San Mateo County Mosquito and Vector Control District continues to find evidence of hantavirus infection in deer mice collected during routine rodent-borne disease surveillance. The most recent samples were collected during May and June of 2016 in the vicinity San Bruno Mountain and Montara.

Deer mouse Image/CDC
Deer mouse

Hantavirus is a viral disease carried by wild rodents – in California, by deer mice in the genus Peromyscus – and is most frequently transmitted when humans breathe in dust contaminated with the urine, saliva, or droppings of infected rodents, such as when opening or cleaning previously unused buildings. Commensal rodents, such as house mice, roof rats, or Norway rats, do not carry hantavirus.

Symptoms of hantavirus infection usually develop between one and 8 weeks following exposure. Early symptoms include fatigue, fever, and muscle aches, followed by a severe respiratory infection that is often fatal. There is no treatment, cure, or vaccine for hantavirus infection.

District manager Dr. Chindi Peavey says that these results are not surprising: since 1998, hantavirus has been detected routinely throughout San Mateo County, including at San Bruno Mountain, the Crystal Springs Watershed, and Wunderlich Park. “There has never been a human case of hantavirus acquired in San Mateo County,” Dr. Peavey said, “but we do know that hantavirus circulates at low levels in deer mouse populations in our county.”

Residents of and visitors to rural areas of San Mateo County are reminded to take precautions to reduce their risk of hantavirus exposure, including:

  • Rodent-proof homes and other structures to keep mice out; clear vegetation and debris around homes that may provide habitat for rodents
  • Take precautions when cleaning up after rodent infestations or entering structures that have not been entered recently; never sweep, vacuum, or breathe in dust in areas that may have been contaminated by rodents
  • Avoid contact with rodents and their nests when hiking and camping, including when using cabins and trail shelters