Officials said the Californians contracted hantavirus cardiopulmonary syndrome, a rare but often fatal lung disease, possibly by being exposed to contaminated mice droppings or urine while vacationing at the park, CNN reported.
A 37-year-old man from the San Francisco Bay area died in July, said Dr. Vicki Kramer, head of the department's vector-borne disease section. A Southern California woman in her 40s is recovering, Kramer told CNN.
The two stayed in separate locations at a Yosemite camping village of about 400 canvas tent and wooden cabins, park officials said.
Officials have focused on deer mice, common in the eastern Sierra Nevada region.
"Rodents can infest a whole range of these structures," Kramer told CNN. "Deer mice can get in a hole one-quarter inch in diameter."
Rodent control is the primary strategy for preventing hantavirus syndrome, the Centers for Disease Control and Prevention in Atlanta said.
California's health department has worked with Yosemite National Park for years to reduce risks to visitors, Kramer said.
The agency and park public health officers said they routinely conduct rodent surveillance and inspections of park buildings and facilities.