On March 28th and 29th, 2016, District staff, in conjunction with the California Department of Public Health, trapped and tested rodents for Sin Nombre hantavirus at San Bruno Mountain State & County Park. Each rodent was anesthetized, then measured and checked for parasites. Laboratory staff then drew blood for the hantavirus antibody test. After recovering from anesthesia, each rodent was carefully released at the exact location where it was trapped. Staff tested a total of 15 mice.

Preliminary test results showed that a few of the animals tested had antibodies to Sin Nombre hantavirus, but the number of animals trapped was too small to draw any conclusion on the prevalence of infection. Surveillance from 1975 to present day has shown a 7.5% infection rate of Peromyscus mice at trapping sites along the coast and at San Bruno Mountain in San Mateo County.

Although no human cases of HPS have been determined to be contracted within the county, an abundance of caution is recommended when handling live or dead mice or cleaning up after rodent infestations. More information about hantavirus and recommendations for safe clean-up can be found here.

Sin Nombre hantavirus is the strain of hantavirus that causes Hantavirus Pulmonary Syndrome (HPS) in California. It is typically contracted through exposure to the dried urine of Peromyscus maniculatus (deer mice) in enclosed spaces. One to five weeks after exposure, an individual may experience flu-like symptoms, followed by nausea and vomiting, then difficulty breathing. Counties in California where exposure to Sin Nombre Virus is highest are Mono, Inyo, Mariposa, Tuolumne, Nevada and Kern Counties.