Avian influenza (AI), known in its early days as chicken sickness, is reported to have first appeared in Italy in 1878. Waterfowl is the natural host of avian influenza virus. Some subtypes of avian influenza virus can not only cause disease in poultry, but also cause illness and even death in human, seriously endangering public health.
Nature news published an article entitled “Why unprecedented bird Flu sweeping the World Are concerning Scientists” on May 26, 2022. It says a highly contagious and deadly strain of bird flu has infected tens of millions of birds in Europe, Asia, Africa and North America. Scientists are particularly concerned that the outbreak, unprecedented in wild birds, poses a significant risk to vulnerable species, is difficult to control and increases the chances of the virus spreading to humans.
Popular status quo
The H5N1 strain has caused nearly 3,000 outbreaks in poultry in dozens of countries since October. More than 77 million birds have been culled to curb the spread of the virus. Bird flu viruses almost always cause severe illness or death in flocks of chickens.
Researchers say the virus appears to be spreading more easily than ever among wild birds, making the outbreak especially difficult to contain. Wild birds help spread the virus around the world, and their migration patterns determine when and where it will next spread. Large outbreaks are likely to continue in Asia and Europe, and infections could spread to currently unaffected continents such as South America and Australia.
Although people can get infected with the virus, it is rare. Only two cases have been reported since October, one each in the UK and the US. But scientists are concerned that the high level of transmission among birds means more opportunities for the virus to spill over to humans.
Ian Barr, deputy director of the WHO Collaborating Centre for Influenza at the Doherty Institute in Melbourne, Australia, said bird flu viruses change slowly over time, but the right mutations could make them more infectious in people and other species. “These viruses are ticking time bombs,” he says. “The occasional infection is not a problem – the real concern is that these viruses are becoming more functional.”
Origin of the virus
The highly pathogenic H5N1 strain emerged in commercial geese in Asia around 1996 and began spreading in poultry in Europe and Africa in the early 2000s. By 2005, H5N1 was killing large numbers of wild birds, first in East Asia and then in Europe. Since then, the strain has repeatedly infected wild birds in many parts of the world, and Andy Ramey, a research wildlife geneticist at the USGS Research Center in Alaska, says H5N1 appears to have become more adaptable to wild birds after repeated spills and is now an emerging wildlife disease.
In 2014, a new highly pathogenic clade of H5, 2.3.4.4, emerged and began infecting wild birds without killing them. That brought the virus to North America for the first time. This branch has since become the dominant pandemic strain in global outbreaks, including the current one.
The virus affects some wild birds more severely than others. For example, some infected mallard ducks have shown no signs of the disease, but the virus killed about 10 percent of breeding geese in Norway’s Svalbard archipelago last year and hundreds of Dalmatian pelicans in Greece earlier this year. Wildlife researchers are trying to understand why the virus affects species differently.
Ramey says they are particularly concerned about the virus’s impact on vulnerable bird species with small populations or limited geographical ranges, as well as species that are particularly susceptible, such as whooping cranes and king geese. Only a small fraction of cases in wild birds are diagnosed and reported, Ramey added, and more monitoring could reveal the true scale of the deaths in wild birds.
Transmission control
Better surveillance of infected wild birds could also help to alert poultry facilities to the risk of future outbreaks, says Keith Hamilton, head of oIE’s preparedness and recovery unit. Areas with large poultry or migratory bird populations, however well monitored, are at high risk of further outbreaks.
Tracking disease among wild birds is resource-intensive and challenging due to their large numbers, Hamilto said. He recommends targeted surveillance in areas where the virus is more likely to be encountered, such as endemic flight paths or breeding grounds.
Wille, a wild bird virologist at the University of Sydney in Australia, says an effective vaccine for poultry could help curb the spread of bird flu while reducing the number of birds in production facilities. The poultry industry can also continue to improve biosafety by limiting access to facilities, protecting their water sources, and reducing contact between poultry and wild birds.
Although poultry can be culled to stop the spread of hPAI, the researchers stressed that wild birds should not be harmed to mitigate the outbreak. Lina Awada, a veterinary epidemiologist at the World Organisation for Animal Health, said killing wild birds to prevent further infections would not work because their populations are large and widespread. This could even make the situation worse, as it disrupts the activities and behaviour of wild birds, helping the virus spread further.
“Just like we shouldn’t shoot bats because of coronavirus, the answer to this problem is not to try to kill wild birds,” Wille said. Collaboration between public health researchers and animal health organizations is also key to the timely detection of spills to the population. “If we can control it in poultry, we can control it in humans, and we can control it in wild birds,” Wille said.