How is bird flu affecting animal populations? – Gavi, the Vaccine Alliance
August 18, 2024
Brown skuas and south polar skuas, two gull-like species that nest in Antarctica, are sometimes called the pirates of the Southern seas. These migratory seabirds are fierce, competitive predators that hunt or scavenge anything, from eggs and adult birds to seafood, mammals or garbage.
Theyre really tough animals and theyre dying, says Antonio Quesada, director of the Spanish Polar Committee.
He gravely recounts why this seasons field work in the Antarctic was like no other: A lethal strain of avian flu, H5N1,breached this fragile ecosystemin February. Only a handful of specially trained researchers were allowed onshore in outbreak sites, garbed in hazmat suits to prevent contagion and spread.
The true scale of the event is still unknown, but reports were grim. In the Falkland Islands, H5N1killed 10,000 black-browed albatrossand ravageda gentoo penguin colony. Scientists discovered a mass skua die-off:50 carcasses littered a Beak Island nesting colony of 130.
Quesada has rarely seen a single dead skua in 20 years work in Antarctica. Theyre an indicator species. If theyre dying, what does it mean for other birds? he asks.
The threat posed by H5N1 extends far beyond the frozen South. Few people realize that the world is currently gripped in another serious pandemic or, to be exact,apanzootic, the animal equivalent. This virus has now infected more than 500 bird and mammal species.
Since it emerged in 2020 in Europe, this Highly Pathogenic Avian Influenza (HPAI) strain has blazed a trail of death across the planet, the largest outbreak in history. The virus is both lethal and unusually transmissible, jumping between birds, mammals and livestock with frightening agility.
Experts say the threat to humans is rising. Manycountries are increasing surveillance and developing or buying vaccines. Cases areticking up in the U.S.: Four people contracted the virus from cows and 10 others caught it from chickens.
Meanwhile, it continues to devastate wildlife, including many endangered animals, saysChris Walzer, executive director of health at the nonprofit Wildlife Conservation Society. As of March, H5N1 had leapt the species barrier to infectsome 485 types of birdandat least 48 mammal species, according to United Nations estimates. Many of these species had never been diagnosed with avian influenza before.
The disease has infiltrated even the most remote regions on six continents. When a polar bear in Alaska succumbed in 2023, it marked the first detected mammal death from avian flu in the Arctic. Thus far, only Australia and the Pacific Islands have been spared. And the virus is still on the move, spreading to new hosts as it evolves and picks up genes from other bird flu strains.
Victims have died in staggering numbers, especially animals that congregate in large groups like pinnipeds. The virus swept along South Americas Atlantic and Pacific coastlines,slaying more than 30,000 sea lionsin 2022-23. It then killed some17,000 Southern elephant seal pups on Argentinas Pennsula Valds the species largest die-off ever.
H5N1 has been carried worldwide by migrating birds. Butnew researchshows that this current strain (dubbed clade 2.3.4.4b) can now spread directly between mammals, with frightening implications. It seems that H5N1 viruses are becoming more evolutionarily flexible and adapting to mammals in new ways, the studys authors write, which could have global consequences for wildlife, humans, and/or livestock.
Walzer warns, H5N1 now presents an existential threat to the worlds biodiversity.
Its important to understand that this panzootic is a man-made problem, says Vincent Munster, who heads the Virus Ecology Section at the U.S. National Institute of Allergy and Infectious Diseases.
Avian flu is not uncommon in wild birds, particularly in its natural hosts:ducks, geese, gulls, terns, swansand other waterfowl. They carry a low pathogenic form, a mild virus that may be asymptomatic. It spreads seasonally, when multiple species congregate at migration stopover sites or cluster together to nest.
But when avian flu spills over into poultry, it can morph into a highly contagious, fatal virus.
The current panzootic began when this H5N1 strain jumped from domestic poultry back into wild birds which happened because of modern livestock production methods. Humans further facilitated spillover by destroying wetlands, which crowds migrating birds into small scraps of habitat, often with poultry farms nearby.
