A chicken on sale in a market in South Africa – one of many countries where bird flu is killing wild and domestic birds
Kim Ludbrook/EPA-EFE/Shutterstock
The virus behind the largest-ever bird flu outbreak originated in Europe and Africa, suggesting that the epicentre of bird flu viruses has shifted away from Asia and onto other continents.
Since 2021, a subtype of the bird flu virus called H5N1 has infected and killed a record number of both domestic and wild birds across the globe. H5N1 was first detected in China in 1996 and largely stayed in South-East Asia until 2005. That year, outbreaks occurred in birds across Africa, the Middle East and Europe. The H5N1 virus later re-emerged in 2021, affecting birds in North America, Europe, Asia and Africa. It has also spread to some mammals, including a few humans.
“Something is different about the mid-2020 and onward viruses than anything we’ve seen since that 1996 detection,” says Richard Webby at St. Jude Children’s Research Hospital in Tennessee. “So just a huge amount of virus in wild birds, like nothing we’ve seen before.”
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To understand the recent spread of H5N1, Webby and his colleagues analysed bird flu outbreaks that occurred between 2005 and 2022. They collected data on the number and location of confirmed bird flu cases worldwide from the Food and Agriculture Organization of the United Nations and the World Organisation for Animal Health. They also obtained genetic information on bird flu viruses using two public databases.
After examining the genetic data, the team traced the H5N1 virus responsible for the 2021 outbreaks and onward to another subtype of the bird flu virus, named H5N8, which originated in Northern Africa. This virus began circulating in wild European birds in 2019, where it subsequently evolved into the current H5N1 virus. That virus then spread through wild European birds for at least a year before causing widespread outbreaks in domestic and wild birds in many more countries in 2021.
“That signals a major change for this particular virus,” says Webby. “The epicentre of H5 evolution, which has been South-East Asia, is actually now changing.”
This suggests that other countries should increase bird flu surveillance efforts, especially those in Africa, where such infrastructure is lacking, he says.
Careful vigilance is critical for understanding which bird flu viruses are circulating and how they are evolving or migrating, says Seema Lakdawala at Emory University in Georgia. This information can guide vaccine development and efforts to curb bird flu transmission. “By understanding what is out there, we can prepare ourselves,” says Lakdawala.
Bird flu cannot yet transmit between people. Humans contract it only by interacting with an infected animal. Increased surveillance is thus critical for warning people in affected areas about contact with birds and other animals that may be sick with bird flu, like seals, foxes and bears. Each human infection gives the virus an opportunity to evolve mutations that could help it spread in people. “If we can identify places of spillover and reduce spillover in humans, we can reduce the potential for a pandemic emergency,” says Lakdawala.
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