Clinical features of the first critical case of acute encephalitis caused by avian influenza A (H5N6) virus

Avian influenza virus cross-infections as test case for pandemic preparedness: From epidemiological hazard models to sequence-based early viral warning systems

Pandemic preparedness starts with an early warning system of viruses with a pandemic potential. Based on information collected in a multitude of surveys, hazard models were developed identifying influenza viruses presenting a pandemic threat. Scores are attributed for 10 viral traits by expert panels which identified avian influenza viruses (AIV) belonging to subtypes H7N9 and H5N1 as representing the greatest pandemic risk. In 2013, more than 100 human cases infected with AIV H7N9 were observed in China. Case fatality rate (CFR) was high (27%), but the human-to-human transmission rate was low and by serological evidence H7N9 did not spread widely. Nevertheless, until 2019 more than 1500 H7N9 patients were identified characterized by a high CFR of 39%. Serology demonstrated that mild infections with H7N9 were widespread. In 2003, more than 400 people experienced AIV H7N7 cross-infection causing mainly conjunctivitis during a large poultry epidemic in The Netherlands. Between 1996 and 2019, a total of 881 human infections with avian H5N1 viruses were documented showing a CFR of 52%. Outbreaks were centred on South East Asia and showed close associations with epizootics in poultry. Mutations predisposing to human cross-infections were identified in the haemagglutinin (HA) and the RNA polymerase subunit PB2 of human H7N9 isolates. Human H5N1 isolates showed mutations in the receptor binding domain of HA and transmission in mammals could be obtained by as few as four additional aa changes introduced experimentally. Researchers have defined viral point mutations in HA, PB2 and the nucleoprotein NP that allowed AIV to cross the species barrier to mammals with respect to receptor recognition, RNA replication and escape from innate immunity respectively. Based on this insight a sequence-based early warning system for AIV preadapted to human transmission could be envisioned. Mink farms and live poultry markets are prime targets for such sequencing efforts.

A murine monoclonal antibody against H5N1 avian influenza virus cross-reacts with human kidney cortex cells

To investigate the biological characteristics of monoclonal antibodies (mAbs) against avian influenza virus (AIV) and the possible mechanism of AIV-related kidney injury. BALB/c mice were immunized with inactivated H5N1 AIV to prepare monoclonal antibody H5-32, and its subtype, titer and cross-reactivity with other influenza viruses were identified. The reactivity of monoclonal antibody with normal human tissue was analyzed by immunohistochemistry. Immunofluorescence and confocal laser scanning technique were used to detect the binding sites between mAb and human renal cortical cells, and Western blotting was used to detect the size of binding fragments. Immunohistochemical analysis confirmed that monoclonal antibody H5-32 cross-reacted with normal human kidney tissue. In human kidney, mAb H5-32 was localized in the cytoplasm of human renal tubular epithelial cells, and its binding fragment size was about 43 kDa. H5N1 AIV appears to bind to human renal tubular epithelial cells, which may be one of the mechanisms of kidney injury caused by AIV infection.

The neuropathogenesis of highly pathogenic avian influenza H5Nx viruses in mammalian species including humans

Circulation of highly pathogenic avian influenza (HPAI) H5Nx viruses of the A/Goose/Guangdong/1/96 lineage in birds regularly causes infections of mammals, including humans. In many mammalian species, infections are associated with severe neurological disease, a unique feature of HPAI H5Nx viruses compared with other influenza A viruses. Here, we provide an overview of the neuropathogenesis of HPAI H5Nx virus infection in mammals, centered on three aspects: neuroinvasion, neurotropism, and neurovirulence. We focus on in vitro studies, as well as studies on naturally or experimentally infected mammals. Additionally, we discuss the contribution of viral factors to the neuropathogenesis of HPAI H5Nx virus infections and the efficacy of intervention strategies to prevent neuroinvasion or the development of neurological disease.

Exploring the Correlation Between Influenza A Virus (H3N2) Infections and Neurological Manifestations: A Scoping Review

Influenza A virus (IAV), particularly the H3N2 variant, is known to cause respiratory manifestations, but it can also lead to neurological complications ranging from mild symptoms like headache and dizziness to severe conditions such as encephalitis and acute necrotizing encephalopathy (ANE). In this article, the correlation between the H3N2 variant of the IAV and neurological manifestations is discussed. Additionally, prompt recognition and treatment of influenza-associated neurological manifestations are highlighted to prevent infection-related long-term complications. This review briefly discusses various neurological complications linked to IAV infections, such as encephalitis, febrile convulsions, and acute disseminated encephalomyelitis, and the potential mechanisms involved in the development of neurological complications.

Key amino acid position 272 in neuraminidase determines the replication and virulence of H5N6 avian influenza virus in mammals

Avian influenza H5N6 virus not only wreaks economic havoc in the poultry industry but also threatens human health. Strikingly, as of August 2022, 78 human beings were infected with H5N6, and the spike in the number of human infections with H5N6 occurred during 2021. In the life cycle of influenza virus, neuraminidase (NA) has numerous functions, especially viral budding and replication. Here, we found that NA-D272N mutation became predominant in H5N6 viruses since 2015 and significantly increased the viral replication and virulence in mice. D272N mutation in NA protein increased viral release from erythrocytes, thermostability, early transcription, and accumulation of NA protein. Particularly, the dominant 272 residue switch from N to S has occurred in wild bird-origin H5N6 viruses since late 2016 and N272S mutation induced significantly higher levels of inflammatory cytokines in infected human cells. Therefore, comprehensive surveillance of bird populations needs to be enhanced to monitor mammalian adaptive mutations of H5N6 viruses.

Updating the National Antigen Bank in Korea: Protective Efficacy of Synthetic Vaccine Candidates against H5Nx Highly Pathogenic Avian Influenza Viruses Belonging to Clades 2.3.2.1 and 2.3.4.4

Since 2018, Korea has been building an avian influenza (AI) national antigen bank for emergency preparedness; this antigen bank is updated every 2 years. To update the vaccine strains in the antigen bank, we used reverse genetics technology to develop two vaccine candidates against avian influenza strains belonging to clades 2.3.2.1d and 2.3.4.4h, and then evaluated their immunogenicity and protective efficacy in SPF chickens challenged with H5 viruses. The two vaccine candidates, named rgCA2/2.3.2.1d and rgES3/2.3.4.4h, were highly immunogenic, with hemagglutination inhibition (HI) titers of 8.2−9.3 log2 against the vaccine strain, and 7.1−7.3 log2 against the lethal challenge viruses (in which the HA genes shared 97% and 95.4% homology with that of rgCA2/2.3.2.1d and rgES3/2.3.4.4h, respectively). A full dose of each vaccine candidate provided 100% protection against the challenge viruses, with a reduction in clinical symptoms and virus shedding. A 1/10 dose provided similar levels of protection, whereas a 1/100 dose resulted in mortality and virus shedding by 7 dpi. Moreover, immunity induced by the two vaccines was long lasting, with HI titers of >7 log2 against the vaccine strain remaining after 6 months. Thus, the two vaccine candidates show protective efficacy and can be used to update the AI national antigen bank.