A highly pathogenic avian influenza—more commonly known as bird flu— has been rapidly spreading across the globe and in the past months has finally entered the U.S.
Although risk to humans is low, H5N1 has so far led to U.S. farmers euthanizing more than 37 million poultry in mass culls to prevent the deadly virus from spreading. The toll on wild birds is just as alarming, with infections and deaths documented in over 50 species, including bald eagles and owls.
The way the virus has spread and to such a large variety of birds has been a shock to many in the scientific community.
“An outbreak of this size and scale has never been seen before in North America,” Professor of Biology Nichola Hill says. “We’ve only had two outbreaks and this one has a much bigger geographic range and is impacting a broader diversity of species compared to the last outbreak in 2014-2015.”
Hill, who studies how viruses jump to new species, is the lead author of a study released this week in the journal PLOS Pathogens, which uses historical data to look at how bird flu transmits among different groups of birds, and which birds are super spreaders of the virus. The study findings have the potential to refine and enhance global surveillance of bird flu and outbreak prediction.
“Resources for disease surveillance are limited. We’re in the middle of a pandemic so there’s only so much bandwidth and funding that can go to bird flu versus COVID versus everything else in the world that’s emerging,” Hill said. “We need to be informed and make decisions about when, where and how to target limited resources to get in front of the next emerging virus. … When you have proactive surveillance in place you can say, ‘OK, here and now is where we need to ramp up biosecurity on farms and heightened public awareness of wild bird mortalities.”
Hill said that after the 2014-15 outbreak, which resulted in the death and culling of more than 40 million birds, she knew it was likely a matter of time before this happened again.
Along with colleagues at the Runstadler Lab at Tufts University’s Cummings School of Veterinary Medicine and other experts in the field, Hill began looking at long-term, historical data of 3 different influenza subtypes: HPAI H5, H13, and H16 to find patterns and determine which birds were really driving global spread.
Historically, when scientists talk about bird flu hosts, they categorize them as either ‘wild' or ‘domestic' animals, Hill says. But these categories are too broad and aren’t very informative for predicting how the virus may spread. In her study Hill found that wild birds are not created equal, and key differences exist in terms of how they contribute to virus spread.
“Wild birds are a very diverse group,” she said. “For example, in the U.S. alone there are over 1,000 species. When the virus spreads in a diverse group of hosts like wild birds, it spells trouble and a multitude of different transmission pathways. The differences are actually astonishing, and we overturned a few dogmas in the process.”
Wild ducks have traditionally been considered super-spreaders because they can carry the virus without symptoms, and they swim and fly, contributing to both local and long-distance virus movement. But Hill’s research shows that other birds also play an outsized role in transmitting the virus.
For instance, wild geese, combined with land birds such as raptors and corvids tended to be responsible for spillover into poultry. Hill says we need to understand why in terms of their host pathology, immunity, behavior, and ecology.
“One ecological factor that may play a role is that geese are land grazers and thrive in cities and agricultural settings,” she said. “Many goose species, here and in Europe, are considered pests. They really are the perfect spillover host because they really like human-altered habitat.”
Gulls, also a species happy in human habitat, were rare hosts for HPAI but when they did become infected, they spread the viruses incredibly fast, which has implications for how introductions into new geographic locations occur, such as Trans-Atlantic spread between Europe and the Americas.
Hill said once you know which groups of birds are playing outsized roles in movement and spread of the virus, there’s a lot you can do.
“You can actually make predictions about where it will go, how fast, and what interspecies transmission events we will see,” she said. “There’s so much use in understanding the basic ecology and evolution of wild birds as a way to predict how this virus will move and where it will go next.”
This means collaborating with ornithologists, ecologists and field biologists to understand how birds move and evolve. And there is a financial advantage to doing good data informed surveillance, she said.
“We need to pay attention to this. Early surveillance costs a fraction of what it does when outbreaks get into the poultry sector,” Hill said. “It’s costing millions and shutting down international trade. It’s a huge price tag when the virus makes its way into commercial agriculture. It is such a shame.”
Risk to Humans
Hill says the risk to humans is still low, but worth paying close attention to. When we have seen human cases, they are isolated and the source is typically infected poultry, not another human, she said.
“The big concerns are that adaptation to wild birds means a larger number of transmission pathways are now possible,” Hill said. “This will probably result in more spillover into agricultural animals like poultry and potentially even swine. In the U.S., this spells huge outbreaks, especially given how industrial agriculture concentrates high densities of young animals that are very naive to infection. Where there are outbreaks in poultry or swine, then human infections can follow.”
The U.S. confirmed its first case of human bird flu last month in a Colorado prison inmate who was disposing of infected poultry at a farm that had to cull their flocks.
“We haven’t yet seen community transmission or signs of the virus adapting to efficient transmission in humans. But COVID-19 is a reminder that human food production creates novel pathways for spillover. Two things worry me about bird flu: it is now entrenched in industrial food production systems across the globe and the evolutionary rate of HPAI H5 is orders of magnitude higher compared to coronaviruses.”
Collaborating with Nantucket Field Station
Hill’s research also found that while surveillance efforts have been mainly based in Alaska, or other breeding grounds in temperate regions, it will serve scientists well to build up surveillance in local areas such as Cape Cod in New England.
The latest strain of HPAI was spread through the Atlantic Flyway, via wild birds from Northern Europe. “We believe infected birds touched down in the Canadian maritime provinces and overlapped with birds that migrate south to overwinter in Cape Cod and lower latitudes. So establishing coordinated monitoring along the Pacific and Atlantic makes most sense to achieve early detection,” she said.
Hill has been collaborating with Yvonne Vaillancourt, director of UMass Boston’s Nantucket Field Station, to coordinate testing of birds on Nantucket. Vaillancourt, who sits on Nantucket’s Highly Pathogenic Avian Influenza Task Force, performs sweeps of the beach looking for any birds who may be wobbly, show neurological symptoms, have slack necks, lack of coordination, or a loss of balance.
“It’s been monumental having someone out there being the eyes and ears of this, looking out for bird health in the middle of this outbreak,” Hill said of Vaillancourt and the field station. “There’s no cardinal symptom for bird flu. It is incredibly difficult to diagnose just by looking at a bird. You really need to swab it and do molecular screening which is what my lab does at UMass Boston.”
Hill, who came to UMass Boston in 2021, is excited to collaborate with her fellow faculty members.
“It was amazing to arrive here and connect with faculty who are leading experts in ecology and evolution. I’m looking forward to synergizing with other faculty and coming out with research that is super original and creative on this topic, which is what disease surveillance needs right now—a bit of innovation.”
And there’s a lot to be done.
“We’re concerned about species of high conservation value in Massachusetts, such as Roseate Terns, Common Loons and Piping Plovers. There are worries the virus could devastate regional populations. A lot of reports we’re getting from rehab centers where they get birds get handed in… it’s just heartbreaking. In collaboration with the Runstadler Lab at Tufts University, we’ve seen infected Bald Eagles, Crows, and Sanderlings - these tiny little shorebirds. If you asked me a year ago whether flocks of Sanderlings were susceptible, I would’ve said, ‘There’s no chance. It’s mostly going to stick to ducks and maybe geese and some gulls.’ Now it’s like, ‘Wow, the host range is so much bigger and the spread is advancing much quicker than what we ever imagined.’”Source : umb.edu