When farms encroach wetlands, it creates the perfect interface for this type of virus, Walzer says. Its a veritable petri dish of opportunity for avian flu to swap genes and mutate into potentially more virulent or transmissible strains. This environment allowed the virus to infect chickens, geese and ducks and jump back into the wild in a virulent form.
The emergence of Highly Pathogenic Avian Influenza is a direct result of commercial, large-scale poultry farming, Munster says. There are more than 34 billion chickens on Earth, according to Food and Agriculture Organization estimates.
The U.S. Delmarva Peninsula offers a prime example of farm-wetland overlap. Its both a migratory stopover and a wintering ground along the North American flyway on the nations Mid-Atlantic coast. Its also the site of a$4.4 billion poultry industry that raised 600 million chickens in 2023. H5N1 has hit there and across the globe. In Cambodia, for example, farmers that raise their ducks and geese in wetlands have also seen outbreaks.
The virus is now spreading among cows, infecting at least171 herds in 13 U.S. states. It thrives in udder cells, and RNA from H5N1 has been found in milk.
Another serious concern: H5N1 has not petered out between spring and fall migrations, like avian flu normally does. Its now endemic in Europe and North America. When that happened, Walzer says, people began worrying that its not going to go away anymore.
It has flared for four years straight now, with wild birds currently carriers, reservoir hosts and victims of the virus.
H5N1 isnt new. In 1996,a goose in Chinas Guangdong province may have been patient zerofor the current strain, which spread among the flock and passed to wild birds. The virus then morphed into asevere respiratory disease that infected 18 people and killed six in Hong Kong. That outbreak ended after 1.5 million chickens were slaughtered.
Next came a viral chatter phase. Viruses dont just break through species barriers. As they change, they make periodic forays into other species, sometimes over years. In most cases, these ventures are unsuccessful. Unless a virus can enter cells and replicate, it circulates harmlessly.
Flu virusesmutate rapidlyas they acquire genes from other viruses: mixing, matching, reassorting and adapting, says Colin Ross Parrish, a virologist at Cornell Universitys College of Veterinary Medicine. Each genetic mutation creates a new building block for evolution: Genetic sequences are cellular instructions. They help a virus evade immunity in a host, determine how it causes infection, how it spreads and much more.
Avian influenzaseight-section genomeoffers numerous opportunities to reassort its genetics, not unlike a Las Vegas slot machine and in 2003, it hit a viral jackpot. Avian flu mutated to successfully spill back from poultry into wild birds,launching the current panzootic.
Fast forward to 2020 when H5N1 appeared in its current form in European birds and then successfully infiltrated new species, including mammals. It quickly spread to Africa and the Middle East, as it was carried long distances along migratory flyways. Humans helped byselling and shipping infected poultryacross national borders.
The virus crossed the Atlantic, reaching U.S. and Canadian shores in late 2021. Soon,mallards and swans were dying in the U.S. Midwest, bald eagles died nationwide,seals perished in Maine, as did bobcats in Wisconsin and raccoons in Washington and Michigan, to name just a few of the many losses.
The virus then aggressively invaded South America, targeting birds and sea mammals.Genetic studies on dead seabirds, a dolphin and a sea lionin Peru shed light on H5N1s movement and adaptations. Researchers discovered that in the U.S., the Eurasian strain added genes; in this form, it expanded its repertoire of hosts and raged like wildfire through large seal and sea lion colonies.
H5N1 finally reached both poles. Outbreaks continue to arise nearly everywhere.
Proximity is a big factor in how viruses spread, as the world learned during the COVID pandemic. Sharing a home or gathering in large groups poses a huge H5N1 risk, says Amandine Gamble, an infectious disease ecology expert at Cornell Universitys College of Veterinary Medicine. To understand where birds go and how they spread H5N1, she is collecting genetic material from various species in the Falkland Islands and outfitting them with tracking devices to follow their movements.
