Second Hantavirus-Related Death Confirmed in Mono County

MONO COUNTY, Calif. (MARCH 26, 2025) – Mono County Public Health has confirmed a second death
related to Hantavirus in the Town of Mammoth Lakes. Hantavirus is a serious and often fatal illness
spread primarily through contact with infected deer mouse droppings, urine, or saliva. Deer mice
are widespread in the Eastern Sierra region.
“Hantavirus Pulmonary Syndrome is uncommon but extremely dangerous,” said Dr. Tom Boo, Mono County
Health Officer. “We urge residents and visitors to pay attention to the presence of mice indoors
and other enclosed spaces and take precautions to reduce the risk of infection, especially when
cleaning up areas where rodent activity is present.”

Ongoing Investigation
Each Hantavirus case is investigated by local and state public health officials. The exposure for
one of the two confirmed cases this year may have occurred while vacuuming rodent waste, while the
other individual was likely exposed at home during a known infestation. A third possible case is
currently under investigation. Prior to these cases, the last confirmed Hantavirus infections in
Mono County occurred in 2019.

Since the first local case in 1993, Mono County has recorded 26 confirmed Hantavirus cases tied to
exposures in the county—the most in the State of California. Twenty of these infections were in
county residents, and six in people who visited Mono County and became infected. Two cases within a
three-week span during late winter are unusual, as most cases are typically reported in spring and
summer.
Rodent trapping in places where the first case may have been exposed found that 27% of captured
deer mice tested positive for Hantavirus—consistent with the county’s typical baseline of around
25%.

Health Risks and Symptoms
Hantavirus causes a severe illness that progresses rapidly once the lungs are involved. Early
symptoms usually include fever, fatigue, headache and muscle aches, sometimes with gastrointestinal
symptoms, followed by coughing and shortness of breath. The disease is often fatal, with a
mortality rate of approximately 30%. Prompt diagnosis and treatment improve outcomes, but testing
is only available in specialized laboratories, making early recognition challenging.

Prevention is Key
Public Health urges community members and visitors to remain vigilant for signs of rodent activity,
particularly in homes, cabins, sheds, garages, and other enclosed spaces. Infested vehicles may be
risky too. Follow these guidelines to reduce your risk:

• Seal up all gaps in your home larger than a pencil’s width to prevent mice from
entering.
• Store food in rodent-proof containers.
• Trap mice using snap traps (not glue or live traps).
• Avoid vacuuming or sweeping rodent droppings, nests, or urine.
• Air out enclosed spaces for at least 30 minutes before activities.
• Spray contaminated areas with a disinfectant or a freshly made 10% bleach solution and let sit
for five minutes before wiping clean.
• Wear gloves and an N-95 (or higher) mask when cleaning. Contact Public Health for free N-95
masks.

Do not eat food that may have been contaminated by rodents, and always wash your hands thoroughly
after any potential exposure.

Mono County Public Health can be reached at (760) 924-1830. The California Department of Public
Health has more hantavirus information at:
cdph.ca.gov/Programs/CID/DCDC/Pages/HantavirusPulmonarySyndrome.aspx.