Antibodies to Highly Pathogenic A/H5Nx (Clade 2.3.4.4) Influenza Viruses in the Sera of Vietnamese Residents

Assessing potential pathogenicity of novel highly pathogenic avian influenza (H5N6) viruses isolated from Mongolian wild duck feces using a mouse model

Several novel highly pathogenic avian influenza (HPAIVs) A(H5N6) viruses were reported in Mongolia in 2020, some of which included host-specific markers associated with mammalian infection. However, their pathogenicity has not yet been investigated. Here, we isolated and evaluate two novel genotypes of A(H5N6) subtype in Mongolia during 2018–2019 (A/wildDuck/MN/H5N6/2018-19). Their evolution pattern and molecular characteristics were evaluated using gene sequencing and their pathogenicity was determined using a mouse model. We also compared their antigenicity with previous H5 Clade 2.3.4.4 human isolates by cross-hemagglutination inhibition (HI). Our data suggests that A/wildDuck/MN/H5N6/2018-19 belongs to clade 2.3.4.4h, and maintains several residues associated with mammal adaptation. In addition, our evaluations revealed that their isolates are less virulent in mice than the previously identified H5 human isolates. However, their antigenicity is distinct from other HPAIVs H5 clade 2.3.4.4, thus supporting their continued evaluation as potential infection risks and the preparation of novel candidate vaccines for their neutralization.

Development of a Rapid Fluorescent Diagnostic System for Early Detection of the Highly Pathogenic Avian Influenza H5 Clade 2.3.4.4 Viruses in Chicken Stool

Rapid diagnosis is essential for the control and prevention of H5 highly pathogenic avian influenza viruses (HPAIVs). However, highly sensitive and rapid diagnostic systems have shown limited performance due to specific antibody scarcity. In this study, two novel specific monoclonal antibodies (mAbs) for clade 2.3.4.4 H5Nx viruses were developed by using an immunogen from a reversed genetic influenza virus (RGV). These mAbs were combined with fluorescence europium nanoparticles and an optimized lysis buffer, which were further used for developing a fluorescent immunochromatographic rapid strip test (FICT) for early detection of H5Nx influenza viruses on chicken stool samples. The result indicates that the limit of detection (LoD) of the developed FICT was 40 HAU/mL for detection of HPAIV H5 clade 2.3.4.4b in spiked chicken stool samples, which corresponded to 4.78 × 10⁴ RNA copies as obtained from real-time polymerase chain reaction (RT-PCR). An experimental challenge of chicken with H5N6 HPAIV is lethal for chicken three days post-infection (DPI). Interestingly, our FICT could detect H5N6 in stool samples at 2 DPI earlier, with 100% relative sensitivity in comparison with RT-PCR, and it showed 50% higher sensitivity than the traditional colloidal gold-based rapid diagnostic test using the same mAbs pair. In conclusion, our rapid diagnostic method can be utilized for the early detection of H5Nx 2.3.4.4 HPAIVs in avian fecal samples from poultry farms or for influenza surveillance in wild migratory birds.