Largest global bird flu outbreak ‘in history’ shows no sign of slowing

A lethal bird flu outbreak that has been circling the globe since 2021 peaked in Japan this week, as an agriculture ministry official said on Tuesday the country plans to cull more than 10 million chickens at risk of exposure to the virus. 

Flu is a common annual illness among wild birds yet the H5N1 strain now sweeping Japan is uniquely contagious and deadly. It poses such high risk to farmed birds, such as chickens and turkeys, that a single infection on a farm condemns the entire flock to be killed. As outbreaks in Japan have reached a record high, the cull is the largest ever planned for the yearly flu season that runs from October to May.  

Around the globe, record-breaking death tolls due to the virus are becoming the norm. In the US, more states than ever before have reported instances of bird flu with an all-time high of nearly 58 million poultry affected as of January 2023. 

Meanwhile, Europe is in the midst of its worst-ever spate of bird flu infections with 2,500 outbreaks on farms stretching across 37 countries from October 2021-September 2022. Some 50 million birds have been culled across the continent, although the vast majority of poultry infections occurred in France.

More than twelve months since the virus was first detected in late 2021, infections have remained consistently high and show little sign of slowing. In fact, they seem to be gathering pace – European data shows that in autumn 2022 the epidemic was more virulent than the same time the previous year and the number of infected farms 35 percent higher.  

“In terms of the numbers of birds, farms, and countries affected, the number of birds that have been killed and the duration of the outbreak, the current epidemic is truly the largest we've seen in history,” says Ian Brown, chair of the joint World Organisation for Animal Health and Food and Agriculture Organisation of the UN's Scientific Network on Animal Influenza. 

‘Dead birds everywhere’ 

The bird flu virus was first detected among domestic waterfowl in Southern China in 1996. Since then it has re-emerged periodically before naturally petering out ­– or being stamped out through poultry culls ­– even as it expanded its reach into Asia, the Middle East, Europe and North America.  

The H5N1 strain currently circulating originated among wild birds whose migration patterns have accelerated its global propagation. The rate of reproduction is high; one bird is able to infect up to 100 others through saliva and other bodily fluids.  

In Scotland, the coast provides a haven for migratory and sea birds and a crucial habitat for many endangered species. Great skuas currently have a total population of just 16,000, more than half of which inhabit the northwest coast. When numbers of the seabird started to die off in the summer of 2021 it was the first indicator that the H5N1 virus had arrived.  

At the time, authorities thought the summer outbreak was an anomaly. Then in autumn Svalbard Barnacle Geese, which migrate south from their arctic breeding ground, also started dying. “Numbers were going up by 10s, then hundreds, then more that 16,000 were confirmed dead,” says Claire Smith, policy officer for UK bird protection charity the RSPB. By spring, the organisation estimated a third of the total population had died. 

Deaths among great skuas, gannets, gulls, geese and even eagles continued through summer, by then impacting both migratory and domestic species. By July, the Scottish government had closed off access to some seabird islands. “There were just dead birds everywhere,” Smith says.  

Death tolls for this winter have brought little cause for optimism in 2023. On the Island of Islay in particular, Smith says: “We're not at the end of winter yet, but numbers of deaths are already ahead of last year.” 

Although not all wild birds are susceptible to H5N1, many species around the world have suffered similar decimation. Populations of penguins in South Africa, dalmatian pelicans in the Balkans and cranes in Israel have diminished.  

Against a backdrop of environmental threats such as climate change, many may never recover their numbers. “It's not dramatic to say there are some endangered species of wild birds that could become extinct,” Brown says. 

‘Carrying the virus’ 

Among farmed birds there is no threat of extinction, but a global death toll of more than 140 million so far is still cause for deep concern. Aside from the ethical questions raised by such vast loss of life, the result has been loss of income for farmers, and soaring prices for poultry and eggs – both essential sources of affordable protein.

In Europe the response to bird flu outbreaks in the past decade has been surveillance followed by culling to stamp out infection. “You depopulate the farm, disinfect it and put in measures to limit any risk of spread from that farm,” Brown says.  

Farms can also implement biosecurity measures such as good hygiene practices to prevent the virus entering. “But even with good hygiene, this virus could find its way in,” Brown adds. As H5N1 is present in wild birds, one infected animal can easily fly between multiple farms spreading the infection. And the further the virus spreads, the more the infections between species snowball.  

In the UK, birdlife that wouldn’t normally be prone to bird flu, such as barn owls and kestrels, have recently been infected. “The theory," Smith says, "is that lots of big poultry operations have rodents, and the rodents aren't necessarily dying of bird flu but are carrying the virus on their fur, then those barn owls and kestrels are catching them.” 

There are few instances of the current bird flu epidemic spreading to mammals, although examples do exist including cats, pigs and tigers. Human infections are also rare and mild, although a handful of cases have been reported. “At the moment, it does not have a high ability to spread and infect people, but we can't assume that will always be the case,” says Brown. “These viruses change and mutate over time.” 

‘A year-round disease’ 

With no signs of global infections slowing the stakes are rising, especially as there is little hope of respite at the end of the traditional winter flu season. In 2022, “the virus managed to maintain itself, particularly in northern Europe through the summer", says Brown. “That's the first time it's done that – it's become a year-round disease.” 

In addition, this outbreak marks the first time bird flu has been detected in Latin America with outbreaks in Columbia, Peru, Venezuela, Chile, and Ecuador, posing a potential risk to farmed and wild birds including the unique species that inhabit the Galapagos.  

For wild birds, long-term solutions are hard to come by. It would be unethical to cull populations. Possible preventative measures, such as removing infected dead birds from colonies, must be done without disrupting wildlife living in the surrounding habitat.  

The RSPB has called for restrictions on hunting and the release of game birds to preserve birdlife and reduce infection. There are also some potential signs of natural resistance developing. “There are barnacle geese that have come back [to Scotland] this year and haven't got infected raising questions around antibodies and resistance,” Smith says, adding that “there are a lot of species that don't seem to be susceptible". Crows, for instance, seem to be immune even though they scavenge from infected dead birds. 

For some farmed birds in Europe structured intervention is probable: immunity through vaccination would reduce the need for culling and the likelihood of infected poultry going on to infect other bird species. Although it is unlikely every farmed bird would be inoculated, some may get vaccines as soon as summer 2023. “There's been intensive work on vaccine trials and The European Commission has developed a framework on how these vaccines can be delivered with an ambition to be able to roll that out by summer,” Brown says.  

Regular poultry vaccination might become an inevitability, he adds. As human life has been said to be entering an age of pandemics in the wake of Covid, the same is now true for birds. “We are facing a continuous threat that these outbreaks might occur every four or five years,” says Brown. “So, we have to look at interventions and how we control the disease to tip the balance in favour of removing this problem. Vaccination clearly is going to have an important role to play.”