Regardless of the location, the virus triggers a systemic infection in birds. They may become lethargic, sneezing, coughing, gasping for air or experiencing intestinal issues. The virus also invades the brain. Sick birds may become disoriented, uncoordinated, stumbling, swimming or walking in circles, trembling or jerking their necks before keeling over dead. Some suddenly die without showing any sign of illness.Survivors may pass the virus to others.
Mammals experience many of the same symptomsas birds, but postmortems have also revealed pneumonia and bleeding in the heart, liver and other organs. Autopsies of 55 mammals showed that the most commonly afflicted part of the brain was the frontal lobe, which explains the movement and cognitive symptoms.
The genie is out of the bottle, says Waltzer. He emphasizes that the length of the outbreak, as well as the amount of the virus in the environment, is unprecedented. The sheer global distribution of this virus, he notes, is underestimated everywhere as well as the breadth of ecosystems that are being impacted.
Researchers are deeply concerned by the effects of this red-alert virus: High pathogenicity H5N1 is a real, tangible threat to wildlife, of a magnitude and scale never seen before, says Marcela Uhart, who heads the Latin American program at the University of California Davis One Health Institute.
On a United Nations situation update map, swaths of the world seem untouched, but that is likely because some regions have little or no monitoring for avian influenza, Walzer notes. For example, experts suspect there is vast underreporting in Africa. Many countries have slim resources, so pathogen hunters target the deadliest human threats: malaria. Ebola, Lassa fever and other infectious diseases.
Many pathogens, including avian influenza, arezoonotic: They jump between wildlife, livestock and humans. In recent decades, zoonotic diseases haveemerged and spread at accelerating rates. They are frequently fatal and have no cure.
As humanity encroaches on wild areas, people, livestock and wildlife come into into unnatural proximity, exposing all to germs they have no immunity to like avian influenza and leave wild animals with ever-shrinking habitat. Add poaching for the illegal wildlife trade, bushmeat hunting, and rapidly changing climate, and its no surprise that many species are in serious danger of extinction.
H5N1 is the newest threat. The number of different species being infected is quite profound, says Emily Denstedt, a health program adviser with the Wildlife Conservation Society.
Wild birds are among the most affected animals. This is a major change: previous H5N1 strains primarily attacked poultry. At least485 bird species from 25 classifications have been infected, including puffins, pelicans peregrine falcons, owls, toucans, parrots, bald eagles, warblers, finches and many others.
However, seabirds are by far the hardest hit. H5N1 super-spreader events in the U.K. offer sobering examples of the carnage wrought by this virus, though theres no way to accurately count the casualties.
Nesting colonies are now notably emptier in many locations. In Scotland home to 60% of the worlds great skuas breeding numbers have plummetedby three-quarters since 2021. Some 16,000 gannets died and the population in Wales dipped to precarious lows not seen since the 1960s. Rangers discovered more than660 dead Arctic tern chicks in England.
During the spring of 2022 in Africa,thousands of birds perished, particularly along the East Atlantic Flyway migration route in Senegal and The Gambia.Later that year, South Africa lost at least 28 African penguins a tragedy for these endangered birds.
In the U.S., the virus struck Lake Michigans Caspian terns, killing 62%. In early 2023, pelicans littered Peruvian beaches; more than 40% of the population died. At least 20 critically endangered California condors perished in Arizona, endangering their perilous recovery from just 22 birds in 1987.
So far, seals and sea lions are the only mammals dying en masse. However, the sheer number of affected mammals is worrying, ranging from grizzly bears, lions, pika, cougars, cows and dolphins to domestic dogs and cats, racoons, foxes, sea otters and a zoo tiger.Six dead walruses were discovered in Svalbardin 2023, some 965 kilometers (600 miles) from the Arctic Circle.
Uhart explains the broader collateral damage: All species play a role in maintaining healthy ecosystems, and big losses reverberate throughout the entire community. She offers pinnipeds as an example. As top predators, seals, sea lions and walruses keep prey species in check. Without them, previously constrained species multiply, may expand their ranges and displace other animals.
