In the most recent case, a California resident was sickened, possibly in a tent cabin in Curry Village, park spokesman Scott Gediman said. Eight cases have been linked to the cabins, the Los Angeles Times reported Thursday.
The latest case is considered a "hantavirus infection," unlike the previous cases, and the infected person has recovered, California health officials said.
The virus is usually transmitted through human contact with enclosed areas that have been infested with mice. The U.S. Centers for Disease Control said about one-third of the 587 cases diagnosed from 1993-2011 were fatal.
Public health authorities said the multiple cases in Yosemite were unusual, since it was unusual for there to be more than one case per year in one location, the Times said.
Investigators have not determined what caused the outbreak in Yosemite but officials said Wednesday there has been an unusually large deer mouse population this year.