2014-11-26-世界卫生组织-Minutes_of_the_Expert_Review_Committee_on_K13_molecular_marker_of_artemisinin_resistance_23页_301kb

Summary of the Expert Review Committee on K13 Molecular Marker of Artemisinin Resistance (15-16 September 2014)

Core Content

The Expert Review Committee (ERG) on K13 molecular marker of artemisinin resistance convened to evaluate the scientific evidence and public health potential of K13 mutations as indicators of artemisinin resistance in Plasmodium falciparum. The meeting emphasized the importance of integrating molecular markers into malaria control and elimination strategies, particularly in the context of artemisinin-based combination therapies (ACTs).

Main Points

• Molecular Markers and Policy: Molecular markers, such as K13, have been underutilized in guiding malaria policy. There is a need to simplify messages for malaria control programs and distinguish between research priorities and public health recommendations.

• K13 Mutations and Artemisinin Resistance:

  • K13 mutations are associated with delayed parasite clearance in genome-wide association studies (GWAS) in South-East Asia.
  • The presence of K13 mutations may indicate the emergence of a clonal population, supporting the need for elimination rather than containment in areas of resistance.
  • More research is needed to validate the relationship between African K13 mutations and resistance phenotypes.
  • K13 mutations may be part of a multigenic resistance mechanism, with secondary loci also playing a role.

• Definition of Artemisinin Resistance:

  • Suspected resistance is defined by a prevalence of ≥5% of any one K13 propeller mutation or ≥10% of all K13 mutations.
  • Confirmed resistance requires both K13 mutation prevalence and clinical or in vitro evidence of resistance.
  • Validation of K13 mutations requires in vitro assays such as the ring-stage assay (RSA) or transfection studies.

• Phenotypic Indicators:

  • Parasite clearance half-life is the most accurate in vivo indicator of artemisinin resistance.
  • Day 3 parasitemia is a useful surveillance tool, while RSA is the gold standard for in vitro validation.
  • The 5-hour clearance half-life cut-off is not absolute and depends on the proportion of resistant and sensitive strains and the estimator used.

• KARMA Project:

  • The KARMA study is a global effort to map the distribution of K13 alleles in blood samples collected after 2012.
  • Preliminary data from 42 institutions show that most countries (especially in South America) have no K13 mutants, except for one in Brazil.
  • 83 different K13 mutant alleles were identified, with 55% being novel and 80% of new alleles being private SNPs found in Africa, Asia, and Oceania.
  • The 446I allele is prevalent in China, and mutations in African parasites are distributed more evenly across the propeller domain compared to Asian ones.

• Genetic Architecture:

  • Artemisinin resistance is likely multigenic, with K13 as a central but not sole factor.
  • Background loci may serve as secondary markers, and gene flow studies can help understand the spread of resistance.
  • The role of immunity and partner drugs in the measurement of the in vivo phenotype must be considered.

• Transfection and In Vitro Studies:

  • Transfection studies show that K13 mutations are sufficient to cause resistance in vitro.
  • The RSA is the primary method for in vitro validation of K13 mutations.
  • The criteria for a "candidate" or "validated" K13 mutation include statistical significance and survival rates in in vitro assays.

• Partner Drug Resistance Markers:

  • Molecular markers for partner drugs (e.g., amodiaquine, mefloquine, lumefantrine, piperacine) are being explored.
  • Rotating ACTs with opposing or independent resistance mechanisms may help mitigate resistance.
  • Surveillance for partner drug resistance is recommended to support ACT efficacy.

• Public Health Recommendations:

  • A reference center for K13 genotyping is needed to standardize methods and provide guidance.
  • Molecular surveillance data should be shared publicly to support policy decisions.
  • Collaboration with local malaria control programs is essential to ensure effective use of molecular data.

Key Information

• K13 Mutations:

  • Linked to delayed parasite clearance in South-East Asia.
  • May be associated with resistance in Africa, though this requires further validation.
  • Include both spread and independent emergence, suggesting a need for elimination strategies.

• Phenotypic Surveillance:

  • Day 3 parasitemia is useful for monitoring.
  • Clearance half-life and RSA are more accurate but harder to implement in routine surveillance.

• Genetic Diversity:

  • African K13 mutations are more diverse and less concentrated than those in Asia.
  • Most African mutations are silent or low prevalence, indicating the need for more comprehensive studies.

• Data Sharing and Capacity Building:

  • Molecular data should be shared in the public domain to inform global malaria strategies.
  • Capacity building is crucial for countries to perform local sequencing and analysis.

• Future Research Needs:

  • Validation of African K13 mutations and their impact on resistance.
  • Understanding the role of secondary loci in resistance.
  • Conducting fitness studies on K13 mutations.
  • Investigating the relationship between artemisinin resistance and partner drug resistance.

Recommendations

• Engage Local Program Managers: To ensure that molecular surveillance data are used effectively in policy-making.
• Standardize Methods: Through a WHO reference center for K13 genotyping.
• Validate K13 Mutations: Using in vitro assays such as RSA or transfection studies.
• Promote Data Sharing: To support global malaria control efforts.
• Investigate African Mutations: To determine their relevance in resistance and inform strategies.
• Enhance Surveillance Frameworks: Incorporating gene flow and population structure data to guide elimination efforts.

Table of K13 Resistance Mutations