Purdue Health Sciences researcher investigates bird flu vaccination efficacy, lead exposure in California condors

Aaron Specht, Purdue University School of Health Sciences assistant professor, holds his portable X-ray fluorescence technology, which was used to measure lead exposure in California condors for a recent study.(Tim Brouk)

Written by: Tim Brouk, tbrouk@purdue.edu

Avian influenza, also known as bird flu, is back in the headlines as the viral disease has infected more than 13,000 wild birds in the United States in the past year, according to the Centers for Disease Control and Prevention (CDC). The life-threatening disease is responsible for some dramatic mass mortality events in wild birds, including when the bird flu began affecting U.S. agriculture as 24 poultry farms found infected chickens between 2024-25.

Bird flu doesn’t just infect birds. More than 40 dairy farms have had sick cows in the past 18 months, and 64 human cases have been reported in mostly dairy and poultry farmworkers. Current bird flu strains have not been found to result in infection through person-to-person contact, and the overall risk is low to people not working closely with birds or cattle. Only one U.S. farmworker has died from bird flu since 2024, according to the CDC.

Still, the disease is a serious threat to U.S. agriculture. Aaron Specht, assistant professor in the Purdue University School of Health Sciences, has investigated bird flu cases in critically endangered California condors since 2023, soon after 21 condors died from an avian flu event. Specht administered a vaccine developed by “animal health company” Zoetis for vultures to prevent the spread of bird flu. Specht also used his trusty X-ray fluorescence (XRF) technology to scan birds for potential lead poisoning and see how such an exposure would interact with the vaccine. This work was published in June by the CDC’s Emerging Infectious Diseases journal.

A California condor is prepared for an avian flu vaccination.(Aaron Specht)

Specht and his team first tested the vaccine on 20 black vultures, a common bird in the western and southwestern United States. Eight other vultures were unvaccinated but monitored as a control group. Most of the vaccinated vultures (19) showed positive signs from being vaccinated, according to the birds’ bloodwork. The same vaccine was used on the condors.

Of 20 vaccinated California condors, 18 showed positive reactions to the vaccine. These positive reactions to the bird flu vaccine could help preserve the California condor population, which is believed to have less than 600 left in the world.

“A lot of the condors that are released in the wild are captive bred,” Specht said. “We’re hopeful that in the future, we can create the environment in which they can again start rebuilding their own population through wild breeding.”

Vaccination details

Specht and his team randomly assigned 28 vultures to one of three treatment groups. One vaccinated group of 10 vultures were administered a prime-boost (two-vaccine) regimen typically used for poultry, in which a half milliliter was given on day one and again three weeks later. Another group of 10 vultures received a one-vaccine regimen of one milliliter on day one. The vaccine was given between the shoulder blades because that location is near the standard vaccine site used for poultry (back of the neck). Experienced wildlife husbandry professionals monitored all birds daily for signs of lethargy, reduction of food intake and other potential indicators of an adverse vaccine reaction.

The condors were treated in similar fashion. The two-vaccine regimen was given to 10 birds and the one-vaccine regimen to 10 birds while five unvaccinated birds were used as controls. Specht and his team had to vaccinate birds in multiple locations because California condors are difficult to find in the wild. Ten birds were vaccinated at the Los Angeles Zoo and Botanical Gardens, six at the San Diego Zoo Wildlife Alliance and four at the Oregon Zoo. No adverse vaccine effects were found in any condor.

Lead exposure analysis

Along with the vaccinations, Specht held his portable XRF machine to the vultures’ legs for three minutes to see if the specimens had ingested lead. This was conducted to see if there was a correlation between lead exposure and the vaccine’s efficacy because lead exposure is known to weaken the immune system in humans. With vultures and condors being carrion eaters, the scavengers have been known to eat the lead buckshot or bullets from hunters who leave their kills or the leftover gut piles of deer and other large game.

“In humans, we’re very concerned when a child comes in with their level of blood lead at 3.5 micrograms per deciliter,” Specht explained. “But it’s pretty routine for the condors to come in with 65 micrograms per deciliter or more. The highest one we’ve seen is close to 1,000. The lethal dose in humans is a little bit more than 100. So, these condors have the ability to survive with much higher doses of lead exposure. But it’s also killing them at drastic rates. So, the idea being we wanted to know that the vaccine was going to work in these conditions where you have these very, very high levels of lead exposure in each of the individual birds themselves.”

Initial vulture scans were executed 66 days after they were removed from the wild and 53 days after the start of the vaccine trial. An XRF device measures elemental radiation signals to noninvasively infer the amount of lead that has accumulated in bone, a technique used for years in humans and recently adapted for use with birds. XRF is better than a blood test because it can detect lead exposure from years previous. Blood tests only reveal a “snapshot” of lead levels.

“Bone gives us a measure of cumulative dose,” Specht said. “Looking at cumulative dose is a very effective way to determine how much they’ve been exposed, how much detriment we anticipate in their bodies in terms of the other organ systems being affected — neurological health, cardiovascular health. All these other things are very well-documented in humans but not as well-documented for some of these subtle impacts in birds and other species.”

Since all the condors in the study were raised in captivity, no XRF was used on the endangered birds. However, since lead exposure can negatively impact the immune system, it was important to investigate. In the vultures, no such link between lead exposure reduced immunity and the bird flu vaccine was found.

What about our chickens?

While a major thrust of this study was to help an endangered species’ survival, Specht’s work can apply to the poultry we eat. A bird flu breakout could be devastating to a chicken farm. Numerous major outbreaks could raise prices at the grocery store. Could vaccinating chickens against bird flu be viable?

Previous studies have found 100% of chickens showed positive reactions to bird flu vaccines. However, a major hurdle could present itself if the U.S. Food and Drug Administration does not allow the sale of vaccinated chickens for their meat and eggs.

“I think if we want to keep our chicken flocks away from the avian flu, this is a potential option moving forward — to use this vaccine to protect them,” Specht said. “It doesn’t seem like it’s going to be impacting much beyond giving them the capacity to resist the potential of the spread of this disease. I think it would be a great avenue to pursue, to keep our chicken flocks healthy and keep us healthy.”