Comparison of nucleic acid extraction methods for next-generation sequencing of avian influenza A virus from ferret respiratory samples

Influenza A virus is a negative-sense RNA virus with a segmented genome consisting of eight RNA segments. Avian influenza A virus (AIV) primarily infects avian hosts and sporadically infects mammals, which can lead to adaptation to new species. Next-generation sequencing (NGS) of emerging AIV genomes extracted from respiratory samples collected on sequential days from animal models and clinical patients enables analysis of the emergence of evolutionary variants within the virus population over time. However, obtaining codon complete AIV genome at a sufficient coverage depth for nucleotide variant calling remains a challenge, especially from post-inoculation respiratory samples collected at late time points that have low viral titers. In this study, nasal wash samples from ferrets inoculated with different subtypes of AIV were collected on various days post-inoculation. Each nasal wash sample was aliquoted and extracted using five commercially available nucleic acid extraction methods. Extracted influenza virus RNA was amplified and NGS conducted using Illumina Mi-Seq. For each nasal wash sample, completeness of AIV genome segments and coverage depth were compared among five extraction methods. Nucleic acids extracted by MagNA pure compact RNA isolation consistently yielded codon complete sequences for all eight genome segments at the required coverage depth at each time point sampled. The study revealed that DNase treatment was critical to the amplification of influenza genome segments and the downstream success of codon complete NGS from nasal wash samples. The findings from this study can be applied to improve NGS of influenza and other RNA viruses that infect the respiratory tract and are collected from respiratory samples.