Since October 2021, the H5N1 bird flu strain has caused around 3000 outbreaks in poultry in dozens of countries. More than 77 million birds have been culled to contain the spread of the virus, which almost always leads to serious illness or death in chickens. Another 400,000 wild birds have died in 2,600 confirmed outbreaks :– twice as many as in the last big wave in 2016/17.
According to researchers, the virus in wild birds seems to spread more easily than ever, which makes it particularly difficult to contain outbreaks. Wild birds contribute to transporting the virus around the world, with their migration patterns determining when and where it will spread next. In Asia and Europe, there will probably be major outbreaks, and infections could spread to continents that have not yet been affected, such as South America and Australia.
Although people can be infected with the virus, infections are rather rare. Only two cases have been reported since October, each in the United Kingdom and one in the United States. However, scientists are concerned that the high quantities of virus that circulate in bird populations increase the risk of transmission to humans. Bird flu viruses change slowly over time, but the right mutation could make it transferable for humans and other species, says Ian Barr, deputy director of the influenza center at the Doherty Institute in Melbourne: »These viruses are like ticking time bombs. Occasional infections are not a problem - the real danger is that this virus gradually becomes more functional in humans.
Origin of the virus
The highly pathogenic H5N1 strain appeared around 1996 in Asia with commercially used geese and spread under poultry in the early 2000s in Europe and Africa. Until 2005, the trunk caused mass extinction in wild birds, initially in East Asia and then in Europe. Since then, the tribe has repeatedly infected wild birds in many parts of the world, says Andy Ramey, a research geneticist for wild animals at the US Geological Survey Alaska Science Center in Anchorage. According to Ramey, repeated transmissions seem to have better adapted to wild birds. "It has now become a new wildlife disease," he says.
In 2014, a new highly pathogenic H5 line with the designation 2.3.4.4 appeared and began to infect wild birds without always killing them. This allowed the virus to spread in North America for the first time. Since then, this line has dominated outbreaks all over the world, including the current ones. Europe experienced the most violent outbreak of the disease to date.
Some wild bird species are more affected by the virus than others. Some infected floors (Anas Platyrhynchos) show no signs of illness, while the virus killed about ten percent of the breeding population of nuns (Branta Leucopsis) on the Norwegian archipelago in Spitzbergen and in early 2022 hundreds of frizzy pelicans (Pelecanus Crispus) in Greece. Thousands of gray cranes died in Israel. Wildlife researchers try to understand why the virus attacks the different species differently. They are particularly concerned about the effects of the virus on endangered bird species with smaller populations or limited geographical distribution areas as well as in species that are particularly susceptible to infections, such as screaming cranes (grus Americana) and emperor (Anser Canagicus).
Ramey adds that only a fraction of the cases are diagnosed and reported in wild birds. Increased surveillance could reveal the true extent of mortality in wild birds, he says.
Containment of the spread
Better monitoring of infected wild birds could also help to warn poultry farms of the risk of future epidemics – although there is a high risk of further outbreaks in regions with large poultry or migratory bird populations, no matter how good the monitoring is, says Keith Hamilton, head of the preparedness and resilience department at the World Organization for Animal Health.
The persecution of diseases in wild birds is time -consuming and expensive and a challenge because of the size of their populations, says Hamilton. He proposes targeted surveillance in areas in which an occurrence of the virus is more likely, for example on popular pull routes or breeding areas.
An effective vaccine for poultry could also help to contain the spread, as well as the reduction in the number of birds in production facilities, says Michelle Wille, a wild bird virologist at the University of Sydney. The poultry industry can also further improve security by restricting access to the systems, protecting its water sources and reducing the contact between poultry and wild birds.
Although poultry stocks can be crumpled to stop the expansion of the plague, researchers emphasize that wild birds should not be damaged in order to contain outbursts. The killing of wild birds to prevent additional infections would not work due to the enormous size and widespread use of their populations, says Lina Awada, veterinary epidemiologist at the world organization for animal health. It could even worsen the situation because it would disturb the movements and behavior of wild birds and thus promote the further spread of the virus, she says.
"Just as we should not shoot bats because of the coronavirus, the solution is not to kill wild birds," says Wille. According to the researchers, a holistic approach is needed that takes into account how avian influenza spreads through wild birds, poultry and humans. Collaboration between public health researchers and animal health groups is crucial to detect human-on-human encroachment. "If we get the bird flu under control in poultry, we will control it in humans, and probably we will also contain it in wild birds," says Wille.
© Springer Nature 10.1038/D41586-022-01338-2, 2022
