Swab samples collected from waterfowl allowed biologists to determine the presence of avian influenza in positive birds. Photo by Kelsey Weir, USDA

August 1, 2023

Highly Pathogenic Avian Influenza: Locally and Abroad

Map by USDA showing the total wild birds samples by state in the United States from May 2022 to present. Alaska, California, Texas and Oregon sampled the most birds for avian influenza.
State totals of wild birds sampled in the United States for avian influenza since May 2022. Graphic by USDA.

Avian influenza, or the bird flu, as it has come to be known, has been wreaking havoc both in wild birds and domestic poultry across all four migratory bird migration flyways in North America since early 2022. This influenza A virus has behaved differently than most every other strain that has appeared in North America before, causing significantly more mortality across far more avian species. Here, we will detail the spread of this virus locally and nationally, and what is being done by the agencies tasked with tracking and responding to this devastating disease.

What is Avian Influenza?

Avian influenza is classified into two different groups, Low Pathogenicity (LPAI) or Highly Pathogenic (HPAI), where pathogenic refers to the pathogens ability to cause disease. This virus is also classified by the assortment of the two proteins that make up this virus, an “H” protein, of which there are 16 variations, and an “N” protein, of which there are 9 variations. HPAI occurs in only the H5 and H7 groups of these combinations, and the current strain circulating is H5N1. LPAI is present in North America at any given time and circulates throughout wild waterfowl and shorebirds.

Birds infected with LPAI are most commonly asymptomatic, showing no clinical signs of disease. On the other hand, HPAI is defined by its ability to cause disease in domestic poultry, and can have devastating effects ranging from lethargy, depression, diarrhea, loss of motor skills and sudden death.

Hundreds of snow geese rest and feed in a grass field. These are medium-sized, white geese with gray wing tips and pinkish-orange bills. When flocked together like this, geese are more suseptible to avian influenza.
Large numbers of birds congregated together, like these snow geese, are highly susceptible to diseases such as avian influenza. Photo by Veronika Andrews from Pixabay.

Avian influenza viruses, or AIV’s, are transmitted via the fecal/oral transmission route, meaning the virus is passed from one bird to the next via saliva or droppings (think hundreds or thousands of birds feeding and defecating in the same body of water, or sharing a roost site). This allows the virus to spread easily across the migration routes of wild birds. Moreover, HPAI is able to persist for days or even months within the environment outside of the host, given the right temperature and other environmental factors. This environmental persistence means that mechanical transmission (e.g., physically being moved by vehicle tires, footwear, carried by pets or wild animals, etc.) becomes another way the virus can move and infect domestic poultry.

Behavior of the Current HPAI Outbreak

In previous North American HPAI outbreaks, such as in 2015-2016, wild birds were mostly asymptomatic and played a role in the transmission of the virus to domestic poultry, where devastating effects occurred. This current strain, however, is behaving differently, causing widespread mortality ranging from isolated instances within raptor species, all the way up to large scale die-offs of migratory waterfowl. Illinois has experienced multiple large, wild bird mortality events, involving double-crested cormorants, lesser snow geese and Ross’s geese, with the events ranging geographically from Cook County to Perry County. HPAI has also been detected in other species in Illinois, including Canada geese, mallards, peregrine falcons, red-tailed hawks, great horned owls, bald eagles, turkey vultures, blue- and green-winged teal, ring-necked ducks and American white pelicans. As of May 2023, there have been more than 6,525 detections in wild birds in 49 states, with 84 of these detections occurring in Illinois.

A map produced by USDA that shows the number of positive wild bird samples with avian influenza in the United States. Florida had the most with 417 detections and West Virginia had the least detections with only one case.
State totals of the number of wild birds detected positive for avian influenza. Graphic by USDA.

As this virus has continued to spread in birds, and mortalities occurred more frequently, state and federal agencies began detecting HPAI in mammals showing neurological symptoms or mortality. These are almost always single, isolated events, where a mammal most likely scavenged on a bird that had succumbed to HPAI and was essentially inoculated or received a direct heavy viral load by ingesting this infected individual. Infected mammals have included red fox, bobcat, striped skunk, raccoon, coyote, mountain lion, river otter, and, here in Illinois, a Virginia opossum. There has been no evidence of transmission between mammals.

To date, this virus has infected 819 poultry flocks, including commercial and backyard operations, in a total of 47 states. A staggering 58.65 million birds have been lost to HPAI, making this the deadliest foreign animal disease to date on North American soil. Severe economic effects have been felt by the high prices inflicted upon poultry products as a direct result of this pathogen.

Assessing Wild Birds for Avian Influenza

With what appears to be a dreary forecast in nationwide avian health, you may be asking, “what is being done to stay on top of this virus as it spreads across the country (and the world)?” The United States Department of Agriculture’s Animal and Plant Health Inspection Service’s Wildlife Services program is one of the federal agencies tasked with the responsibility of answering the questions related to who, what, when, and where, as it relates to HPAI in wild birds. This process is achieved through systematic sampling throughout the states, which means wildlife disease biologists and other Wildlife Services personnel are out in the field taking swabs from wild birds.

A researcher examines a harvested duck  in the back of a pickup truck. Swab samples were taken to test for avian influenza.
Many of the waterfowl swab samples tested for avian influenza were thanks to the cooperation of waterfowl hunters who allowed sampling of harvested birds at public boat launches during open waterfowl seasons. Photo by Mitch Oswald, USDA WS.

Somewhat similar to Coronavirus testing in humans, biologists collect swabs from birds to detect the virus, one from the throat and one from the cloaca (the orifice that birds use for both waste elimination and copulation). To get these samples, Wildlife Services staff relies heavily on the cooperation of waterfowl hunters to allow sampling of harvested birds at public boat launches during open waterfowl seasons, as well as Illinois Department of Natural Resources’ (IDNR) wildlife biologist when they are capturing and banding ducks. Additionally, Wildlife Services biologists will trap, band, sample and release target waterfowl species in some areas. Through this process, Wildlife Services can be aware and alert IDNR biologists where the virus is present, if it’s circulating through certain species or age classes of species, and whether these are isolated or widespread events. The public also plays a critical role in HPAI surveillance by reporting mortality events to either Wildlife Services or the IDNR so sampling can be facilitated. Reports of potential wildlife disease events can be made by contacting Dr. Chris Jacques, IDNR Wildlife Disease, Large Carnivore, and Invasive Species Program Manager, at (773)636-0819. Typically, only mortality events involving five or more wild birds are investigated.

To learn more about HPAI in North America and the recent updates and detections, visit the link at USDA APHIS.

Mitch Oswald is a Wildlife Disease Biologist for the United States Department of Agriculture’s branch of Wildlife Services. Oswald is a 2014 graduate of Blackburn College in Environmental Biology. He currently works in the State Office in Springfield and has overseen disease surveillance projects for the agency since 2019. He is an avid outdoorsman and enjoys hunting, fishing and anything that gets him outdoors. He currently resides in Carlinville.

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