in the Saharan zone of Mauritania to predict possible emergence of drug-resistant parasites.
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Tantiamornkul K, Pumpaibool T, Piriyapongsa J, Culleton R, Lek-Uthai U. The prevalence of molecular markers of drug resistance in Plasmodium vivax from the border regions of Thailand in 2008 and 2014. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2018; 8:229-237. [PMID: 29677637 PMCID: PMC6039358 DOI: 10.1016/j.ijpddr.2018.04.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 04/09/2018] [Accepted: 04/11/2018] [Indexed: 02/08/2023]
Abstract
The prevalence of Plasmodium vivax is increasing in the border regions of Thailand; one potential problem confounding the control of malaria in these regions is the emergence and spread of drug resistance. The aim of this study was to determine the genetic diversity in genes potentially linked to drug resistance in P. vivax parasites isolated from four different border regions of Thailand; Thai-Myanmar (Tak, Mae Hong Son and Prachuap Khiri Khan Provinces), and Thai-Cambodian borders (Chanthaburi Province). Isolates were collected from 345 P. vivax patients in 2008 and 2014, and parasite DNA extracted and subjected to nucleotide sequencing at five putative drug-resistance loci (Pvdhfr, Pvdhps, Pvmdr1, Pvcrt-o and Pvk12). The prevalence of mutations in Pvdhfr, Pvdhps and Pvmdr1 were markedly different between the Thai-Myanmar and Thai-Cambodian border areas and also varied between sampling times. All isolates carried the Pvdhfr (58R and 117N/T) mutation, however, whereas the quadruple mutant allele (I57R58M61T117) was the most prevalent (69.6%) in the Thai-Myanmar border region, the double mutant allele (F57R58T61N117) was at fixation on the Thai-Cambodian border (100%). The most prevalent genotypes of Pvdhps and Pvmdr1 were the double mutant (S382G383K512G553) (65.1%) and single mutant (M958Y976F1076) (46.5%) alleles, respectively on the Thai-Myanmar border while the single Pvdhps mutant (S382G383K512A553) (52.7%) and the triple Pvmdr1 mutant (M958F976L1076) (81%) alleles were dominant on the Thai-Cambodian border. No mutations were observed in the Pvcrt-o gene in either region. Novel mutations in the Pvk12 gene, the P. vivax orthologue of PfK13, linked to artemisinin resistance in Plasmodium falciparum, were observed with three nonsynonymous and three synonymous mutations in six isolates (3.3%).
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Affiliation(s)
- Kritpaphat Tantiamornkul
- Department of Parasitology and Entomology, Faculty of Public Health, Mahidol University, Rajvithi Rd, Rajthewee District, Bangkok 10400, Thailand; Faculty of Graduate Studies, Mahidol University, Phuttamonthon 4 Rd, Nakorn Pathom 73170, Thailand
| | - Tepanata Pumpaibool
- College of Public Health Science, Chulalongkorn University, Phyathai Rd, Bangkok 10330, Thailand
| | - Jittima Piriyapongsa
- Genome Technology Research Unit, National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Pathumthani 12120, Thailand
| | - Richard Culleton
- Malaria Unit, Department of Pathology, Institute of Tropical Medicine, Nagasaki University, Sakamoto, Nagasaki 8528523, Japan.
| | - Usa Lek-Uthai
- Department of Parasitology and Entomology, Faculty of Public Health, Mahidol University, Rajvithi Rd, Rajthewee District, Bangkok 10400, Thailand.
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Mbenda HGN, Zeng W, Bai Y, Siddiqui FA, Yang Z, Cui L. Genetic diversity of the Plasmodium vivax phosphatidylinositol 3-kinase gene in two regions of the China-Myanmar border. INFECTION GENETICS AND EVOLUTION 2018; 61:45-52. [PMID: 29462718 DOI: 10.1016/j.meegid.2018.02.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Revised: 02/12/2018] [Accepted: 02/14/2018] [Indexed: 12/25/2022]
Abstract
Artemisinin resistance in Plasmodium falciparum was associated with mutations in the propeller domain of the PfK13 gene and increased phosphatidylinositol-3'-kinase (PfPI3K) activity. Assessment of the genetic diversity of the PfK13 ortholog PvK12 in Plasmodium vivax field samples from the same hotspots of P. falciparum artemisinin resistance revealed a limited genetic diversity of PvK12. Following the same logic, we analyzed genetic variations of the PvPI3K gene in 188 P. vivax field isolates from two geographic locations along the China-Myanmar border. Overall, high genetic diversity of PvPI3K was observed; parasites from Yunnan's Tengchong County had higher genetic diversity than those from Laiza Township, Kachin State, Myanmar. Almost all the neutrality tests applied detected statistically significant deviation from zero. The negative Tajima's D values in both populations implicated that PvPI3K gene might have experienced either a directional selection or an expansion in population size. There was low linkage disequilibrium between the PvPI3K mutations in both populations, suggesting the existence of large, almost panmictic, parasite populations that enabled effective recombination. This later result was confirmed by the detection of a minimum of five recombination events in each population with two major breakpoints. Multiple tests for selection confirmed a signature of purifying selection on PvPI3K. All the amino acid mutations were predicted to be neutral for the PI3K protein's function. These findings provide insights on the genetic diversity of P. vivax populations along the China-Myanmar border.
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Affiliation(s)
| | - Weilin Zeng
- Department of Pathogen Biology and Immunology, Kunming Medical University, Kunming, China
| | - Yao Bai
- Department of Pathogen Biology and Immunology, Kunming Medical University, Kunming, China
| | - Faiza Amber Siddiqui
- Department of Entomology, Pennsylvania State University, 501 ASI Building, University Park, PA 16802, USA
| | - Zhaoqing Yang
- Department of Pathogen Biology and Immunology, Kunming Medical University, Kunming, China.
| | - Liwang Cui
- Department of Entomology, Pennsylvania State University, 501 ASI Building, University Park, PA 16802, USA.
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Abstract
The two main species causing malaria in humans, Plasmodium falciparum and P. vivax, differ significantly from each other in their evolutionary response to common drugs, but the reasons for this are not clear. Here we utilized the recently available large-scale genome sequencing data from these parasites and compared the pattern of single nucleotide polymorphisms, which may be related to these differences. We found that there was a five-fold higher preference for AT nucleotides compared to GC nucleotides at synonymous single nucleotide polymorphism sites in P. vivax. The preference for AT nucleotides was also present at non-synonymous sites, which lead to amino acid changes favouring those with codons of higher AT content. The substitution bias was also present at low and moderately conserved amino acid positions, but not at highly conserved positions. No marked bias was found at synonymous and non-synonymous sites in P. falciparum. The difference in the substitution bias between P. falciparum and P. vivax found in the present study may possibly contribute to their divergent evolutionary response to similar drug pressures.
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