A New Virus is Attacking North America’s Wild Turkey Populations
Hunters chasing down their Thanksgiving gobblers may not be able to detect virus from sight alone
As Thanksgiving nears and gravy-drenched pieces of hot turkey induce culinary daydreams, wildlife biologists are trying to connect the dots on a virus that has started to infect North America’s wild turkey population.
Photo by Don Greene
Lymphoproliferative Disease Virus, known as LPDV, has been present in domestic turkeys in Europe and Israel for decades, but in the last few years, biologists have started confirming cases in wild turkeys in the eastern United States. Some of the infected birds have lesions on their head and feet, although many of the sick fowl are not symptomatic, making their identification difficult.
Wild turkeys draw their ecological importance from being an integral part of the food chain. Gobblers, according to the Vermont Fish & Wildlife Department, provide sustenance to predators like coyotes, foxes, hawks, owls, and people, among other mammals. A landscape without wild turkeys is one that would affect the hunting community and small predators.
At this point, there seems to be as many unknowns about LPDV’s spread in the United States as there is confirmed information, but the researchers are working on answers.
Dr. Justin Brown, assistant research scientist and diagnostician with the University of Georgia’s Southeastern Cooperative Wildlife Disease Study, said his team confirmed its first diagnosis of LPDV in 2009 by a process of elimination. He said the larger wildlife diagnostic laboratories received infected specimens and tested the turkeys for known diseases that cause lymphoid tumors. Brown’s team took the testing one step further, and the discovery was surprising.
“[W]e had a virologist who worked up the case a little bit more and screened it for all of the oncogenic, or cancer-inducing, viruses that are in North America,” Brown said. “And when he came up negative on all those, he screened it for LPDV. … And it came up positive — all tissues.”
Over the next three years after that initial discovery, the team screened more turkey specimens, and 40 cases came back positive for the virus. “[I]nfection can occur even in the absence of tumor formation,” Brown said. “And so from there what we decided to do is sort of expand on this and do a larger survey of turkeys that had no clinical signs of disease, and so for this we used hunter-killed birds. And we went out and screened 1,100 birds that were hunter-killed birds from throughout the eastern US.”
Efforts are currently underway to screen these birds and figure out the prevalence of the virus. Early indications are that LPDV is common in this test group of turkeys, but many unknowns remain. For example, Brown said pinpointing where these infected turkeys reside is difficult. The best he could estimate was “throughout the eastern US.”
Hunters and hikers who come across wild turkeys may not be able to determine whether a bird has LPDV from sight alone. The lesions that several people have seen on the turkey’s head and feet are also found in birds with avian pox, a more common disease. A few LPDV specimens that Brown has researched have had lesions — essentially tan, round nodules — on the internal organs.
“Ideally when you’re looking at virus, what you would do is culture them, to put them in virus isolation and actually then you know you have an intact virus that can replicate that is ready to go,” he said. “And unfortunately at this point no one knows how to culture this virus, so we don’t know how to do that virus isolation.”
Another variable is whether the virus is causing fatality among infected birds. Brown said the majority of tested turkeys may have died of other causes, such as bacterial infections or trauma. There’s an unconfirmed theory that the virus may spread horizontally, through contact. Whether the virus spreads vertically, through the egg, has not been determined.
Right now, Brown’s team is small but collaborative. “Certainly more and more people are getting interested in this,” he said, adding that his team works with state wildlife agencies, Cornell University researchers, officials with the New York Department of Environmental Conservation and virologists with the USDA’s Avian Disease and Oncology Laboratory in Michigan.
Michael Schiavone, wildlife biologist and small game coordinator with the NYDEC, monitors the turkey population in the Empire State. In the 1990s, wild turkeys in New York rebounded to unprecedented levels thanks to restoration efforts and a rabies outbreak that reduced the number of raccoons, a common predator of the symbolic fowl. The population peaked in 2001.
“[T]here’s kind of been a gradual decline since then,” Schiavone said. “And part of that I think is a natural contraction coming down from those really high populations after restoration occurred. And then there are some other factors going into it, things like habitat, things like predation.”
Overall numbers are still enormously high when compared to populations in the early part of the twentieth century. The NYDEC reports that in 1930 North America had 30,000 wild turkeys; today that number hovers around 6.4 million. But the number of toms/gobblers (adult male birds) and hens (adult female birds) has declined, at least in New York. “Turkeys I think [are] still viewed as abundant,” Schiavone said. “And you still feel like when you’re out there, that they’re an animal that you can readily see and enjoy on the landscape, but they’re definitely not at the peak levels that they were around 2001.”
As the NYDEC addresses the turkey declines, Schiavone is also keeping track of LPDV news. “What happened was we were getting reports about avian pox, which is not uncommon,” he said. “ [W]e started looking for [LPDV] and not just New York, but states throughout the Northeast are looking for this thing that we thought was avian pox, and birds started testing positive. So what we’ve discovered is as we’ve tested birds, it seems to be relatively widespread.”
Schiavone said seemingly healthy birds killed by hunters are turning up positive for LPDV. “So we don’t know what it means right now, but we’re doing a lot of sampling and testing to figure what the distribution of LPDV is in New York and the Northeast,” he said. “It seems that where we look for it, we find it.”
A few years ago, Schiavone’s team would have told hunters that a turkey with lesions probably had avian pox. That’s not the case anymore. “But if you got a bird right now with lesions you wouldn’t be able to tell,” Schiavone said. “Because sometimes they can have avian pox, and sometimes they can have LPDV, and sometimes the two viruses can co-occur. And so if you saw a bird with lesions on it, you wouldn’t know one way or the other without doing testing.”
Over in New Hampshire, Ted Walski is dealing with similar questions involving the state’s turkey population. The turkey project biologist with New Hampshire Fish and Game said his department collected about 90 turkey feet during the spring hunting season for LPDV testing. The feet were sent to the University of Georgia team.
“The reason the feet were collected, it’s easier than collecting the liver or lungs or something because it’s messy — you know, blood and so forth,” Walski said. “And some lose some weight too because besides [the tumors] getting around one or two of the eyes, where they can’t see good and the predators grab them easier, they’ll get into the throat, too, and so they can’t feed as well and they start losing weight.”
Walski reported that his state has a healthy turkey population as high as 40,000 birds, which is more than he expected because of the winter conditions and loss of farmland. But in 2012, he sent half a dozen turkeys to a pathology lab at the University of New Hampshire, and the results showed that the wild turkeys had both avian pox and LPDV.
“Prior, it had been like you know one turkey out of this flock, one out of this group of four, but gotten in the last couple of months some where the whole brood of turkeys, several hens and the young each had those lesions on the head and neck,” he said. “We don’t have good, solid answers as to how long this is going to last, what percent of the population in a region or the whole state it might affect … Every animal, wild animal has its parasites and diseases, and some years you have to grin and bear it.”
With researchers working to isolate the virus and turkeys continuing to test positive for LPDV, Brown at the University of Georgia can report a solid, and somewhat startling, assertion.
“As far as what we’ve been finding in wild turkeys, this is the first detection in a non-domestic turkey host and the first detection in any host in North America,” he said. “I lean towards it being not a significant mortality factor on a population level, but I just don’t know at this point. It’s something that we can wait and see and hopefully get more information on in the future.”