Mass infections among wild birds pose a major risk to the most vulnerable species, are difficult to contain and increase the chances of the virus spreading among people
And highly infectious and deadly strain of avian flu virus has infected tens of millions of poultry in Europe, Asia, Africa and North America. But scientists are particularly concerned about the unprecedented spread of the virus among wild birds: outbreaks represent a significant risk for the most vulnerable species, are objectively difficult to contain e their spread increases the chances of the virus being transmitted to humans. The analysis was published in Nature in an article that warns of not too much future risks.
The spread among wild birds
Since October 2021 the H5N1 strain caused nearly 3,000 outbreaks in poultry in dozens of countries. More than 77 million birds have been culled to curb the spread of the virus, which almost always causes severe disease or the death of chickens. Another 400,000 wild birds also died in 2,600 outbreaks, double the number reported during the last big wave in 2016-17.
Researchers studying the virus say avian flu appears to spread among wild birds more easily than ever before, making outbreaks difficult to contain. Wild birds with their migrations are a vehicle for transporting the virus around the world and it is thus possible to predict where the virus will spread. It is very likely – scientists say – that Asia and Europe will continue to see major outbreaks, but infections could also creep into continents that are not currently affected such as South America and Australia.
Transmission to humans is very rare
Although humans can also contract the virus, infections are rare. Only two cases have been reported since October, one in the UK and another in the US (both patients had come into contact with poultry). Scientists fear that though the high circulation of the virus among bird populations means greater risks for people. “Avian influenza viruses change slowly over time, but the right mutation could make them more transmissible between people and other species“, he claims Ian Barr, Deputy Director of the World Health Organization (WHO) Influenza Center at the Doherty Institute in Melbourne, Australia. “These viruses are a time bomb” He says. «Occasional infections are not a problem, the real concern is that these viruses register a gradual gain of function», That is, they produce genetic modifications capable of acquiring new functions or enhancing existing ones.
The origin of the virus
The highly pathogenic H5N1 strain emerged in Asia among geese around 1996 and spread to poultry throughout Europe and Africa in the early 2000s. In 2005 the strain caused mass deaths among wild birds, first in ‘East Asia and then Europe. “Since then, the strain has repeatedly infected wild birds in many parts of the world,” he says Andy Ramey, a geneticist-researcher studying wildlife at the US Geological Survey Alaska Science Center in Anchorage. Through repeated spillovers, says Ramey, H5N1 appears to have adapted better to wild birds “And now it’s an emerging wildlife disease.” In 2014, a new, highly pathogenic H5 lineage called 2.3.4.4 emerged, which began to infect wild birds, but was not always fatal. This change created the opportunity for the virus to spread to North America for the first time. The lineage has since dominated outbreaks around the world, including current ones.
The virus affects some wild bird species more severely than others. For example, some mallard ducks show no signs of disease, while the virus killed about 10% of the Barnacle Geese population in the Norwegian archipelago of Svalbard late last year and hundreds of Dalmatian pelicans in Greece earlier this year. year. Wildlife researchers are trying to understand why the virus affects species differently. They are particularly concerned about the impact of the virus on vulnerable bird species with smaller populations or limited geographic areas and also for species that are particularly susceptible to infections, such as whooping cranes and imperatorial geese. Ramey points out that only a small fraction of cases in wild birds are diagnosed and reported. “More monitoring could reveal the true extent of wild bird mortality,” he says.
Monitoring
“Monitoring disease in wild birds is resource-intensive and is particularly challenging due to the size of their populations,” says KeithHamilton of the World Organization for Animal Health and suggests targeted surveillance in areas most likely to encounter the virus, such as breeding grounds or migration routes. “An effective vaccine for poultry could help stem the spread, along with reducing the number of birds in production plants,” he says. Michelle Will, a wild bird virologist at the University of Sydney in Australia. «The poultry industry can also continue to improve biosecurity limiting the entrance to the structures, protecting their water sources and reducing contact between poultry and wild birds ».
Although poultry populations can be culled to stop the spread of highly pathogenic avian flu, the researchers stress that wild birds should not be culled to mitigate outbreaks. “Killing wild birds to prevent further infections would not work due to the huge size and wide range of their populations,” he says Lina Awada, veterinary epidemiologist at the World Organization for Animal Health. “In the same way that we shouldn’t be shooting bats to contain the coronavirus, the solution to avian flu is not trying to kill wild birds,” says Michelle Wille.
June 1, 2022 (change June 1, 2022 | 11:17)
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