WHO/BS/2017.2330 Collaborative Study to Evaluate a Candidate WHO IS for Chikungunya Virus for Nucleic Acid Amplification Technique (NAT)-Based Assays
Overview
This report describes the World Health Organization (WHO) project to develop an international standard (IS) for Chikungunya virus (CHIKV) RNA for the use with nucleic acid amplification technique (NAT)-based assays. An international collaborative study was conducted to determine the potency of the candidate standard using a range of NAT-based assays for CHIKV, and to evaluate the suitability of the candidate for the calibration of secondary reference materials and the standardization of CHIKV viral load measurements.
The candidate standard consisted of an heat inactivated CHIKV strain of the East/South/Central African genotype (ESCA), isolated from a patient returning from India to the United States in 20061 , diluted in human negative plasma. The lyophilized candidate preparation (Sample 1), the corresponding liquid-frozen bulk material (Sample 2) and three different clinical samples (Sample 3, Sample 4 and Sample 5) were included in the collaborative study. Twenty-five laboratories representing 14 countries participated in the study to evaluate the material using their routine CHIKV NAT assays. Twenty-four laboratories returned 31 data sets from 17 commercial assays and 14 in-house methods. Of these 31 methods, 11 were quantitative and 20 were qualitative.
The results of the study indicate the suitability of the candidate material of the CHIKV strain of ESCA genotype (Sample 1) as the proposed 1st WHO IS for CHIKV. It is therefore proposed that the candidate material (PEI code 11785/16) is established as the 1st WHO IS for CHIKV RNA for NAT-based assays with an assigned potency of 2,500,000 International Units (IU)/mL when reconstituted in 0.5 mL of nuclease-free water.
On-going studies for real-time and accelerated stability of the proposed IS indicate that the preparation is stable and suitable for long-term use at the proposed storage conditions.