Fourteen adult elk around Blekinge in southern Sweden have recently been found in the woods in severe states of paralysis, emaciation and blindness, TT/TheLocal.se reported Friday.
The blindness has resulted in some elk being killed in traffic accidents, but experts say they have no clue as to what is causing the symptoms.
"There is no scientific explanation," Lennart Balk of Stockholm University told the Aftonbladet newspaper.
Balk pointed to the tens of thousands of wild birds that have also died in the area from a lack of thiamine, or vitamin B1, as a possible link.
"We see that the elk are infected with the same clinical symptomatically, but it is too early to say whether it's the same disease," he said.
Viral and parasitic infections and possible contaminants in the environment have been ruled out, scientists said.
"It's a mystery. These are animals that are in good condition," Torsten Morner of the National Veterinary Institute said.
"They are confused, and the one bull we had in was emaciated. We don't know what's causing it."
It's "strange" that something would stop an elk from eating over the summer, he said.