Three cases of Hantavirus Pulmonary Syndrome have been confirmed, and a fourth is suspected, Southern California Public Radio reported.
The National Park Service put out an alert to doctors and hospitals across the country.
The California Department of Public Health said a man died in the San Francisco area in July and the other death occurred last weekend in Pennsylvania. Both had stayed in Curry Village, a popular place for visitors in Yosemite that offers cabins and tent cabins, as did others confirmed or suspected of having the disease.
"To see a cluster of what right now is three, possibly four cases that are all associated with one location -- not one family but different people in the area -- that's unusual," said Dr. David Wong, head of the National Park Service Department of Public Health epidemiology branch.
The virus is carried by deer mice, a species mostly found at high elevations. People are typically infected from breathing the dried feces of infected mice.
The disease was identified 20 years ago.
Theater accidentally screens 'Nymphomaniac' trailer instead of Disney's 'Frozen'
Kate Moss Playboy shoot is classic Playboy, classic Kate