We have to consider potentially all species of birds
could have some level of susceptibility, which of course is a new dimension.
Despite surging and cresting in the past year, the now-global strain is showing no signs of burning out. As a result, birds are facing their own pandemic, with unknown long-term consequences for avian health.
Host Range
H5N1 clade 2.3.4.4b has an extensive host range. This list includes almost 500 different bird species globally.
By now, USDA’s National Wildlife Disease Program has detected the virus in nearly 150 avian species, such as Canada Geese, Brown Pelicans, Red-tailed Hawks, and Snowy Owls, and recorded thousands of dead birds, says program lead Julianna Lenoch.
Waterfowl and Seabirds
H5N1 is most commonly detected in aquatic birds. Some species of waterfowl like ducks don't get sick from a H5N1 infection. This is highly problematic as local outbreaks are kept going by this reservoir species. While the high mortality in other species would usually lead to the virus running out of hosts, the virus can sustain itself over a long time without becoming less lethal to many species.
H5N1 strives within the crowded colonies of seabirds. Most reports of H5N1 infections are from coastal regions.
So far this breeding season, the virus has largely impacted further south, devastating breeding colonies of black-headed gulls and terns, with thousands of adults and chicks dying at colonies across England, Wales and Northern Ireland.
HPAI A(H5) or A(H7) virus infections can cause disease that affects multiple internal organs with mortality up to 90% to 100% in chickens, often within 48 hours. However, ducks can be infected without any signs of illness.
Avian influenza A viruses have been isolated from more than 100 different species of wild birds around the world. These viruses occur naturally among wild aquatic birds worldwide and can infect domestic poultry and other bird and animal species. Wild aquatic birds include waterbirds (waterfowl) such as ducks, geese, swans, gulls, and terns, and shorebirds, such as storks, plovers, and sandpipers. Wild aquatic birds, especially dabbling ducks, are considered reservoirs (hosts) for avian influenza A viruses. Wild aquatic birds can be infected with avian influenza A viruses in their intestines and respiratory tract, but some species, such as ducks, may not get sick.
These findings provided insights into how ducks may have evolved immunity to bird flu viruses and also shed light on how birds respond to such infections.
Although further work is required to fully understand the implications of these findings, the knowledge gained from the duck genome sequence may one day provide clues for combating such viruses in humans.
Migrating Birds
Migrating birds are spreading H5N1 all over the globe. With the introduction of H5N1 clade 2.3.4.4b this is happening to an entirely unprecedented extent. H5N1 is now present during all seasons, spreading continuously with an extended host range. Since the detection of H5N1 clade 2.3.4.4b in 2020, it has crossed the Atlantic from Europe to Newfoundland in December 2021. In August 2023 H5N1 was already detected in the most southern part of America, Tierra del Fuego.
Ringed individuals with a European origin have been found on Newfoundland for 5 species which were found to be HPAI-H5-positive between October 2020 and April 2021, such as Barnacle Goose (1), Eurasian Wigeon (5), Great Skua (13), Black-headed Gull (1). These species might be considered to be possible carriers of HPAI H5 virus from Europe in late winter 2020/2021 or early spring 2021 partly or all the way to Newfoundland. However, given the incompleteness of sampling and the possibility of wild birds carrying HPAI virus subclinically, the involvement of other wild bird species in transatlantic virus transport cannot be ruled out.
Carried long distances by migrating waterfowl, gulls, and shorebirds, within months the virus found almost every corner of North America—and eventually South America—until the situation reached “whole new levels of crazy,” Puryear says.
Data reported here, in combination with the recent highly pathogenic AIV findings in Newfoundland, Canada, suggest that wild bird surveillance captured the introduction of a Eurasian-origin highly pathogenic AIV into wild birds by the Atlantic Flyway of the United States. The potential introduction pathway probably includes wild bird migratory routes from northern Europe that overlap Arctic regions of North America and then dispersal farther south into Canada and the United States.
The currently circulating HPAI H5N1 is derived from viruses of the goose/Guangdong/96- (gsGD)-
lineage that were first detected in commercially-farmed geese in China in 1996 and have circulated
and evolved in poultry. Multiple strains of virus within the gsGD lineage spread across east and
southeast Asia in 2003-04, some of which was the result of spread by wild birds (e.g. to Japan and
Republic of Korea). In 2005 the first intercontinental wave of transmission of gsGD viruses occurred
across Eurasia and into Africa and has been followed by multiple waves of intercontinental spread.
Viruses in the gsGD-lineage viruses have evolved into 5th order clades and have formed multiple
genotypes. The A(H5N1) virus that emerged in 2020 belongs to clade
2.3.4.4b and has caused numerous outbreaks in wild birds in Asia and Europe, typically during
autumn and winter, as well as in Africa, but has persisted year-round in wild birds in Europe since
2021. That same year, HPAI H5 spread across the Atlantic Ocean to North America, where it spread rapidly across the continent in 2022 and southwards to Central and South
America
Scavenging Birds
Scavenging provides an opportunity for H5N1 to be transmitted back and forth between mammals and birds. The most worrying virus variant detected so far, although not peer-reviewed, was found in a bird with a preference for scavenging, the Red Tailed Hawk.
The species that scavenges frequently amongst the Buteo hawks is the Red-tailed Hawk. Like other hawks, Red-tailed Hawks are smaller than eagles, so they only usually eat smaller pieces of carrion – typically found along roadsides.
