bird flu / H5N1 / HPAI

see also:

• influenza
• pandemics - influenza, coronavirus, Ebola

• of the influenza viruses, only type A influenza viruses infect birds, and all known subtypes can do so.
  • 15 subtypes of influenza virus are known to infect birds, thus providing an extensive reservoir of influenza viruses potentially circulating in bird populations. Migratory waterfowl, esp. wild ducks, are the natural reservoir of avian influenza viruses, and these birds are the most resistant to infection. Domestic poultry are particularly susceptible.
• if it causes high rates of severe infections with high mortality rates it is also known as highly pathogenic avian influenza (HPAI)
• Bird flu viruses do not usually infect humans, however, in 1997 in Hong Kong, an outbreak of H5N1 avian influenza marked the 1st known direct transmission of avian influenza virus from birds to humans. Since then H5, H7 and H9 avian influenza subtypes have been shown to infect humans.
  • the H5N1 virus has become the most concerning with its Z genotype and two distinct clades, the virus has become highly pathogenic (HPAI) - increasingly adapted to the environment, pathogenic in poultry and expansive in its mammalian host range. It has become endemic in many bird species in south-east Asia with a continuing international rate of spread. It has caused human disease outbreaks in 3 successive waves beginning in 2003
  • Australia has many wildlife species that could be devastated by an H5N1 outbreak.
    • many lack some of the genes that help fight viruses
    • animals which each birds are at high risk, including fur seals, Tasmanian tigers
      • by Mar 2025, 30,000 South American sea lions have died equal to around 10 per cent of the population, and 18,000 southern elephant seals have died
    • native birds are obviously at high risk including kookaburras and sulphur-crested cockatoos
    • kangaroos and koalas may be at high risk

• H5N1 uses haemagglutinin (HA) proteins to enter host cells¹⁾
• late 2021: after being quiet since 2015, avian influenza A (H5N1) clade 2.3.4.4b again re-emerges but with changed ecology and showed rapid global expansion in wild birds and farmed poultry and reached the USA
• Dec 2022, domestic cat dies from highly pathogenic avian influenza A (H5N1) clade 2.3.4.4b viral infection presumably acquired from nearby duck infections in France but had the E627K mutation in polymerase basic protein two which confers mammalian susceptibility
• in 2023, WHO reported low risk concerns of a potential human H5N1 pandemic as the global bird flu outbreaks have spread to mammals with evidence of it appearing to spread amongst minks from weasel to weasel. In the past year, there have been 10 human cases but no human-to-human spread as yet.
• in April 2023, a woman in China is the 3rd person infected with H3N8 and the 1st to die from it
• 2022 USA study announced Nov 2023, reports on HPAI H5N1 infections in non-avian mammals in US ²⁾
• mid-late 2023: an undetected single bird-to-cow transmission event in Texas leads to cow-to-cow spread of the virus from Texas to several other states, including North Carolina, Idaho, Michigan, Ohio, Kansas, and South Dakota ³⁾
• late 2023: H5N1 was found on the subantarctic islands of South Georgia, South Sandwich and also the Falklands after jumping from South America where more than 100,000 wild birds were reported dead in Peru alone
• human case of H5N1 brought to Victoria from India in Mar 2024
• global H7 bird flu outbreak arrived in Vic and WA in May 2024 and has spread to 67 dairy herds in nine US states and a 3rd dairy worker but currently has low transmissibility combined with mild symptoms although the 3rd case did have a more flu-like respiratory illness
• Apr 2024:. 1st lab confirmed human death from H5N2 bird flu - a 59yr old man in Mexico
• Dec 2024: Melbourne researchers suggest a 90% mortality rate in pregnant women who contract highly pathogenic avian influenza (HPAI) strains of H5N1 and H5N2
• Jan 2025: one of the earliest strains of bird flu isolated from a human in Texas shows a unique constellation of mutations that enable it to more easily replicate in human cells and cause more severe disease in mice compared to a strain found in dairy cattle. So far, most people infected experience mild illness and eye inflammation and the virus is not spreading between people.
• Mar 2025: avian influenza H5N1 2.3.4.4b continues to cause issues globally as it is highly pathogenic, and is evolving to infect mammals, in particular, seals, sea lions, cats and cattle (via avian receptors, an ancient biological hangover that remains with some modern mammals such as cattle), but now including sheep and sheep milk, and has become panzootic sparking concerns we may be on the brink of a human pandemic worse than Covid-19. It is now rampant in Europe, Asia, South America and the US, where it’s running wild in the poultry and dairy industries — not helped by Donald Trump’s new secretary of health and human services, Robert F Kennedy Jr, who advocates letting the virus rip. Fortunately, H5N1 is not yet airborne and does not spread easily to or between humans. Unlike COVID-19 that spreads through the air, H5N1 2.3.4.4b spreads most effectively by direct contact with secretions like saliva, mucus or faeces as well as ingesting dead animals or unpasteurised milk, itself a form of secretion. ⁴⁾
• May 2025: virus now infecting Antarctic seals with fur seals and elephant seals heavily impacted, while crabeater seals and Weddell seals have also died from the virus. Surprisingly, many penguins appear to be asymptomatic carriers. It has also reached the Kerguelen Islands with concerns it will jump to the Heard and McDonald islands and then to Macquarie Island and then to mainland Australia.⁵⁾