We almost wiped out pinnipeds in the past, hunting them for their fur and their blubber, and they are only now recovering after years of protection, Uhart says. We cant let a disease put them at risk again.
There may be other, less obvious effects on wildlife. Birds that sicken and survive probably wont fledge young, Munster says, and birds that breed in large colonies may not thrive in smaller groups. Walzer notes that we humans and our monitoring systems are really bad at detecting these more subtle decreases in populations, And suddenly, theyre gone.
The ultimate extent of this global animal apocalypse will hinge on H5N1s vigor, endurance and adaptability and importantly, on preciselyhowit adapts.
Much depends on the ways species interact. Lifestyle impacts the dynamics of how [H5N1] spreads in animal populations, says Cornells Gamble. In close quarters, it passes between birds, but not all develop terrible disease. They may become silent spreaders.
Another important factor is how animals are exposed and where. H5N1 is a resilient organism: It replicates in the respiratory tracts of mammals and birds and in birds intestines. Animals can shed virus from infected cells after only six hours.
Its quite hardy and remains infectious in water.One study found that H5N1survived in bird fecesfor nearly a day in extreme heat (42 Celsius, 107 Fahrenheit), five days in balmy temperatures (24C, 75F) and for up to two months in the cold (4C, 39F). This strains resilience is still unknown.
Carnivores and scavengers can catch the virus by eating an infected bird carcass. But researchers have also confirmed that mammals now transmit the virus between themselves, in the wild, on farms and in zoos. It spread on amink fur farm in Spain(where tens of thousands lived in about 30 barns), among dairy cows in the U.S.,tigers in a Chinese zooand pinnipeds in Argentina. Scientists determined that the strain that killed elephant seals also infected terns which could spread it far and wide.
Quesada is deeply concerned about the coming breeding season in the Antarctic. Confirmation of the virus in elephant seals puts us on even higher alert, he says.
Risk to humans grows as the virus racks up an ever-longer list of mammal hosts. Fourteen people have been diagnosed this year in the U.S.; all worked with cattle or chickens. So far, theres no evidence that the virus can pass directly between humans. However, the World Health Organization (WHO) has cautioned public health officials to get ready for a potential spillover. Alert levels will jump if H5N1 becomes airborne, if it can be sneezed out and carried via aerosols or respiratory droplets, Uhart says.
A key question remains: As individuals develop immunity, will the virus fizzle out? And if so, when?
Predictions for wildlife arent good. In places where H5N1 has already invaded, Uhart says, it will take years, maybe decades or more, for some wild species to recover. In those locations, she says she believes it will likely remain, continue to adapt and evolve into new strains. She expects recurring deadly waves and for some species that are currently endangered, just one outbreak may mean extinction.
Munster likens this panzootic to the SARS pandemic but in wildlife, with no preemptive, therapeutic or prophylactic countermeasures, like social distancing, masking, vaccines and antivirals.
One strategy, vaccinating poultry against avian flu, could stop or limit the current H5N1 evolutionary pool, Walzer says.
For decades,experts have been waving a red flag, trying to gain traction for aOne Health strategy to prevent future pandemics. Its a holistic approach, inclusive of human, wildlife, livestock and ecosystem health. Importantly, it incorporates disease risk into decision-making. A One Health approachshifts the onus on officials to prevent diseasesbeforethey jump between species, rather than the current model reacting once a crisis hits. Studies show this to be themost effective and economicalpandemic strategy.
In December 2021, amid COVIDs mass human mortalities, the WHO and representatives from 194 nations agreed to negotiate a pandemic treaty. But countries have not yet reached an agreement, missing a May deadline to deliver the document at the 77thWorld Health Assembly.A recent editorialstated that negotiators are nowhere close to adopting text that will truly prevent consequential pathogen spillovers from wildlife.
