The Yosemite National Park email alerts warned of hantavirus pulmonary syndrome, which can be carried in the urine, saliva and feces of infected deer mice.
Health officials learned this weekend of the second hantavirus death, which killed a person who visited the park in June, spokesman Scott Gediman said in a statement. The first death was reported earlier this month.
Two other infected people were expected to survive.
The disease can incubate for up to six weeks before flu-like symptoms develop. It's fatal in 30 per cent of all cases, and there is no specific treatment.
All of the at-risk visitors had stayed in the "Signature Tent Cabins" in the park's Curry Village. Yosemite officials warned those who stayed in the village's 408 canvas-sided and wood-sided cabins from mid-June through the end of August to beware of any symptoms of hantavirus, which can include fever, aches, dizziness and chills.
"This is a serious public health issue and we want to be transparent, but at the same time we don't want people to alter their plans because we are taking the necessary precautions," said park spokesman Scott Gediman.
A 37-year-old man from the San Francisco Bay area was one of the victims who died. Details about the others have not been released because of medical privacy laws.
Gediman said contractors are working on the cabins, which cost about $140 for a night's stay, to protect park-goers.
"There are rodents and some are infected and that's what happens," Gediman said. "This is a wilderness setting. It has nothing to do with the cleanliness of the cabins."
This year's deaths mark the first such deaths among park visitors, although two others were stricken in a more remote area in 2000 and 2010, officials said.
Of the 587 documented U.S. cases since the virus was identified in 1993, about one-third proved fatal.