San Mateo County: Tularemia Investigations

Entomology Report June 2008, San Mateo County Mosquito and Vector Control District

In response to a tularemia outbreak in primates housed in a facility in Portola Valley, the entomology staff have been investigating the role of possible vectors responsible for the disease transmission. Tularemia, also known as rabbit fever, is a potentially serious and highly infectious disease caused by a bacterium found in wild mammals, mainly rodents and rabbits. It can be transmitted to humans by a variety of means. Potential ways people can become infected include: ticks, biting flies, exposure to infected animal carcasses, eating or drinking contaminated food or water, or breathing in bacteria suspended in air. Symptoms of tularemia include: sudden fever, chills, headache, diarrhea, muscle aches, joint pain, dry cough, and weakness. This disease is treatable with antibiotics.

District staff have been examining the wildlife in the area to determine the cause of the outbreak. Burrowing ground squirrels are abundant near the facility and serve as a reservoir of infection. One group of vectors under investigation are horse flies in the family Tabanidae. These are large flies with a vicious and painful bite. They mainly feed on the blood of cattle and horses but will also attack humans and presumably other primates.

Two types of traps, a box trap and a malaise trap, were set out in the field to assess fly populations. Ground squirrels were trapped and blood samples were obtained to test for tularemia.