Rodent Diseases in San Diego: Hantavirus, Leptospirosis and Rat-Bite Fever

Hantavirus and deer mice

The county says deer mice are the main carriers of a hantavirus called Sin Nombre virus, and that it is not spread person to person. Deer mice are found mostly in rural areas, the desert and the mountains. Around San Diego that means the backcountry, East County and North County inland, and homes next to canyons and open space. The county's 2026 brochure says house mice do not carry hantavirus.

People usually get sick by breathing in particles from droppings or urine that get stirred into the air. The county says most human cases happen when people occupy cabins or clean small, closed buildings where infected wild mice have left droppings.

Symptoms may appear 1 to 8 weeks after exposure, according to the county, and include severe muscle aches, chills and fever, headache or dizziness, trouble breathing or coughing, and nausea, vomiting or stomach pain. The county says there is no specific treatment or vaccine, but medical care can help. Call a doctor right away if you have symptoms after rodent exposure.

What the county's testing shows

The Vector Control Program collects blood samples from wild mice every year. The county says about 3 percent of sampled mice test positive on average each year. Its hantavirus page lists 16 positive rodents in 2025, with yearly totals ranging from 3 in 2016 to 53 in 2011. For 2026 so far it lists 7 positives, including western harvest mice, a California vole and a deer mouse, in San Diego and Carlsbad. The county also says rodents that carry Andes virus have not been found in the county.

Leptospirosis

The county lists leptospirosis among the diseases rats spread, through contact with infected urine or with contaminated water or soil. The CDC also lists leptospirosis among diseases spread directly by rodents. Wear gloves when cleaning areas with rat urine, cover cuts, and wash hands well afterward. Keep pets away from areas where rats have been, since dogs can be exposed too.

Rat-bite fever

The CDC says rat-bite fever is caused by bacteria that live naturally in rodents such as rats and mice, and that infected rodents look healthy. People can get it from bites or scratches, contact with saliva or urine, handling contaminated materials, or eating or drinking contaminated food or water. It does not spread person to person.

The CDC says symptoms usually start 3 to 10 days after contact and can appear up to 21 days later. In North America they include fever, vomiting, headache and muscle pain, with joint pain or swelling in about half of people and a rash in about 3 in 4. Antibiotics can cure it if started soon after symptoms begin. If a rodent bites or scratches you, wash the wound and call a doctor.

Other risks

The county also lists:

• Plague, spread through infected fleas or bites
• Food poisoning from food contaminated with rodent urine or droppings
• Parasites, including tapeworms
• Rat mites, which can bite people

The county notes rats can also damage structures and start fires by gnawing on wires. Throw out any food that rodents may have touched, and have chewed wiring checked by an electrician.

How to clean up safely

For urine and droppings, the CDC says to:

• Air out the space for 30 minutes before cleaning
• Wear rubber or plastic gloves
• Spray with 1 part bleach to 9 parts water, or 1.5 cups of bleach in a gallon of water, and let it soak 5 minutes
• Wipe up with paper towels and throw them in a covered trash can
• Mop or sponge the area with disinfectant
• Wash hands after removing gloves
• Never sweep or vacuum droppings, urine or nests

For closed spaces where wild mice may have lived, such as sheds, cabins and garages near open space, the county's 2026 brochure adds: air out at least 2 hours, wear a face mask and eye protection, and soak for 15 minutes. See rodent droppings cleanup.

Keep rodents out

Disease risk drops when rodents stay outside. The county's advice: seal openings, remove food and debris, keep woodpiles off the ground and away from walls, and trim vegetation back from the roof. The hantavirus brochure adds sealing holes dime-sized or larger, using snap traps rather than glue or live traps, clearing pet food daily and cutting grass and weeds within 100 feet of buildings. See how to get rid of roof rats and mouse control.