With massive industrial livestock operations located within migratory flyways, We could have seen [this panzootic] coming, but our ability to actually intervene on a legislative and political level is not there unfortunately, Munster says. And [wildlife] is definitely paying the price.
Meanwhile, viral chatter continues to surge, invisible and unabated between domestic and wild species.
Citations:
Bouvier, N. and Palese, P. (2008). The biology of influenza viruses.Vaccine.https://doi.org/10.1016/j.vaccine.2008.07.039Campagna, C., et al. (2023). Catastrophic mortality of southern elephant seals caused by H5N1 avian influenza.Marine Mammals Science.https://doi.org/10.1111/mms.13101
Uhart, M., et al. (2024). Massive outbreak of Influenza A H5N1 in elephant seals at Pennsula Valds, Argentina: increased evidence for mammal-to-mammal transmission.bioRxiv. https://doi.org/10.1101/2024.05.31.596774
Evseev, D., Magor, K. E. (2019). Innate Immune Responses to Avian Influenza Viruses in Ducks and Chickens.MDPI.https://www.mdpi.com/2306-7381/6/1/5
Chen, H. (2009). H5N1 avian influenza in China.Science China Life Sciences. https://doi.org/10.1007/s11427-009-0068-6
Lycett, S, Duchatel, F. and Digard, P. (2019). A brief history of bird flu. Philosophical Transactions of the Royal Society B.https://doi.org/10.1098/rstb.2018.0257
Harvey, J., Mullinax, J., Runge, M., and Prosser, D. (2023). The changing dynamics of highly pathogenic avian influenza H5N1: Next steps for management & science in North America.Biological Conservation.https://doi.org/10.1016/j.biocon.2023.110041
Kilpatrick, A. Chmura, A., Gibbons, D., Fleischer, R., Marra, P. and Daszak, P. (2006). Predicting the global spread of H5N1 avian influenza.Proceedings of the National Academy of Sciences.https://doi.org/10.1073/pnas.060922710
Leguia, M., Garcia-Glaessner, A., Muoz-Saavedra, B., Juarez, D., Barrera, P., Calvo-Mac, C., Lescano, J. (2023). Highly pathogenic avian influenza A (H5N1) in marine mammals and seabirds in Peru.Nature Communications,14(1). doi:10.1038/s41467-023-41182-0
Duriez, O., Sassi, Y., Le Gall-Ladevze, C., Giraud, L., Straughan, R., Dauvern, L., Le Loch, G. (2023). Highly pathogenic avian influenza affects vultures movements and breeding output.Current Biology,33(17), 3766-3774.e3. doi:10.1016/j.cub.2023.07.061
Rohr, J. R., Barrett, C. B., Civitello, D. J., Craft, M. E., Delius, B., DeLeo, G. A., Tilman, D. (2019). Emerging human infectious diseases and the links to global food production.Nature Sustainability,2(6), 445-456. doi:10.1038/s41893-019-0293-3
Kurmi, B., Murugkar, H. V., Nagarajan, S., Tosh, C., Dubey, S. C., & Kumar, M. (2013). Survivability of highly pathogenic avian influenza H5N1 virus in poultry faeces at different temperatures.Indian Journal of Virology,24(2), 272-277. doi:10.1007/s13337-013-0135-2
Hu, T., Zhao, H., Zhang, Y., Zhang, W., Kong, Q., Zhang, Z., Zhang, F. (2016). Fatal influenza A (H5N1) virus infection in zoo-housed tigers in Yunnan province, China.Scientific Reports,6(1). doi:10.1038/srep25845
Bernstein, A. S., Ando, A. W., Loch-Temzelides, T., Vale, M. M., Li, B. V., Li, H., Dobson, A. P. (2022). The costs and benefits of primary prevention of zoonotic pandemics.Science Advances,8(5). doi:10.1126/sciadv.abl4183
Excerpt from:
How is bird flu affecting animal populations? - Gavi, the Vaccine Alliance
