Understanding disease prevalence in Pennsylvania wild turkeys

Known to affect domestic turkeys in the U.K., Austria, the Netherlands, and Israel since the 1970s, lymphoproliferative disease virus (LPDV) was not recognized in wild turkeys in North America until 2009, making this retrovirus that results in organ and skin tumors relatively new to researchers.

Erick Gagne, assistant professor of wildlife disease ecology at the University of Pennsylvania School of Veterinary Medicine, says the disease can cause cancer in some cases. But the prevalence in Pennsylvania wild turkeys, population-level impacts, and co-infection with other diseases—such as reticuloendotheliosis virus (REV)—remain unknown. He and other researchers from the Wildlife Futures Program at Penn Vet are working to answer these questions.

Gagne and Eman Anis, assistant professor of microbiology at Penn Vet, are leading the Wild Turkey Health Project, Penn’s contribution to a larger, multi-year turkey monitoring study in collaboration with Penn State and the Pennsylvania Game Commission. To analyze movement data and habitat use, Game Commission researchers are putting GPS trackers on turkeys, which provide location and movement information such as when a bird is nesting or has died.

“Is the movement through the landscape as well as habitat use different between turkeys with prevalence of LPDV and other viruses, as well as turkeys that are co-infected?” questions Mary Jo Casalena, wild turkey biologist for the Game Commission. She says this is the first large-scale disease project looking at population-level impacts of LPDV and other viruses on reproduction and survival.

Casalena says the project came about because of substantial variation across Pennsylvania over the past decade in whether turkey populations are increasing, stable, or declining—and the Game Commission wants to know why. 

“One of the objectives of the Wildlife Futures Program is to really have these integrated research projects, where you have folks at Penn Vet with expertise develop research projects that address the needs and concerns of the Pennsylvania Game Commission to manage and conserve wild birds and mammals in the state in general,” Gagne says.

Knowing about the attributes or habitats of turkeys in areas where turkey populations are increasing, Casalena says, can shed light on how habitat managers like herself can increase turkey populations where they are low. The issue may come from weather patterns, which the Game Commission can’t control. But if turkeys need higher quality nesting and brooding habitats, wildlife managers can help, and they could be able to help turkeys avoid disease.

“This study I see as the first step,” Casalena says. “You have to understand what’s going on and make those management recommendations, and then do those prescriptions—those changes to the landscape—and see if they have population-level effects.”

Since the problem is not unique to Pennsylvania, the Game Commission has invited other states to join the study, and Maryland, Ohio, and New Jersey have come on board. Casalena says their goal is to track at least 25 turkeys per site annually, and each state has between two and four sites.

From the field to the lab

The Game Commission is leading the field crews doing turkey trapping at four sites across the state, which includes affixing GPS monitors—which Casalena says have accelerometers that can tell researchers whether the birds are feeding, walking, flying, or stationary—and collecting blood samples for disease testing, before releasing the turkeys back to the wild..

The annual turkey trapping season lasts from late December through mid-to-late March, Casalena says, and the project is now in its third season, following trapping seasons in 2022 and 2023. There will be one more field season next year.

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Gagne says Penn researchers did initial disease testing after the past two trapping seasons and a lot of his team’s work is back-ended, that he will be hiring a postdoctoral fellow for two years and providing summer research opportunities to students.

Additionally, the Wildlife Futures Program has wildlife health technicians working across the state, and they have gone to a lot of the trappings. Casalena says the health techs provide quality control and have trained people from the Game Commission on blood sampling, and they are responsible for making sure the samples are handled and shipped back to Penn properly. 

Part of Anis’ job as section head of the Microbiology Lab at the Pennsylvania Animal Diagnostic Laboratory System is to get samples from different species to detect pathogens. Here, in addition to LPDV and REV, Anis says she is interested in mycoplasma, a type of bacteria that has been reported in domestic turkeys and can impact production and fertility. 

Anis says mycoplasma is difficult to isolate, but her lab uses polymerase chain reaction (PCR) testing to detect its nucleic acid. She says there isn’t much information on the prevalence of mycoplasma in wild turkeys but thinks it’s important to determine. “It would be very interesting to see how this pathogen can transfer in either direction, between domestic and wild,” Anis says. The final analysis of samples will take into consideration age and sex of each bird, she says.

Gagne and Casalena both cited a study from Maine—published in 2022—that found LPDV was becoming more prevalent in wild turkeys and was reducing clutch sizes by one egg on average. Casalena wants to know if hens positive for LPDV have lower clutch sizes, if that’s the case across states, and the cause of lower clutch size, such as a habitat issue or co-infection.

“Working with Penn and the Wildlife Futures Program opened the door for the Game Commission in terms of what we can learn for wildlife populations,” Casalena says. “We were limited in terms of what we could do disease wise, so now that we have all these experts in virology and pathology and all different types of wildlife disease, it just opens the door for so many different questions that we’ve had.”

This research is supported by the National Wild Turkey Foundation (NWTF) and the Pennsylvania chapter of NWTF.