Outbreaks of H5N1 High Pathogenicity Avian Influenza in South Africa in 2023 Were Caused by Two Distinct Sub-Genotypes of Clade 2.3.4.4b Viruses

Abolnik, Celia; Roberts, Laura Christl; Strydom, Christine; Snyman, Albert; Roberts, David Gordon

doi:10.3390/v16060896

Cited by 2 publications

References 30 publications

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A 2022 avian H5N1 influenza A virus from clade 2.3.4.4b attaches to and replicates better in human respiratory epithelium than a 2005 H5N1 virus from clade 2.3.2.1

Bauer,

Leijten,

Iervolino

et al. 2024

Preprint

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Background: Highly pathogenic avian influenza (HPAI) H5 viruses of the A/Goose/Guangdong/1/1996 (GsGd) lineage pose significant global risks to wildlife, domestic animals, and humans. Recent cross-species transmission events to mammals, including humans, highlight this risk. Critical determinants for cross-species and intra-species transmission include the ability to attach to and replicate in respiratory epithelial cells. Although these factors have been studied for HPAI H5N1 viruses in the past, limited studies are available for currently circulating strains. Methods: We compared level of adaptation to human respiratory tract of a HPAI H5N1 clade 2.3.4.4b (H5N1.2022) virus with those of well characterized HPAI H5N1 clade 2.1.3.2 (H5N1.2005) and seasonal H3N2.2003 viruses by three methods. First, we compared pattern of virus attachment by virus histochemistry. Second, we compared efficiency of infection and replication, as well as innate immune responses in human respiratory epithelium in vitro. Lastly, we compared polymerase complex activity in a minigenome assay. Findings: The H5N1.2022 virus attached more abundantly to and replicated more efficiently in cells of the human respiratory tract compared to H5N1.2005 and H3N2.2003 viruses. This increased replication was not associated with an increased polymerase activity of H5N1.2022 virus compared to H3N2.2003 virus. The efficient replication of H5N1.2022 virus infection induced a robust innate immune response almost comparable to H3N2.2003. Interpretation: The pattern of virus attachment and replication efficiency of a HPAI H5N1.2022 virus resembled that of H3N2.2003 virus more closely than a HPAI H5N12005. This could contribute to an increased risk for both human infection and virus adaptations to humans.

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A 2022 avian H5N1 influenza A virus from clade 2.3.4.4b attaches to and replicates better in human respiratory epithelium than a 2005 H5N1 virus from clade 2.3.2.1

Bauer,

Leijten,

Iervolino

et al. 2024

Preprint

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Molecular and In Vivo Characterization of the High Pathogenicity H7N6 Avian Influenza Virus That Emerged in South African Poultry in 2023

Abolnik,

Phiri,

Strydom

et al. 2024

Transboundary and Emerging Diseases

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A high pathogenicity avian influenza (HPAI) subtype H7N6 virus emerged in South African poultry in 2023 and later spread to Mozambique, the first documented emergence of H7 HPAI in the African continent. A total of 6.82 million birds succumbed to the disease or were culled, representing about 20% of the South African egg‐laying flock and almost 30% of the broiler breeder flock. The complete genomes of 68 outbreak viruses were sequenced and analyzed, tracing the phylogenetic origins of the ancestral H7N6 virus to a reassortment of various subtypes that circulated in southern African wild birds. Molecular clock analysis determined that the virus emerged in the first week of May 2023, probably in a smallholder chicken flock, before spreading to commercial farms, where the disease was first reported in early June. The multibasic hemagglutinin protein cleavage site (HA0) was derived from a nonhomologous recombination event with chicken 28S ribosomal ribonucleic acid (RNA). Few genetic markers associated with an increased risk to humans were present in the translated viral proteins. The intravenous pathogenicity index (IVPI) value of the index case isolate was 1.67, reflecting that 50% of the specific pathogen‐free chickens died within 4 days of infection. Surviving birds showing mostly mild clinical signs and recovered by day 10 postinfection. Prior to death, chickens shed the virus primarily through the respiratory route, with lower amounts shed from the cloaca, but in the survivors, the virus was still being shed from the cloaca on day 10. Fomites were the likely source of disease spread between farms, and the amount of H7N6 HPAI virus per gram of feces was calculated at ~383,193 (5.58 log10) egg infectious dose 50 (EID50) equivalents, chicken feather follicles contained on average 739,712.43 (5.87 log10) EID50 equivalents, and 20 µg of feather dust contained 14,976.96 (4.175 log10) EID50 equivalents.

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Outbreaks of H5N1 High Pathogenicity Avian Influenza in South Africa in 2023 Were Caused by Two Distinct Sub-Genotypes of Clade 2.3.4.4b Viruses

Cited by 2 publications

References 30 publications

A 2022 avian H5N1 influenza A virus from clade 2.3.4.4b attaches to and replicates better in human respiratory epithelium than a 2005 H5N1 virus from clade 2.3.2.1

A 2022 avian H5N1 influenza A virus from clade 2.3.4.4b attaches to and replicates better in human respiratory epithelium than a 2005 H5N1 virus from clade 2.3.2.1

Molecular and In Vivo Characterization of the High Pathogenicity H7N6 Avian Influenza Virus That Emerged in South African Poultry in 2023

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