Wild Bird Surveillance: Influenza Movement on Flyways

Conducting influenza surveillance in wild and domestic animal hosts is part of the CEIRR Network’s core mission to study respiratory viruses with pandemic potential. Wild birds, especially shorebirds and waterfowl, represent a significant reservoir of influenza viruses in part due to their migration patterns allowing viruses to spread over large geographic regions quite quickly. Researchers from St. Jude Children’s Research Hospital CEIRR (SJCEIRR), David Stallknecht, Ph.D. and Rebecca Poulson, Ph.D., lead avian influenza surveillance in wild bird populations at the University of Georgia (UGA). The main goals of these efforts aim to understand the 1. ecology and epidemiology of avian influenza viruses in a wide range of avian hosts, 2. viral persistence in wild bird populations, 3. how these viruses move with wild animal hosts, and 4. the significance of highly pathogenic (HP) H5N1 in wild bird populations.

Since 2014, the CEIRR Network (and previous iteration called CEIRS) has sampled nearly 260,000 wild birds for avian influenza viruses. Surveillance efforts cover much of North America with sampling in all four major migratory patterns, called flyways: the Pacific, Central, Mississippi, and Atlantic. These loosely defined and overlapping migratory zones extend well-beyond North America, as well. All four flyways stretch into South America (not shown) where many waterfowl migrate during the North American winters; notably the Atlantic flyway overlaps with flyways in Europe (not shown). The vast geographic area that migratory birds cover highlights the importance of researching the pandemic potential of avian influenza A viruses (IAVs) in spurring the next outbreak. Multiple types of IAVs could be present in a migrating bird population at the same time. Some gene segments of these viruses can mix, often termed viral reassortment, leading to new strains of influenza. Birds traveling with these IAVs can spread the virus to other bird species, or even to land animals and mammals. To understand the impact of avian influenza on wild bird populations, Drs. Stallknecht, Poulson, and others in the field surveilled IAVs in bald eagles, snow geese, mallards, and ruddy turnstones, among other species. In an interview with the iDPCC, Drs. Stallknecht and Poulson shared more about how they got involved in studying avian influenza in wild birds, the importance and impact of their research, and how their work challenges paradigms to expand our understanding of avian influenza dynamics in wild birds.

How Did They Start Studying Influenza in Wild Birds?

Both Dr. Stallknecht and Dr. Poulson are faculty at the Southeastern Cooperative Wildlife Disease Study at the College of Veterinary Medicine at UGA, and both had serendipitous entries into the field of avian influenza in wild birds. Dr. Stallknecht, Professor Emeritus at UGA, started working with flu in the 1980's as a wildlife biologist working on a USDA task force assigned to an outbreak of HP H5N2 in poultry in Pennsylvania. There he met and worked with a renowned avian flu expert from St. Jude Children’s Research Hospital, Robert Webster, Ph.D. This was followed by graduate work on influenza in wild blue-winged teal at Louisiana State University, and he’s been studying influenza ever since, including his involvement in the CEIRR and CEIRS Networks from the beginning.

Dr. Poulson, who’s now an Assistant Professor, began studying influenza after she moved to Georgia. She applied for a research technician role in Dr. Stallknecht’s lab and quickly fell in love with the field, eventually completing her Ph.D. with Dr. Stallknecht. Dr. Poulson loves that the avian influenza field is “so constantly changing and there are so many underexplored and unanswered questions.” Giving a personal reason why she’s stayed in the field, “Ruddy turnstones also, separately, are very charismatic.”

Importance of Wild Avian Surveillance and Research

Drs. Stallknecht and Poulson focus on the future to inform present conservation efforts in wild birds. They value wildlife and aim to keep these natural resources “front and foremost” in their research. Dr. Poulson always advocates for wildlife to be an “equal member at the table” when discussing health: “The health and well-being of these animals and their populations is critically important to entire ecosystems. And sometimes I feel like that gets lost in conversations.” Their group views their research from the wild bird perspective: working to understand the wildlife reservoir, how viruses persist, and when and where they’re capable of entering into that reservoir.

