LOS ANGELES (MCT) — A second hantavirus death has prompted partial closures of a popular Yosemite National Park campsite and warnings to 1,700 recent visitors as officials try to understand what is being characterized as an “unprecedented” outbreak of the disease.

After learning that a Pennsylvania visitor’s death was caused by hantavirus, Yosemite officials sent emails Monday evening to those who stayed in the “signature tent cabins” in Curry Village between mid-June and late August, said park spokesman Scott Gediman. Letters were sent to visitors whose email addresses were not on record.