FILE: Deer mice in a nesting box.
Michael Siluk/Getty Images
It’s been nearly a year since three people died in Mammoth Lakes due to hantavirus, and the popular ski region is still taking precautions seriously.
Justin Caporusso, the Mono County public information officer, told SFGATE in a phone call last month that last year’s fatal exposures to hantavirus — which is spread in the Eastern Sierra through the droppings or saliva of infected deer mice — were “a complete seasonal anomaly.”
Article continues below this ad
“It mostly occurs in warmer months, so we often launch campaigns towards later spring,” he said. “So when it was still winter, that kind of threw us off as well.”
Three people died in the first few months of 2025 of hantavirus pulmonary syndrome, a rare disease caused by hantavirus infection, including one 26-year-old Mammoth Mountain Ski Area employee, as SFGATE previously reported. While there was never a definitive link found between the individuals, health officials found deer mice droppings in each of their workplaces.
At the time of the deaths last year, Dr. Tom Boo, Mono County public health officer, explained that there was likely an increase in deer mice populations that year throughout the Eastern Sierra, which resulted in an increase in droppings. Mono County has had only 27 recorded cases of hantavirus since 1993.
Color-enhanced transmission electron micrograph of hantavirus particles. Hantavirus is a respiratory disease carried in wild rodents such as deer mice.
Science Photo Libra/Getty Images
“It was an unprecedented year and really quite scary even when it’s a virus you’re potentially familiar with or used to hearing about,” Caporusso told SFGATE, continuing: “To escalate to this level with local deaths, it was quite a big deal. I think that allowed for the opportunity for the county to step into action.”
Article continues below this ad
Make SFGATE a preferred source so your search results prioritize writing by actual people, not AI.
Add Preferred Source
In a release last April announcing Mono County’s third death from hantavirus, the county health department said, “We believe that deer mouse numbers are high this year in Mammoth.” Officials encouraged people to close any holes larger than a pencil’s width and to store food in mouse-proof containers. If people did encounter droppings in their homes, the department warned them to wear masks and gloves while cleaning up the droppings and specifically to not vacuum them, because doing so could aerosolize the droppings and spread the particles through the air.
Rodrigo Becerra, the 26-year-old man who was fatally infected with hantavirus last year, was an avid skier and worked for Mammoth Mountain Ski Area. He lived in employee housing. Health officials found mice droppings in his workplace but said there was no evidence of rodents in his home.
Emily van Greuning, a communications manager for the resort, told SFGATE in a March email that Mammoth Mountain has a comprehensive hantavirus policy that was put in place well before last year’s deaths.
Article continues below this ad
Mammoth Mountain, pictured here in 2024, is in the rugged Eastern Sierra.
Lester Black/SFGATE
“The policy was not implemented in response to those events and remains part of the company’s longstanding health and safety protocols,” she wrote. “As an added precaution, Mammoth Mountain engaged an independent third party to deep clean select spaces. This step was taken out of an abundance of caution and was not prompted by any identified contamination.”
She also said that regular inspections are conducted across all Mammoth properties and that employees receive required training on how the virus is contracted, what symptoms are associated with the virus, activities that can increase the risk of contracting it, and preventive measures.
The Mono County health department has been doing ongoing outreach to educate the public on hantavirus each year, Caporusso said, but “last year, we took swift comprehensive action to step up and educate the community after the deaths.”
Article continues below this ad
Mono County has partnered with Inyo County and the California Department of Public Health on its public outreach campaigns. It has also worked closely with Mammoth and Northern Inyo hospitals and national health experts to “help spread the word” about hantavirus, Caporusso said. Mono County has also reached out to the Indian Health Service hospital in Arizona and the University of New Mexico for guidance on precautionary measures, as both states have “extensive experience” with the risks of dealing with exposure to hantavirus, Caporusso said.
Two people who died from hantavirus last year visited Mammoth Hospital, pictured here in April 2025, and were discharged before their deaths.
Lester Black/SFGATE
Considering the large Spanish-speaking population in Mammoth, the county launched a major bilingual public health campaign, which Caporusso said has reached radio and print. The department also “went door to door to businesses” in Mammoth Lakes and offered N95 masks.
“We really hit it from as many angles as we could,” he said. “We’re a strong, tight-knit community who all watch out for each other but are isolated and we’re frontier, so it makes things all the more scary.”
Article continues below this ad
SFGATE reached out to Mammoth Hospital in Mammoth Lakes, where Becerra had sought treatment before he died, as well as Northern Inyo Hospital in nearby Bishop, for information about any updates the hospitals have made to hantavirus treatment protocols since last year. Neither got back to SFGATE in time for publication.
However, Caporusso told SFGATE that as of the end of March, no other hantavirus exposure had been reported in the county in the past year.