The two campers were both diagnosed with the hantavirus pulmonary syndrome (HPS), which is a virus passed by exposure to mice droppings or urine. Officials believe they two people may been exposed to the virus while vacationing in Yosemite in June. The two people were not together, but were camping near each other at the same period of time. Both people came down with the HPS virus in July.
"This disease can frequently become fatal, but there are steps you can take to reduce your exposure," said Dr. Ron Chapman, director of the California Department of Public Health.
CDPH and Yosemite officials say they routinely conduct rodent surveillance to monitor deer mouse abundance and virus activity in mouse populations. Yosemite also conducts routine rodent inspections of buildings throughout the park.
Not all deer mice carry hantavirus, but deer mice with hantavirus have been found throughout the United States.
Since HPS was first identified in 1993, there have been 60 cases in California and 587 cases nationally. About one third of HPS cases identified in California were fatal. The two recent cases bring the total California case count for 2012 to four. Case-patients have been exposed to hantavirus in many areas in California where deer mice live, particularly from the eastern Sierra Nevada region and at higher elevations.