Bird Flu - An Animal Pandemic

06/04/2025

The Avian Influenza Panzootic- A(n) (non-human) animal pandemic.

“The loss of wildlife at the current scale presents an unprecedented risk of wildlife population collapse, creating an ecological crisis.”[1]‍

World Organisation for Animal Health, 13/03/24 “Wildlife under threat as avian influenza reaches Antarctica”

Since the autumn of 2021, one disease has caused the ‘biggest sudden drop of the world’s wild bird population in decades’, with at least 280 million birds having died[2]. The impact has been global, affecting nearly 500 bird species[3]. Victims include over 5000 common cranes in Israel (2021), over 20,000 Endangered Cape cormorants in South Africa (2021-2022)[4], 11,000 Scottish gannets (2022)[5], and 40% of all Peruvian pelicans, whose carcasses could be found littering the country’s beaches in early 2023[6]. More recently, 10,000 black-browed albatross have died in the Falkland Islands[7]. The disease behind these and the millions of other deaths in wild bird populations is a new variant of the bird flu virus H5N1, which was first detected in Europe in 2021. This strain of Highly Pathogenic Avian Influenza (HPAI) is especially well adapted to infect wild birds, and has a high mortality rate of up to 100%[8]. The current outbreak of avian influenza represents ‘the longest and largest in history’[9].

Avian Flu Spread to Other Animals

While the original H5N1 strain of HPAI, which initially evolved in intensive poultry farms, has been around since 1996[10], this very infectious and highly transmissible novel variant we are now facing marks a significant change. Not only has it proved particularly effective at circulating in wild bird populations, but it has also spread to a wide range of other wild animals, and is now found on every continent except Australia/Oceania. Since 2021, HPAI has infected at least 48 new mammal species[11]. In 2023, it killed a staggering 24,000 sea lions in South America[12]. In Argentina alone, 17,000 elephant seal pups died – equating to 96% of the pups born there in 2023, and representing almost a generation of seals[13]. Elsewhere, it has killed sea otters, foxes, cougars, coyotes, badgers, martens, dolphins and a polar bear[14], among other species.

Meanwhile, zoo animals – including species of significant concern to conservation – have also succumbed to the virus[15]. Most notably, according to state media, 47 captive tigers died from HPAI in Vietnam in 2024, along with three lions and a panther (likely as a result of feeding with infected poultry)[16].

‍Continued Transmission in Domestic Animals

HPAI continues to spread in domestic animals too, causing significant global economic concern and a currently low but undoubtedly increasing risk to human health. Following a record number of outbreaks in domestic birds in Europe in 2021-2022[17], it’s now also circulating widely in dairy cattle in the US, most likely having been spread by non-biosecure milking practices. By March this year, it had been found in 957 herds across 16 states[18], and resulted in 67 cases in humans who had close contact with cows[19]. Nearly half of California’s 1,300 farms have been affected[20].

These dairy cattle outbreaks represent ‘one of the first times that we are seeing evidence of efficient and sustained mammalian-to-mammalian transmission’[21] (between cows and from cows to cats and a raccoon). The disease is, arguably, only ‘one mutation away from being able to spread between humans’[22]. While the strain circulating in cattle is currently mild, ‘the number of people infected and rapidness with which it is mutating are concerning to virologists and public health officials’[23]. In February 2025, the European Centre for Disease Prevention and Control acknowledged that avian influenza viruses are posing ‘an increasing threat, with the potential to adapt to humans and trigger future pandemics’[24]. Meanwhile, the first case in a sheep has just been recorded in England[25].

‍Vets Have a Vital Role To Play

While the economic and zoonotic risks of avian influenza certainly shouldn’t be underestimated, it’s vital that we take the risk to wildlife – and especially species already threatened with extinction – very seriously indeed. Although there is no silver bullet or quick solution, it’s essential that we continue to develop coordinated, multidisciplinary responses to tackle this animal pandemic. All those involved in species conservation have a key role to play in protecting wildlife by helping predict and prevent future spillover events where possible.

Vets, biologists and zoologists need to be actively involved in developing improved surveillance strategies in order to better understand the spread and evolution of avian influenza.

A key part of that process is knowing how to sample correctly and accurately test for the virus regularly and extensively, and what preventative measures to put in place where possible and appropriate. These can include limiting supplementary feeding of wild bird populations, minimising disruption of breeding colonies by human traffic and the removal of dead birds where feasible. In some limited circumstances, it may also involve vaccination[26].

‍Avian Flu is a Threat We Cannot Afford to Ignore

Highly Pathogenic Avian Influenza is just one example of a serious disease threat facing wildlife today, but it’s the speed and nature of its spread, combined with its high mortality rate in birds and other animals that makes it of particular concern right now. In the words of Dr. Christian Walzer, Executive Director of Health at the Wildlife Conservation Society, ‘H5N1 now presents an existential threat to the world’s biodiversity’[27].

‍WVI exists to help train local vets, biologists and zoologists to become the most effective disease detectives they can be, in order to contribute to the fight against this and many other pathogens which threaten the health of all species that share the planet.

[1] https://www.woah.org/en/wildlife-under-threat-as-avian-influenza-reaches-antarctica/

[2] https://www.theguardian.com/environment/article/2024/sep/04/forgotten-epidemic-with-over-280-million-birds-dead-how-is-the-avian-flu-outbreak-evolving

[3] https://www.wildanimalinitiative.org/blog/how-avian-flu-affects-wild-birds#:~:text=At%20least%20485%20bird%20species,on%20every%20continent%20except%20Australia.

[4] https://datazone.birdlife.org/articles/an-unprecedented-global-epizootic-of-avian-influenza-is-causing-mass-mortality-of-wild-birds

[5] https://www.rspb.org.uk/birds-and-wildlife/seabird-surveys-project-report

[6]https://communities.springernature.com/posts/mass-die-offs-of-marine-birds-and-mammals-in-peru-sound-the-alarm-on-the-spread-of-highly-pathogenic-avian-influenza-h5n1-viruses-throughout-south-america#:%7E:text=Early%20in%202023%20Peru's%20pristine,quickly%20moving%20down%20the%20coast.

[7] https://www.gavi.org/vaccineswork/how-bird-flu-affecting-animal-populations#:~:text=H5N1%20has%20already%20impacted%20at,this%20virus%20has%20spread%20globally

[8] https://datazone.birdlife.org/articles/an-unprecedented-global-epizootic-of-avian-influenza-is-causing-mass-mortality-of-wild-birds

[9] https://www.vet.cornell.edu/highly-pathogenic-avian-influenza-bird-flu-resource-center/wildlife#:~:text=Which%20wildlife%20species%20have%20been,of%20virus%20shed%20in%20water.

[10] https://datazone.birdlife.org/articles/an-unprecedented-global-epizootic-of-avian-influenza-is-causing-mass-mortality-of-wild-birds

[11] https://wwwnc.cdc.gov/eid/article/30/3/23-1098_article

[12] https://www.sciencedirect.com/science/article/pii/S1477893924000267