A public health crisis has begun to spread out of Yosemite National Park, where four visitors were infected with the little-known Hantavirus earlier this month.
The infection left two of them dead and has left the National Park Service nervous — so nervous they've sent letters to 1,700 park-goers who were potentially exposed.
"There have been fewer than 600 cases in 19 years," explains McKenna. Hantavirus is thought to be contracted not from direct contact from rodents (including mice bites) but from indirect contact with their droppings and urine.
Because of that it's "tough to know if you're infected."
"It's a mysterious and kind of sad outbreak," McKenna says. "The minimum time between when you're exposed and when you develop symptoms is a week but maximum is a month. So you can be long gone from vacation."
Adding to the complications with ID'ing the disease is the fact that all the symptoms "feel like the flu." The most distinctive among them, according to McKenna, is difficulty breathing, characterized by a feeling like a "tight band around [your] chest."
The first known U.S. outbreak of Hantavirus occurred in 1993, when 48 were known to be infected and about a third of those died.
"People tend to think illnesses go after the oldest, youngest, most compromised," explained McKenna. "But first big outbreak was notable because it was the young, healthy people who were dying."
Other cases were thought to be rampant before 1993, but are undocumented -- at least in English. McKenna says that at least one other major outbreak was thought to occur in the Korean War, but while there was information on the illness in Japanese and Chinese medical literature no one at the time had translated it.
The CDC has provided an information sheet on how to avoid the virus (and what to do if you think you're exposed) but, as McKenna says, "If we didn't do the things that're potentially risky in our lives, we'd never leave our houses."