Genetic properties and pathogenicity of a novel reassortant H10N5 influenza virus from wild birds

A Retrospective Investigation of a Case of Dual Infection by Avian-Origin Influenza A (H10N5) and Seasonal Influenza A (H3N2) Viruses - Anhui Province, China, December 2023-January 2024

What is known about this topic?

H10 avian influenza viruses circulate in wild birds and can reassort with other subtypes. H10N8 and H10N3 have previously caused sporadic human infections in China.

What is added by this report?

This report documents the first human case of co-infection with avian-origin H10N5 and seasonal H3N2 influenza viruses. Epidemiological investigations identified H10N5 in environmental samples linked to the patient, but no transmission to close contacts occurred.

What are the implications for public health practice?

Enhanced surveillance of avian influenza in live poultry markets and poultry populations is crucial for thoroughly characterizing the epidemiology, transmission, and pathogenesis of H10N5 viruses. Strengthening assessments of outbreak control measures is essential to guide effective management.

Pathogenesis and genetic characteristics of low pathogenic avian influenza H10 viruses isolated from migratory birds in South Korea during 2010-2019

Human infection by avian-origin subtype H10 influenza viruses has raised concerns about the pandemic potential of these microbes. H10 subtype low pathogenic avian influenza viruses (LPAIVs) have been isolated from wild birds and poultry worldwide. Here, we isolated 36 H10 LPAIVs from wild bird habitats (a mean annual rate of 3.8% of all avian influenza virus isolations) from January 2010 to April 2019 through a nationwide active surveillance program for avian influenza viruses (AIVs). Phylogenetic analysis revealed that the haemagglutinin (HA) gene of H10 isolates formed eight distinct genetic subgroups (HA-A-H). Unlike other Eurasian-origin subgroups, the HA-H subgroup belonged to the North American lineage. Gene-constellation analysis revealed that 24 H10 LPAIVs constituted ≥18 distinct genotypes, representing high levels of genetic diversity. An intravenous pathogenicity index (IVPI) experiment showed that the pathogenicity of representative strains of the HA-B, E and G subgroups possessing an IVPI score >1.2 was associated with replication capacity in the chicken kidney in the absence of trypsin. Intranasal inoculation experiments showed that a representative strain of the HA-D subgroup replicated and transmitted in chickens without clinical signs. Subclinical virus shedding in chickens may contribute to its silent spread among the poultry population. Moreover, six representative viruses replicated in the lungs of mice without prior adaptation and a representative strain of the HA-C subgroup caused 40% mortality, with severe body weight loss. These findings highlight the importance of intensive surveillance of wild bird habitats, poultry farms and the animal-human interface, along with appropriate risk assessment of isolated viruses.

Development of a TaqMan MGB RT-PCR assay for the detection of type A and subtype H10 avian influenza viruses

H10 subtype avian influenza viruses have caused several epidemics in poultry and mammals, and specific, rapid and sensitive methods for detection are urgently needed. Herein, TaqMan minor groove binder (MGB) probes and multiplex real-time RT-PCR primers were designed based on gene regions encoding conserved domains of the nucleoprotein and H10 hemagglutinin. The developed multiplex real-time RT-PCR assay displayed high specificity, repeatability, and a detection limit of 10 copies per reaction. This diagnostic method could prove valuable for the rapid detection of H10 subtype AIVs in China.

Multiple adaptive amino acid substitutions increase the virulence of a wild waterfowl-origin reassortant H5N8 avian influenza virus in mice

A novel H5N8 highly pathogenic avian influenza virus (HPAIV) caused poultry outbreaks in the Republic of Korea in 2014. The novel H5N8 HPAIV has spread to Asia, Europe, and North America and caused great public concern from then on. Here, we generated mouse-adapted variants of a wild waterfowl-origin H5N8 HPAIV to identify adaptive mutants that confer enhanced pathogenicity in mammals. The mouse lethal doses (MLD₅₀) of the mouse-adapted variants were reduced 31623-fold compared to the wild-type (WT) virus. Mouse-adapted variants displayed enhanced replication in vitro and in vivo, and expanded tissue tropism in mice. Sequence analysis revealed four amino acid substitutions in the PB2 (E627K), PA (F35S), HA (R227H), and NA (I462V) proteins. These data suggest that multiple amino acid substitutions collaboratively increase the virulence of a wild bird-origin reassortant H5N8 HPAIV and cause severe disease in mice.

Multiple amino acid substitutions involved in the virulence enhancement of an H3N2 avian influenza A virus isolated from wild waterfowl in mice

Frequent emergence of low pathogenic avian influenza H3N2 viruses in the wild birds has caused concern for human health. Here, we generated mouse-adapted strains of a wild waterfowl-origin low pathogenic avian influenza H3N2 virus to identify adaptive mutations that confer enhanced virulence in mammals. The mouse lethal doses (MLD₅₀) of the adapted strains were reduced >562-fold compared to the parental virus. Mouse-adapted strains displayed enhanced replication in vitro and in vivo, and acquired the ability to replicate in extrapulmonary tissues. These observations suggest that enhanced growth characteristics and modified cell tropism may increase the virulence of H3N2 AIVs in mice. Genomic analysis revealed mutations in the PB2 (E192K and D701N), PB1 (F269S, I475V, and L598P), HA (V242E), NA (G170R), and M1 (M192V) proteins. Our results suggest that these amino acid substitutions collaboratively enhance the ability of H3N2 avian influenza A virus to replicate and cause severe disease in mammals.