Last May, as wild birds from around the globe converged on Alaska’s western shores for the summer breeding season, local citizen scientists did, too. Armed with sterile polyester-tipped swabs and screw-top vials, the amateur biologists descended upon dozens of homes belonging to hunters in villages such as Kotlik, Pilot Station, Chefornak, and Eek. In exchange for two shotgun shells each, the hunters allowed them to swab the throats and cloaca—a combined genital, intestinal, and urinary cavity—of birds they had killed: 1,014 wild ducks, geese, and seabirds. A month later, another 114 cackling geese from Alaska’s Anerkochik River received similar treatment from United States Geological Survey scientists, although this time the birds were alive.
These research efforts were aimed at gathering avian influenza viruses for later genetic testing. The Geological Survey scientists wanted to determine whether Alaska had served as a breeding ground for the deadly avian viruses that ravaged domestic poultry populations in late 2014 and 2015, causing the worst avian influenza outbreak in American history and generating enormous economic losses, estimated at $3.3 billion. Like human influenza, avian influenza is highly contagious. There are more than 35 subtypes, named according to their geographic origin and pathogenicity—“low pathogenic” strains, common in wild and domestic birds, rarely produce symptoms or disease while “high pathogenic” strains are typically lethal in poultry and some wild birds, such as hawks and owls; for some reason, they usually do not cause any symptoms or disease in waterfowl (scientists have not yet been able to answer why.)
Increasingly scientists have been venturing to Alaska to locate the origin and destination of dangerous avian influenza viruses that result in pandemics. The Last Frontier is a convergent zone, a stopover point where seasonal migration flyways between winter feeding grounds in the southern hemisphere and summer breeding grounds in the northern hemisphere overlap. (The American Pacific flyway, for example, spans from the tip of South America up to western Alaska, while the Central Pacific flyway runs from New Zealand through the Pacific islands up to Alaska.) That makes migratory birds in Alaska a reservoir for diverse strains of avian flu, researchers say, which has contributed to past pandemics. Characterizing how the virus moves “by hosts within a migratory season,” according to a 2015 study in the Journal of Virology, “is important for implementing effective surveillance strategies.” Studying the birds that converge in Alaska could also help researchers determine whether such an outbreak might happen again.
From May to September, about 200 species of migratory shorebirds and waterfowl, totaling in the tens of millions of birds from six different flyways, flock to Alaska’s some 6,000 miles of coastline, where the birds live in mixed-species colonies of up to 2,000 birds. These colonies share the same habitat, food, and water sources. With so many birds so close together, just a few flu infections can spread widely via bird saliva, nasal secretions, and feces. So it shouldn’t be surprising that what the Geological Survey researchers found in Alaska’s hunting villages this summer suggests that the state was indeed the origin of at least some of the viral material that caused the 2014-2015 epidemic.
The team published their findings in the Virology Journal in late March. The Alaskan waterfowl they swabbed didn’t have any of the lethal strains of avian influenza at the heart of the epidemic (highly pathogenic Eurasian/North American H5N1, North American/Eurasian H5N2, and Eurasian H5N8); but they did carry five mild avian influenza viruses, distinct to Europe and East Asia, sharing, the researchers say, “high nucleotide identity” with those deadly viruses—suggesting that they have a comparatively young most-recent common ancestor.
The researchers believe that these waterfowl picked up the benign strains of Eurasian and North American avian influenza in Alaska, which then combined into lethal strains via genetic mutation in the weeks and months during which they were flying over the Midwest along the American Central flyway, also known as the Mississippi flyway, which runs from Alaska through the Caribbean down to South America. As it happens, the highest concentration of poultry deaths occurred in Minnesota and Iowa, in the Mississippi flyway, where tens of millions of domestic fowl on 187 commercial turkey and egg-laying facilities were euthanized (as per U.S. Department of Agriculture protocol) or died after testing positive for avian influenza.
Such mutations for a flu strain, from low to high pathogenicity, can happen fairly easily once a bird is infected. “Each time a virus infects a new host cell, it might acquire a small genetic change in its protein structure,” says Hon Ip, a U.S. Geological Survey scientist and avian influenza expert based at the National Wildlife Health Center in Madison, Wisconsin, one of the nation’s top wildlife disease research facilities. This is because the flu is an RNA-based virus—as opposed to a DNA-based one—that lacks RNA proofreading enzymes. As a result, the enzymes that copy the viral genome make an error roughly every 10,000 nucleotides, says Ip. “Over time the changes accumulate and a new virus is born.”
Ip and others at the Survey are using the bird data from Alaska to figure out how and why avian influenza viruses undergo changes that cause pandemics, something that seems to be more common when the host is a chicken, turkey, or other domestic fowl, or a wild raptor. These pathogenic viruses tend to originate in Asia, Africa, and the Middle East, according to Survey scientists, because the infected poultry are improperly disposed of, and biosecurity measures at farms, as opposed to more industrial facilities, are generally far weaker. In many parts of rural Asia and other developing regions, for example, poultry are generally kept outdoors where they have direct contact with wild waterfowl, which facilitates the spread of avian influenza and other viruses. Outdoor poultry then spread these highly pathogenic viruses to wild birds, which—being migratory—tend to spread them far and wide around the planet.
However, even if poultry are kept indoors, avian influenza can spread very readily. All it takes is a tiny bit of infected wild bird feces on the bottom of a worker’s boot or a tractor tire to transmit it to an entire flock. “Until disease reservoirs are cleared, there will always be a risk that migrating wild birds will bring lethal avian influenza to Alaska and other viral disease hubs in North America,” says Carol Cardona, an avian health specialist at the University of Minnesota.
“It’s through these hubs, on the wings of migratory birds, that poultry diseases from across the world can share diseases with poultry on farms in the U.S.”
Erica Cirino is a freelance science writer based in New York. She covers wildlife and the environment, and specializes in biology, conservation and policy.
