A(H5N1) Flu Arrives in North America, Raising Fears of Potential Pandemic

A recent study published in the journal Nature CommunicationsResearchers examined the phenotypic and genetic evolution of highly pathogenic avian influenza A(H5N1) viruses of clade 2.3.4.4b after their spread in North America (NAm).

Clade 2.3.4.4b A(H5N1) viruses rapidly spread across Africa, Europe and Asia in 2021, infecting livestock and wild birds. Viruses of the same clade were discovered in the North American region towards the end of 2021, indicating continued transcontinental spread. There are concerns about potential zoonotic transmission, reassortment, and increased virulence of viruses and human infections.

study: Rapid evolution of A(H5N1) influenza virus after intercontinental spread to North America. Image credits: CDC and NIAID

About research

In this study, researchers reported the rapid evolution of the A(H5N1) influenza virus after its intercontinental spread to North America.

Transmission dynamics of two A(H5N1) wild bird viruses, A/American Wigeon/South Carolina/22-000345-001/2021 (Wigeon/SC/21) and A/Bald Eagle/Florida/ collected in December 2021 and Pathogenesis W22-134-OP/2022 obtained in February 2022 was determined. Ferrets and White Leghorn chickens were used to assess A(H5N1) virus infection. Genotypic and antigenic analyzes of clade 2.3.4.4b viruses were performed to identify other virus types of the same clade among ferrets.

To assess toxicity, nasal wash titers were determined and expressed as: Median tissue culture infectious dose (TCID₅₀/ml), followed by histopathological examination of ferret upper, lower, and extrapulmonary tissues. In addition, BALB/c mice were inoculated with virus to determine whether virulence and virulence among ferrets could be mirrored in other mammalian models of influenza. median lethality (LD₅₀) dose was determined to assess the lethality of the virus. A syncytium assay was performed to detect pH of hemagglutinin (HA) activation and a reporter gene assay was performed to assess viral polymerase gene activity.

Undifferentiated human airway epithelial cells (Calu-3) and primary differentiated human airway cultures were used to assess replication kinetics. Sera were collected from 48 of her individuals aged 18.0–46.0 years to measure cross-protective antibodies targeting the influenza virus neuraminidase (NA) protein using an enzyme-linked lectin assay (ELLA). Antiviral susceptibility of clade 2.3.4.4b viruses was measured using the NA inhibitors (NAI), zanamivir and oseltamivir, and the active metabolite of the endonuclease inhibitor baloxavir marboxil, baloxaviric acid (BXA).

result

Viral transmission between birds and mammals was minimal. In ferrets, inoculation with wigeon/SC/21 and eagle/FL/22 caused mild and severe infections, respectively. This is evidenced by the more significant mean titers of Eagle/FL/22 nasal wash after 1, 3, and 5 days. – infection (dpi). 2.3.4.4b Following the western migration of the clade, the introduction of A(H5N1) viruses into North America was quickly followed by reassortment events of NAm wild avian influenza virus and H5 2.3.4.4b viral organisms, As a result, different ribonucleoprotein gene combinations were obtained. .

For example, Eagle/FL/22 developed the North American wild bird nucleoprotein (NP), and polymerase basic (PB)-1 and 2 genes after reassortment. Among the sequenced 58.0 A(H5N1) influenza viruses, he detected four viral genotypes. All viruses contained NA, HA, nonstructural (NS), and matrix (M) gene segments of Eurasian (EA) origin, but had different Nam- or EA-origin NP and polymerase gene combinations. rice field. In most cases, monophyletic NAm segments were observed, indicating minimal reassortment due to the resulting geographic spread of the virus.

NAm strain A(H5N1) viral proteins showed no markers associated with mammalian virulence and were all antigenically uniform. An additional typed virus was A/Red Shoulder Hawk/North Carolina/W22-121/2022 (Hawk/NC/22). A/Fancy Chicken/Newfoundland/FAV-0033/2021 (Ck/NL/21); A/Bald Eagle/North Carolina/W22-140/2022 (Eagle/North Carolina/22); A/Helmet Wasp/Georgia/W22- 145E/2022 (Wasp/GA/22). Acquisition of NAm segments is strongly correlated with disease severity in ferrets, with Ck/NL/21, which lacks the NAm gene, being the least infected and Scaup/GA/22, which has four NAm genes, being the most severe. Met.

This trend extended to viral replication in tissues and histopathological findings. Her LD was lowest for viruses that gave her 100% lethality in ferrets and viruses that acquired her NAm segment such as Scaup/GA/22, Hawk/NC/22 and Eagle/FL/22.₅₀ Values ​​among mice. Eagle/FL/22 and Wigeon/SC/21 showed polymerase activity similar to avian receptor specificity, although there were some differences in replication rates between Calu-3 cells and human airway cultures. bottom.

Antibody titers targeting Eagle/FL/22 and Wigeon/SC/21 N1 were comparable to those against seasonal CA/04 (H1N1)pdm09 NA, and the NA protein of H5N1 virus was isolated from A(H1N1)pdm09 virus. showed 90% similarity with . Median effective concentration (EC₅₀) and half the maximum inhibitory concentration (IC₅₀) values ​​for the native and reassortant viruses tested were similar to those for the drug-susceptible human A(H1N1)pdm09 influenza virus.

Overall, the study results emphasized that the current A(H5N1) 2.3.4.4b virus lineage is prone to reassortant and attack the brain and spinal cord. This finding calls for coordinated preparations to combat viral evolution and continent-wide spread and limit the impact of pandemics caused by similar A(H5N1) reassortant viruses.