When Drs. Stallknecht and Poulson started detecting infections of a new strain of influenza (HP H5N1) in North American wild birds, they also saw increases in mortality in many wild bird species: eagles, condors, ducks, and more. The fieldwork became emotionally taxing. However, when they began investigating snow geese, and applying antibody tests not normally applied to wild bird surveillance, they found that many infected birds including black vultures, condors, eagles, and even mammals, actually survive infection. This was encouraging to learn and provided much need information to understand possible impacts on wildlife populations.

The iDPCC dove deeper into the health and safety of animal populations to better grasp the risk of influenza transmission from wild birds to mammals. Dr. Stallknecht notes that the risk is nearly impossible to quantify in the wild, but described three major scenarios where avian influenza transmits to another species:

Most wild bird infections are caused by low pathogenic avian influenza (LPAI), which can but rarely pass to wild or domestic mammals. These viruses do “spill over” to domestic poultry on occasion and can cause severe problems.
In contrast, highly pathogenic avian influenza (HPAI) infections have a higher risk to “spill over” into wild mammals because they often kill their bird host. Wild mammals and predatory birds may come across weak or deceased birds and eat the carrion. Direct contact with HPAI is the main factor in determining whether a wild animal will acquire an infection.
With HPAI, infections also have been detected in domestic mammals (cats, dairy cows) but direct transmission from wild birds is rare, and these problems are usually associated with human error, such as not providing an adequate barrier between wild birds and these animals.

Because of the potential death toll and transmission to other species, detecting positive cases of HPAI rings the alarm bells. Their group quickly studies the characteristics of the virus and assesses the risk to wildlife. Unfortunately, this presents a series of challenges. “Basically, we're dealing with a problem right now that we don’t know where it’s going, and we don’t know how bad it will be, and this type of event will happen again, even if we get beyond this one,” explains Dr. Stallknecht. While these viruses of concern present complex issues, Drs. Stallknecht and Poulson focus on understanding the trajectory of the virus and what may be possible, so they can devise strategies to keep wildlife safe and impacts low.

Challenging Paradigms in Shorebird Migration

The paradigm in North America holds that shorebirds migrate from South America in early spring towards their Arctic breeding grounds and stop in Delaware Bay via the Atlantic flyway. The birds fuel up on horseshoe crabs before continuing their journey to the Arctic. This sparked an intuitive site for influenza sampling efforts that are still ongoing by SJCEIRR researchers. The Network has learned a lot about the wildlife and virus dynamics within Delaware Bay over the years. A major problem lies in what happens outside of the bay. Dr. Poulson notes, “It’s hard to pinpoint where the viruses detected at Delaware Bay come from.”

To start teasing apart the inputs of influenza into the Delaware Bay ecosystem, Drs. Stallknecht and Poulson leveraged their proximity to the southeastern US coastlines. They increased sampling on South Carolina, Georgia, and Florida coasts over several years to interrogate shorebird species in different times of year to understand how these viruses are maintained, and then subsequently moved to new locations. Using nano-tag telemetry on ruddy turnstones in the southeast, they tracked virus and bird movement over time and space. They found that many birds stop in the southeast US and can bypass Delaware Bay on their way to the Arctic. They’re starting to tie together movement and maintenance of viruses at different times of year based on genetic similarity. They found genetic similarity of IAV in the southeast during winter and detected similar genetic signatures in IAV at Delaware Bay months later. Dr. Poulson highlights the utility of this “multi-pronged approach [of] linking telemetry, viral movement, and genetic data to better understand the role of shore birds in disseminating viruses to different locations.”

To wrap up our discussion, Dr. Poulson recalls a common phrase in the field: “The more we learn about flu, the less we know.” There are many open questions and challenges when studying wild populations, but Drs. Stallknecht and Poulson’s passion for the health of these ecosystems drives them to maintain their effort. However, they’re not alone in this effort. Dr. Poulson noted, “Lots of dots on that map, right? And lots of collection efforts. But in fact, that is representative of just a handful of dedicated groups historically having collected all those data. That’s a small but mighty and critically important effort.” Drs. Stallknecht and Poulson are proud to belong in the CEIRR Network community for so many years and look forward to researching influenza’s role in these dynamic, wild bird ecosystems.

To read more about this topic, check out:

Wild Bird Surveillance: Influenza Movement on Flyways

Interview with SJCEIRR Experts Dr. David Stallknecht and Dr. Rebecca Poulson