Universal primer set for amplification and sequencing of HA0 cleavage sites of all influenza A viruses

Sequence analysis of the endoproteolytic cleavage site within the hemagglutinin (HA) precursor protein HA(0) is fundamental for studies of the molecular biology of influenza A viruses, in particular, for molecular pathotyping of subtype H5 and H7 isolates. A current problem for routine diagnostics is the emergence of new strains of the H5 or H7 subtype or even other subtypes which escape detection by commonly used reverse transcription-PCR (RT-PCR) protocols. Here, the first pan-HA (PanHA) RT-PCR assay targeting the HA0 cleavage site of influenza A viruses of all 16 HA subtypes is reported. The assay was assessed in comparison to H5 and H7 subtype-specific RT-PCRs for the HA0 cleavage site and a real-time RT-PCR detecting the M gene. A panel of 92 influenza A viruses was used for validation. Sequence data for influenza A viruses from 32 allantoic fluid samples and 11 diagnostic swab samples of all 16 HA subtypes were generated by direct sequencing of the PanHA RT-PCR products. The results demonstrate that the new PanHA RT-PCR assay - followed by cycle sequencing - can complement existing methods and strengthen the reliability of influenza A virus diagnostics, allowing both molecular pathotyping (H5 and H7) and subtyping (non-H5 or -H7) within a single approach.