The bald eagle holds a special place in the heart of many Americans. Not only is it the national bird of the United States, but it also holds great honor and respect within Native American culture. Once an endangered species in the United States, the bald eagle has now since bounced back in ever-increasing numbers.
However, a new threat is possibly endangering the bald eagle population: an unknown type of virus that hasn't been observed before.
In 1994, bald eagle populations in Wisconsin started exhibiting several deficits related to the nervous system, such as poor coordination, seizures, vomiting, and more. Scientists termed this as Wisconsin River Eagle Syndrome (WRES), which often leads to death shortly after.
Researchers from the University of Wisconsin-Madison, the Wisconsin Department of Natural Resources, and the U.S. Geological Survey National Wildlife Health Center examined bald eagle tissues to investigate possible causes of WRES. They came across a previously unidentified virus that could hold the answer they're looking for, which they called Bald Eagle Hepacivirus (BeHV). They published their findings in the latest issue of Nature's Scientific Reports.
The researchers found that a common WRES characteristic was a specific type of damage to liver tissue, which was often caused by viral infections. With this, the researchers hypothesized that a virus was most likely the cause of WRES, which they found in nine of their specimens. They found that the genetic makeup of this unknown virus was similar to duck hepacivirus as well as the Hepatitis C virus in humans, hence its name.
Of the 47 different specimens of eagle tissues they collected from seven states, they found that almost a third of them were infected with BeHV.
Wisconsin populations are hit the hardest. Eagles from this state were much more prone to infection with BeHV, around nine times more likely than the average. The researchers estimate that the prevalence of BeHV in Wisconsin is at 75%, compared to the average of 23%.
The role that BeHV might have with regards to WRES is still uncertain, although it was found that the virus persists mostly in the liver. Malfunctioning livers lead to the buildup of toxins in bald eagles' bodies, manifesting in neurologic deficits like those observed in WRES. Interestingly, the damage caused to bald eagle livers was much like what's observed in human livers.
It seems like WRES and BeHV are inextricably linked, especially since all the eagles infected with WRES came from Wisconsin in particular. However, this doesn't seem to be the case as BeHV was also found in eagles that didn't display signs of WRES. It seems like there's more to the story, which the researchers are still trying to figure out.
Whether BeHV is the direct cause of WRES remains to be seen, and more work still needs to be done. One of the researchers, Sean Strom, shares his thoughts on the matter in a press release:
"We don't think this virus is having a serious impact on the bald eagle population, but the fact that WRES is an unknown condition keeps our interest. This study is another piece of the puzzle. Hopefully, we can find more pieces and figure out what is happening."