One isolate, A/Red Tailed Hawk/ON/FAV-0473-4/2022, efficiently transmitted by direct contact between ferrets, resulting in lethal outcomes.
It was surprising to observe that the virus characterised in this study, detected in hens, differed from all other HPAI A(H5N1) clade 2.3.4.4b viruses circulating in poultry and in birds by a mutation in the PB2 protein, T271A, which is a marker of virus adaptation to mammalian species; it has previously been shown to be associated with increased polymerase activity in mammalian cells and is present in the 2009 pandemic A(H1N1) virus. It should be noted that this mutation has never been observed in H5Nx viruses of clade 2.3.4.4b collected from birds in Europe since 2020. In contrast, it has been detected in ca 7% of clade 2.3.4.4b viruses identified in mammals in Europe, including the virus responsible for the outbreak on a mink farm in Spain. This molecular finding suggests that virus spread from mammals to birds cannot be excluded.
To determine if raptors survive infections with HP H5N1, raptors from the upper Midwest United States were serologically tested for antibodies to influenza A virus (IAV), H5 and N1. Raptors were sampled at The Raptor Center’s (University of Minnesota) wildlife rehabilitation hospital and at Hawk Ridge Bird Observatory. Samples were tested for IAV antibodies using a commercially available blocking ELISA, with positive samples tested for antibodies to H5 and N1. Antibodies to IAV were detected in 86 individuals representing 7 species. Antibodies to H5 and N1 were detected in 60 individuals representing 6 species. Bald eagles had the highest seroprevalence with 67/97 (69.1%) seropositive for IAV and 52 of these 67 (77.6%) testing positive for antibodies to both H5 and N1. Prevalence of antibodies to IAV observed in this study was higher than reported from raptors sampled in this same region in 2012. The high prevalence of antibodies to H5 and N1 indicates a higher survival rate post-HP H5N1 infection in raptors than previously believed.
Extinction, Survival, and Vaccination
H5N1 is already an ecological disaster. It is clearly threatening the survival of several endangered bird species. But not all infected birds die and the survivors may have gained immunity to the virus. Wildlife conservationists go to great length to protect endangered species, especially the California Condor. But not all birds can be hand-fed and individually vaccinated. And it is entirely unclear when this outbreak may subside on a global scale.
The blue eyes of some seabirds appear to turn black after they have had a bird flu infection.
In 1982, only 22 California Condors were left in the world. With the help of biologists, they now number over 500, with more than half flying free in the wild.
A new vaccine has been granted emergency approval to protect California condors from a deadly strain of avian influenza, federal officials said this week, amid attempts to pull the endangered species back from the brink of extinction.
On March 28, The Peregrine Fund captured a distressed female with an active nest for treatment; she was later confirmed HPAI positive and died. The male diligently continued to incubate the egg; however, there was concern for his health if he continued to stay in the nest cave, which was suspected to be contaminated with HPAI from the female.
The Incident Command decided to attempt collection of the egg to encourage the male to move out of the nest cave. Field crews safely accessed the nest and the egg, which then went to Liberty Wildlife for care and incubation.
Total mortality: 21 condors
We estimate the scale of mortality amongst wild birds is in the millions rather than tens-of-thousands reported, through comparison of notification data to accounts literature. The outbreaks amongst wild birds are causing population and species level concerns which may drive extinctions and jeopardise decades of conservation efforts.
Uncontrolled spread of the virus can be catastrophic to the already endangered bird species globally, leading to the mass extinction of several species (...) High mortality in wild birds due to the virus could lead to significant ecological consequences, including vulnerability of predators and alterations in species composition in affected ecosystems, and therefore a possible impact on biodiversity not just limited to avian species.
More than 40% of all Peruvian pelicans dying over a period of a few weeks in early 2023. (...) Elsewhere, significant population impacts around the world include 17% of sandwich terns dying in Europe in 2022; 40% of south-east European Dalmatian pelicans dying in 2021, and 62% of Caspian terns breeding on Lake Michigan dying in 2022.
Following initial identification of HPAIV in a Barnacle Goose on 8 November 2021, up to 32% of the total Barnacle Goose population may have succumbed to disease by the end of March 2022, along with other wild bird species in the area. (...) Analysis of sera from the following year demonstrated that a high percentage (76%) of returning birds had developed antibodies to H5 AIV. This study demonstrates genetic stability of this strain of HPAIV in wild Anseriformes, and that, at the population scale, whilst there is a significant impact on survival, a high proportion of birds recover following infection. (...) However, when sera were measured against contemporary H5N1 HPAI, only 24% (n = 6) showed cross-reactivity, whilst 44% (n = 11) showed cross-reactivity against H5N8 AIV. Swabs taken recovered no positive signals for viral RNA, whilst no clear signs of infection commonly observed following H5N1 HPAI infection were observed following post-mortem examination.
They are unique and idiosyncratic, both beloved and annoying, with many endangered as well, but New Zealand’s native birds are now under threat from a new enemy: a highly evolved strain of deadly bird flu.
The country is in the second phase of vaccination trials on native birds, with early results suggesting it could be an effective line of defence against the highly pathogenic H5N1 avian flu strain.
The good news is that, in Scotland at least, we are not seeing the large numbers of dead birds around breeding sites that we did last year. This may mean that the remaining birds have gained some level of immunity to the virus.
It would be premature to say this current strain of H5N1 is going to die out any time soon … We are facing an international crisis.
