Exclusive: Bird flu surge a threat to human health, experts warn

The incidence of bird flu is spreading rapidly across the globe, posing a major threat to human health, new data has found. 

According to figures from the World Organisation for Animal Health (OIE), shared exclusively with The Telegraph, a record-breaking 14 million avian influenza cases were detected in 2021 – more than in the previous five years combined. 

In total 61.4 million birds died either from the virus or because they were culled to halt its spread.

This represents a 462 per cent rise in cases and a 150 per cent surge in deaths compared to 2020, and follows a bumpy but general trend of increasing infections since records began in 2005 (see chart below). 

Scientists say the skyrocketing incidence of avian influenza – which does not appear to be a consequence of better detection systems – could spell trouble for human health, by generating billions more opportunities for the pathogen to jump to and circulate in people. Since 2005, there have been roughly 2,500 human infections. 

“An increase in poultry outbreaks inevitably brings the virus into closer and more frequent proximity to humans, which is always a risk with viruses like influenza that can rapidly evolve,” Dr Holly Shelton, head of the Influenza Viruses Group at The Pirbright Institute, told The Telegraph. “[This] is a risk that needs to be mitigated against.”

Dr John McCauley, director of the Worldwide Influenza Centre at the Francis Crick Institute, added: “The most important question is… [whether] more cases [means] it is more likely to infect humans. The answer must be yes.”

Between 2005 and 2009, there were 2.6 million bird flu infections reported to the OIE. This rose to 5 million between 2010 and 2015, and 11.9 million in the subsequent five years – but in 2020 and 2021 alone, more than 16.5m infections were reported across the globe (see chart below). 

The UK is among those facing record-breaking epidemics, with George Eustice, the environment minister, warning in December that the country was in the midst of  its “largest ever outbreak”. At least half a million birds have been culled as a result. 

But while experts are concerned that the risk of a spillover event is escalating, they stress that cases of bird flu jumping to people currently remain rare and are generally confined to those who work in close contact with poultry. 

Between 2005 and 2020, when a total of 246 million birds were culled, fewer than 2,500 human cases of various flu subtypes were recorded, and there is not yet any evidence of human-to-human transmission, said the OIE. 

However, last month a duck expert, Alan Gosling, was identified as the first person in the UK to be infected with the deadly H5NI bird flu strain. Meanwhile, four new cases of H5N6 have been detected in China this year – while 67 cases of this subtype have been identified in people since 2014, more than half of all human infections were in the last six months.

Scientists agree that although detection systems have improved, especially in lower income countries, the scale of the rise in cases in birds means it is unlikely to reflect better surveillance – especially in poultry, where disease has always been closely tracked. 

But it is not clear what has driven the surge – a more transmissible strain, shifting migration patterns, climate change or an unexpected “influenza epizootic” have all been discussed.

“I think we are doing better with surveillance but in reality that will only translate into increased observations in wild birds and would not account for the increase in poultry, so… I think this is a real rise in infections, both in poultry and wild birds,” said Dr Shelton.

“There are genetic changes from the H5N8 virus that was predominant in the 2020/2021 season in Europe, whether this translates into the virus is more transmissible in birds has not been experimentally tested,” she added.

“However the number of outbreaks does seem to suggest that either there are higher levels of infection in wild bird populations or that it transmits to poultry more easily… and has been no evidence of human-to-human spread or genetic signatures in the viruses that suggest human adaptation”. 

Dr McCauley also said that “viruses change and ‘fitter’ viruses will spread better until the population builds up immunity”. He added that while avian influenza can spread like wildfire through a battery farm, free-roaming poultry may have more contact with infected wild birds. 

There is a consensus, however, that stemming the transmission of bird flu, introducing strict infection control measures and maintaining widespread surveillance networks will be key to mitigate the risk of new spillover events. 

“Controlling the disease in the animal source is critical to decrease risk to humans,” said Tarik Jasarevic, a WHO spokesperson. “Ongoing circulation of some avian influenza viruses in poultry, such as A(H5) viruses, are of public health concern.

“These viruses can infect humans and the viruses have the potential to mutate to increase transmissibility among humans resulting in an influenza pandemic. 

“To minimise public health risk, quality surveillance in both animal and human populations, thorough investigation of every human infection with a zoonotic virus  and risk-based pandemic planning are essential,” he said.

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