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The search for the culprit behind songbird deaths

Swollen, crusty eyes. Disoriented behavior. Stumbling and twitching. Sick and dying birds in the Washington, D.C., area were seen exhibiting these strange symptoms in the spring. That’s when University of Pennsylvania School of Veterinary Medicine professor and toxicologist Lisa Murphy started hearing reports and receiving deceased birds and tissue samples for testing. By early June, similar reports began coming in from Pennsylvania.

“And it kind of blew up from there,” says Murphy, who directs the Pennsylvania Animal Diagnostics Laboratory System (PADLS) facility at Penn Vet’s New Bolton Center, and co-directs the Wildlife Futures Program, a partnership between the School and the Pennsylvania Game Commission.

The condition has been linked to bird illnesses and deaths in at least eight other states, affecting a dozen songbird species—including many common backyard visitors, like blue jays and starlings.

Upon guidance from experts, bird lovers across the eastern U.S. have been taking down bird feeders, cleaning bird baths, and spreading the word about the emerging issue. And while experts have yet to pin down a definitive cause, Murphy and Penn Vet colleagues, working with partners in the Game Commission, the U.S. Geological Survey’s National Wildlife Health Center, and the other PADLS labs in the state, have been leading the effort to match the mysterious disease with a diagnosis. 

“It’s detective work,” Murphy says. “We enjoy the challenge.”

For the last two months, the PADLS lab team at New Bolton Center have been analyzing birds suspected to have succumbed to the disease. Currently, affected birds are mostly young fledglings of a dozen common songbird species. Many cases involve an impact to the birds’ eyes—a discharge or crusty and swollen appearance—or apparent neurological symptoms, such as disorientation, stumbling, and head twitching. And while cases were first spotted in the mid-Atlantic, they’re now seen in the Midwest and states farther south.

But finding the “why” has proved challenging.

“Ideally, you’d have the perfect case history,” Murphy says. “Even with domestic animals, we usually don’t have that, and with wildlife it’s even more rare. Typically it’s just, ‘It was found dead.’” 

Further complicating matters, the animals the lab receives have often been dead for long enough that decomposition may cloud the cause of death. Microbes could flourish, even if those were not the culprit behind a sickness.

What does help is numbers, so diagnosticians can look for patterns across samples. Erica Miller, a wildlife veterinarian and field operations manager for Wildlife Futures, is evaluating reports from community members, which now number over 1,500. Penn Vet wildlife health technicians are also working with the Pennsylvania Game Commission in each of six regions of the state. 

Meanwhile, diagnosticians in the PADLS lab have been running tests to identify the cause. So far, they’ve ruled out several possibilities, which may not bring the satisfaction of a positive identification but is crucial nonetheless.

“A disease like avian influenza is important on a number of levels, from bird health to human health to agriculture, and so as we rule out some of these high-consequence diseases early on, that’s a helpful thing,” Murphy says.

The researchers have not found evidence that the condition is a result of avian influenza, and have also ruled out West Nile virus and other flaviviruses, Newcastle disease virus, and other paramyxoviruses, herpesviruses, and poxviruses; and Trichomonas parasites. They don’t believe it’s related to a similar-looking conjunctivitis that has affected house finches this year. 

Other sensitive and specific tests look for toxins that could contribute to the current outbreak, such as pesticides or other manmade chemicals in the environment. Yet, just as with microbes, birds can harbor a certain level of chemicals in their bodies, without grave effects. The goal is to screen out these “background” toxins and microbes from the true cause of this outbreak.

For now, Pennsylvania and many other states have issued guidance to residents to take down bird feeders, clean feeders and bird baths with a 10% bleach solution, and avoid coming into contact with a dead bird or letting a pet do so. 

“If this is a transmissible disease, that’s one way we can discourage birds from having close contact with each other and even with different wildlife species,” Murphy says.

Within PADLS, reseachers are continuing to pursue and refine their diagnostics testing, hoping their persistence pays off. “This is why we do what we do,” says Murphy. “Not only do we want to know the diagnosis, but the value of knowing is it gives us the ability to intervene.”

Lisa Murphy is an associate professor of toxicology in the Department of Pathobiology at the University of Pennsylvania School of Veterinary Medicine.