Key Points Researchers have discovered a variant of the rustrela virus (RusV) in a wild mountain lion in Colorado. This is the first documented case of the rustrela virus linked to "staggering disease" in North America. Staggering disease, a severe neurologic condition, has primarily affected domestic cats in Europe, particularly in Sweden and Austria. The affected mountain lion, a young female, was euthanized after showing symptoms of hind-limb ataxia. The rustrela virus, related to the rubella virus, was identified through collaboration with…