Rodent-Borne Disease Updates

Laboratory staff conducted two surveys of wild rodents in the month of June. The surveys took place in Water Dog Lake park in Belmont on June 14th and 15th and Eaton and Big Canyon parks in San Carlos on June 20th and 21st.  Blood samples were taken from captured rodents by a subocular bleed with a microcapillary tube and ear punches were also taken from the rodents. The blood and ear tissue will be tested in our District laboratory for Borrelia bacteria that cause Lyme disease and other infection. Addtionally, blood samples from Water Dog Lake were sent to the California Department of Public Health (CDPH) for testing of hantavirus. Results of the hantavirus testing revealed a very low level of hantavirus in one of six Peromyscus mice at Water Dog Lake. The most likely explanation for the low level positive is that the mouse was carrying a strain of hantavirus that is not Sin Nombre virus. Sin Nombre virus is the only type of hantavirus that is known to cause human infection in the western United States. Other strains of hantavirus can be present in rodent hosts.

In May the District performed a rodent survey in the same area and detected hantavirus in four of ten Peromyscus mice. District staff will be following up with another rodent survey in the same area in July to acquire a larger sample size of mice for testing. A larger sample size will provide a better approximation of the percentage of Peromyscus that are carrying hantavirus. The mice carcasses will also be sent to (CDPH) to be used in a study to determine which strains of hantavirus are present in different geographic regions of California.