People are catching avian flu from wild birds, study suggests

Avian influenza may be jumping to people directly from migratory birds as they travel thousands of miles across the globe’s flyways, scientists have warned.

It has long been known that these birds carry H5 viruses, which can then spread into other animals like farmed poultry and even mammals. But humans may also be at risk, research in Nature Communications suggests. 

“Previously, it’s really been thought that the spread comes from wild birds into poultry, then to humans,” said Hannah Klim, a PhD student at the University of Oxford’s Centre for Human genetics, who led the research.

“But our work suggests there’s also direct spread from wild birds into humans. This isn’t a [spillover route] that’s talked about much, but it suggests we need to increase surveillance in the key risk areas,” she told the Telegraph. “As far as we know, this is the first study linking the movements of these migratory birds to possible H5 spillover into humans.” 

The research found one per cent of 2,000 people sampled in Malaysian Borneo’s Sabeh state had been exposed to H5 viruses. When scientists mapped these infections, they noticed that those affected lived within 10km of stopover areas, where migratory shorebirds pause for a rest as they travel through the East-Asian Australasian flyway from Russia to Australia. 

The area encompasses routes used by more than 50 million migratory waterbirds every year. Malaysia is home to 13 important stopover sites for 20 species of migratory shorebirds - including sandpipers, sandplovers and curlews. Four of these rest sites are in Sabah.

“Malaysian Borneo [is] really an interesting place, because it connects a migratory route that goes across some of the most populous regions in the world,” said Ms Klim. “It just goes to show that when we’ve got these sites going through key populous areas, we need to really consider if potential transmission is possible there.”

The research was based on blood samples collected in 2015 in Sabeh state, where highly pathogenic avian influenza has been previously detected in poultry and migratory birds, but never in people. 

Using new analytical tools, the scientists found that people sampled already had antibodies that reacted to H5 bird flu viruses, indicating a prior infection. The findings, they said, demonstrate the importance of ramping up disease surveillance in communities close to stopover sites used by migratory birds – who have not been regularly monitored in the past.

“We probably see one per cent of spillover events that occur,” said Prof Miles Carroll, head of the High Consequences Emerging Viruses Group at the University of Oxford’s Pandemic Sciences Institute, and a co-author of the paper.

“When you start looking at… serum bank samples, you start seeing signals – in this case H5 – of things that we’ve never noticed before, either because they were asymptomatic cases or they didn’t get access to the right care and diagnostics. So I think [this research] just adds to the theory that we only see a tiny speck of what is really going on yearly, weekly, daily.”

But Prof Marion Koopmans, a virologist at Erasmus MC in Rotterdam, said the conclusions that migrating birds transmitted H5 to people in Borneo may be “premature”.

“Interesting work, but a key factor that is missing is whether there was any circulation of H5 among poultry around these people. Not having reports does not mean much, avian flu may go undetected in many settings,” she told the Telegraph. 

Ms Klim said that the team had considered this, but concluded through spatial distributions, modelling and experimental data that wild birds were more likely the source of the spillover. This included analysis showing that H5 antibodies were higher among individuals living in areas close to wild birds, rather than among poultry owners. 

The research comes amid mounting unease about the trajectory of bird flu. Over the last few years the virus has been spotted in more and more mammals, providing additional opportunities for it to evolve to better infect humans.

But more recently, an outbreak in cattle in the United States has triggered alarm – to date, 306 herds in 14 states have reported H5N1 outbreaks. Yet 25 people have also contracted the disease, generally dairy farm workers, including 11 in California and 10 in Colorado.

“Even before this, we knew that H5 is something that’s on the rise globally, and that there’s this huge threat of a potential pandemic,” said Ms Klim. But she added that the Nature Communications paper is an important reminder that while the people most at risk may be those in close contact with poultry, they are not the only ones. 

“We feel that this is an important finding as part of the ongoing conversation around avian influenza,” she said.

The paper also warned that the threat of spillover from migratory birds may be increasing in Borneo, because the habitat of migratory shorebirds is being destroyed due to rising sea levels and land use changes. 

There is an “urgent need” to better understand how these trends “may force zoonotic reservoirs including migratory wild shorebirds into closer contact with humans,” the researchers wrote. 

“This study is one of many that consistently show we’re seeing exposure [to viruses] near these interfaces between human populations and wildlife,” said Dr Kimberly Fornace, an epidemiologist based at the National University of Singapore, and co-author of the report. “So it’s really important to understand how we’re developing land, and how that’s creating new interfaces.”

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