Vickie Mates is with the National Park Service. She says the latest case involves a California resident who stayed in the "Signature" cabins in the park's Curry Village in early July.
"This particular case is a little different than the other eight," says Mates. "This person was infected with Hantavirus but did not fully develop the pulmonary syndrome, and this person has recovered."
Three of the nine park visitors who contracted the illness have died. The majority of the cases involved guests at the Curry Village cabins.
Mates says this week the park expanded its outreach efforts by sending notices to the roughly 230-thousand people who stayed overnight anywhere in Yosemite since the beginning of June.
The disease is carried in the feces, urine and saliva of deer mice and other rodents, and carried on airborne particles and dust.