San Mateo County: Surveying for Tularemia on the Coast

Entomology Report Frebruary 2008, San Mateo County Mosquito Abatement District

On February 27, the district trapped rodents south of Pescadero to test for tularemia. Tularemia is a bacterial disease of wildlife (primarily rodents and rabbits) that can sometimes be transmitted to people. Symptoms include abrupt onset of fever, chills, muscle aches and progressive weakness. When a person is infected by a tick bite, there is often a skin ulcer at the site of the bite and the local lymph nodes are swollen. The disease can be acquired from ticks or exposure to the tissues of infected animals, such as rabbits. Tularemia is not passed from one person to another and is treatable with antibiotics.

There have been two cases of tularemia in children in San Mateo County in the past 3 years. Both cases appear to have been caused by exposure to infected ticks at a location south of Pescadero along the coast highway. Tularemia has been detected in ticks collected at this site. In 2007, the bacteria was detected in 3 out of 102 adult American dog ticks (Dermacentor variabilis) and in 5 pools out of 128 adult Pacific coast ticks (D. occidentalis). The prevalence of infection in these ticks was 3 and 4%, respectively.

The survey conducted this month was aimed at assessing the level of infection in reservoir hosts. A total of 150 live traps were set and 12 animals were collected. Collections included 5 deer mice (Peromyscus maniculatus), 4 harvest mice (Reithrodonomys megalotis) and 3 California meadow voles (Microtus californicus). Blood samples obtained from these animals will be tested for serological evidence of exposure to tularemia by scientists at the Centers for Disease Control (CDC). Ultimately, the district plans to conduct monthly trapping and collect samples from at least 50 mice.

This project is a collaboration between the district, the San Mateo County Health Department, the California State Department of Public Health, and the CDC.