Avian influenza, new aspects of an old threat

Zoonotic infections by avian influenza virus: changing global epidemiology, investigation, and control

Avian influenza virus continues to pose zoonotic, epizootic, and pandemic threats worldwide, as exemplified by the 2020-23 epizootics of re-emerging H5 genotype avian influenza viruses among birds and mammals and the fatal jump to humans of emerging A(H3N8) in early 2023. Future influenza pandemic threats are driven by extensive mutations and reassortments of avian influenza viruses rooted in frequent interspecies transmission and genetic mixing and underscore the urgent need for more effective actions. We examine the changing global epidemiology of human infections caused by avian influenza viruses over the past decade, including dramatic increases in both the number of reported infections in humans and the spectrum of avian influenza virus subtypes that have jumped to humans. We also discuss the use of advanced surveillance, diagnostic technologies, and state-of-the-art analysis methods for tracking emerging avian influenza viruses. We outline an avian influenza virus-specific application of the One Health approach, integrating enhanced surveillance, tightened biosecurity, targeted vaccination, timely precautions, and timely clinical management, and fostering global collaboration to control the threats of avian influenza viruses.

H5N1 high pathogenicity avian influenza virus in migratory birds exhibiting low pathogenicity in mallards increases its risk of transmission and spread in poultry

In 2020, an H5N1 avian influenza virus of clade 2.3.4.4b was detected in Europe for the first time and was spread throughout the world by wild migratory birds, resulting in the culling of an unprecedented number of wild birds and poultry due to the epidemic. In February 2023, we isolated and identified a strain of H5N1 high pathogenicity avian influenza virus from a swab sample from a grey crane in Ningxia, China. Phylogenetic analysis of the Hemagglutinin (HA) gene showed that the virus belonged to clade 2.3.4.4b, and several gene segments were closely related to H5N1 viruses infecting humans in China. Analysis of key amino acid sites revealed that the virus contained multiple amino acid substitutions that facilitate enhanced viral replication and mammalian pathogenicity. The results of animal challenge experiments showed that the virus is highly pathogenic to chickens, moderately pathogenic to BALB/c mice, and highly infectious but not lethal to mallards. Moreover, the virus exhibited minor antigenic drift compared with the H5-Re14 vaccine strain. To this end, we need to pay more attention to the monitoring of wild birds to prevent further spread of viruses to poultry and mammals, including humans.

Baloxavir marboxil use for critical human infection of avian influenza A H5N6 virus

BACKGROUND

Recent outbreaks of avian influenza and ongoing virus reassortment have drawn focus on spill-over infections. The increase in human infections with highly pathogenic avian influenza H5N6 virus and its high fatality rate posed a potential threat, necessitating the search for a more effective treatment.

METHODS

Longitudinal clinical data and specimens were collected from five H5N6 patients after admission. All patients received antiviral treatment of either sequential monotherapy of oseltamivir and baloxavir or the two drugs in combination. Severity of illness; viral load in sputum, urine, and blood; and cytokine levels in serum and sputum were serially analyzed.

FINDINGS

All patients developed acute respiratory distress syndrome (ARDS) and viral sepsis within 1 week after disease onset. When delayed oseltamivir showed poor effects, baloxavir was administered and rapidly decreased viral load. In addition, levels of IL-18, M-CSF, IL-6, and HGF in sputum and Mig and IL-18 in serum that reflected ARDS and sepsis deterioration, respectively, were also reduced with baloxavir usage. However, three patients eventually died from exacerbation of underlying disease and secondary bacterial infection. Nonsurvivors had more severe extrapulmonary organ dysfunction and insufficient H5N6 virus-specific antibody response.

CONCLUSIONS

For critical human cases of H5N6 infection, baloxavir demonstrated effects on viral load and pulmonary/extrapulmonary cytokines, even though treatment was delayed. Baloxavir could be regarded as a first-line treatment to limit continued viral propagation, with potential future application in avian influenza human infections and poultry workers exhibiting influenza-like illness.

FUNDING

This work was funded by the National Natural Science Foundation of China (81761128014).