Why Bird Flu Is Spreading to Mammals

Also known as “bird flu,” or just “avian influenza,” HPAI has been spreading rampantly across the country in waterfowl and domestic bird populations since last spring. And while it first took a large toll on wild turkeys and domestic pheasant farms in the Midwest, it now appears to be spreading to a host of other species. The USDA reports that the virus responsible for HPAI has also been detected in raccoons, skunks, red foxes, possums, and coyotes. The grizzly bears, however, appear to be the first cases of HPAI in large mammalian species in the United States.

“We suspect these mammals probably get the virus from consuming infected birds,” FWP Wildlife Veterinarian Jennifer Ramsey said in the press release. The virus is transmissible through the saliva, nasal mucus, and fecal matter of infected birds, meaning that scavengers and predators, like bears, are susceptible to exposure.

It’s unclear, however, if the virus can actually spread between mammalian species. More likely, individual animals are contracting it from a one-time exposure to dead, infected birds.

“Mammals are generally considered to be dead-ends for highly pathogenic avian influenza,” Dr. Megan Moriarty, a wildlife veterinarian specialist with the Michigan Department of Natural Resources said in an interview last fall. From a biological standpoint, the virus evolved in avian species, and cannot use mammals as a host for transmission. But it can still infect them. From reports of infected fox kits in Wisconsin to raccoons in Washington, small mammals across the country appear susceptible to the disease.

But the biggest effects are in wild duck and goose populations. States across the western US, particularly those intersecting major flyways, are reporting large waterfowl die-offs as a result of the disease. In Colorado, biologists have documented huge goose mortality events. “Total snow geese mortality numbers are unknown, but mortality reports range from a single animal to more than 1,000 dead geese on a single reservoir,” Colorado Parks and Wildlife (CPW) said in a press release. Wyoming Game and Fish issued a similar statement, saying hunters have reported seeing “large waterfowl die-offs” in the state.

Researchers believe migratory waterfowl populations are the primary reservoirs for the HPIA, making the outbreak difficult, if not impossible, to contain. Ducks and geese migrate hundreds to thousands of miles across North America, toting with them any diseases they might have. And, as is oftentimes the case with viral diseases, infected individuals may not appear symptomatic, but are still capable of spreading the virus. Thus, thousands of dead birds are just a superficial indicator of the level of proliferation this virus has achieved in waterfowl populations. In an interview with NPR, Richard Webby, an influenza specialist with the World Health Organization said, “The bird populations haven't seen viruses like this before, so in terms of their immune response, they're all immunologically naïve to this.”

The influenza is not restricted to wild bird populations, however. Commercial chicken flocks have taken a huge hit as well. Since early last year, over 58 million chickens have died from the disease itself, and millions more have been culled in an effort to stanch the spread. In March, nearly 5 million laying hens were culled at a single facility northwest of Des Moines, according to several Iowa newspapers. The outlook is grim for poultry that contract the illness: the virus compromises the function of multiple internal organs, leading to a 90 to 100% mortality rate, often within 48 hours.

While the death of commercial flocks isn’t readily visible to most people, consumers are seeing the effects, whether they know it or not. The cost of commercially available eggs has skyrocketed in the last few months as a result of limited supply. According to the Consumer Price Index, the cost of eggs has increased 60% in the last year, with a dozen now fetching more than $7 in some areas.

The virus hasn’t spared backyard chicken flocks either. As implied by the name of the virus, highly pathogenic avian influenza, this particular strain is extremely virulent, meaning easily transmissible. It doesn’t necessarily take direct contact with an infected bird to spread the disease, either. Research conducted during a similar, albeit smaller, outbreak of influenza over the winter of 2014-15 indicates that the virus can spread miles as airborne particles, especially following high-wind events near commercial chicken pens or slaughterhouses. As such, the magnitude of the outbreak is difficult to fully realize.

“We have not had this virus in our part of the world on this scale before,” Richard Webby, an infectious disease specialist, told the New York Times in January. “In the world of flu, this is a pretty major event,” he continued.

While the 2014-15 outbreak killed over 50 million birds, it petered out in wild populations over the summer. Researchers, however, suspect that this year’s variation of the virus might be here to stay. The virus has already persisted through one summer, and should it continue to spread this spring, as appears likely, the chances of the virus mutating and spreading amongst other species, beyond birds, becomes increasingly more likely. But even as is, the HPIA remains “the largest foreign animal disease outbreak in U.S. history,” according to a spokesman for the USDA.

Fortunately, for now anyways, the influenza appears incapable of infecting humans. The CDC reports that there have been nearly 5,000 known, direct exposures to the disease, but only one confirmed case in humans. Even so, they recommend taking precautions when handling birds, domestic or wild, in the coming months.

In terms of the effects on wild waterfowl populations, they remain to be seen. CPW reports that “snow goose and most other waterfowl populations are currently robust and most species can likely tolerate relatively high losses this winter without impacting population viability.” But should the outbreak continue, that could change. In the meantime, hunters can expect to encounter dead and dying waterfowl at their favorite marshes and ponds.