Abstract
Objectives: In order to develop a multiplex RT-PCR assay using the GeXP analyser for the simultaneous detection of four different NA serotypes of H5-subtype AIVs, effective to control and reduce H5 subtype of avian influenza outbreak. Design: Six pairs of primers were designed using conserved and specific sequences of the AIV subtypes H5, N1, N2, N6 and N8 in GenBank. Each gene-specific primer was fused at the 5' end to a universal sequence to generate six pairs of chimeric primers, and one pair of universal primers was used for RT-PCR, and PCR product separation and detection were performed by capillary electrophoresis using the GenomeLab GeXP genetic analysis system. Setting: Single and mixed avian pathogen cDNA/DNA templates were employed to evaluate the specificity of a multiplex assay with a GeXP analyser. Corresponding specific DNA products were amplified for each gene, revealing amplification peaks for M, H5, N1, N2, N6 and N8 genes from four different NA subtypes of influenza A H5 virus. Sample: A total of 180 cloacal swabs were collected from poultry at live bird markets. Main outcome measures: The multiplex PCR assay demonstrated excellent specificity, with each pair of specific primers generating only products corresponding to the target genes and without cross-amplification with other NA-subtype influenza viruses or other avian pathogens. Using various premixed ssRNAs containing known AIV target genes, the detection limit for the multiplex assay was determined to be 10(2) copies/μl. The GeXP assay was further evaluated using 180 clinical specimens and compared with RRT-PCR (real-time reverse transcriptase PCR) and virus isolation. Conclusions: This GeXP analyser-based multiplex assay for four different NA subtypes of H5 HPAI viruses is both highly specific and sensitive and can be used as a rapid and direct diagnostic assay for testing clinical samples.