The following table contains the results of tests for evidence of Borrelia infection in ticks collected in California in 2008. The tests were conducted by the California Department of Public Health, Vector-Borne Disease Section (CDPH-VBDS), and by the United States Army Center for Health Promotion and Preventive Medicine - West (US Army).

Human granulocytic anaplasmosis (HGA) is an infection caused by the bacteria Anaplasma phagocytophilum. HGA bacteria infect the whte blood cells of their hosts, specifically a group of cells called granulocytes. People acquire HGA in California, when they are bitten with a western black-legged tick (Ixodes pacificus) infected with HGA bacteria.

Rocky Mountain spotted fever (RMSF) is a serious disease caused by Rickettsia rickettsii bacteria and transmitted to people by ticks, principally the Rocky Mountain wood tick, Dermacentor andersoni and the American dog tick Dermacentor variabilis. In California, RMSF is a rare disease, with only 1 to 3 cases reported per year; most cases are reported from the south Atlantic region of the United States.

Additional information on RMSF can be found at the Center for Disease Control and Prevention website:

Tickborne relapsing fever (TBRF) is a bacterial disease transmitted to people by soft ticks in the genus Ornithodoros. TBRF is a rare disease in California with between 1 and 8 cases reported per year, generally during the summer months. People are at risk of contracting TBRF when they sleep in rustic mountain cabins that are infested with wild rodents. The soft ticks that transmit TBRF feed rapidly; most people who contract TBRF have no recollection of a tick bite.

Ticks are the vectors of a large number of disease-causing agents in California. While Lyme disease is by far the most common tickborne disease of people in the United States and California, ticks also transmit the organisms that cause tickborne relapsing fever, Rocky Mountain spotted fever, tularemia, anaplasmosis, human ehrlichiosis, and babesiosis.  In addition, people and domestic animals can develop tick paralysis following a tick bite.

Click one of the following for the Vector-borne Disease Bulletins from the Vector-borne Disease Section, California Department of Public Health.

2007 May 2007: Vector-Borne Disease Bulletin June 2007: Vector-Borne Disease Bulletin September 2007: Vector-Borne Disease Bulletin     2008   February 2008: 2007 Summary Edition of the Vector-Borne Disease Bulletin April 2008: Vector-Borne Disease Bulletin August 2008: Vector-Borne Disease Bulletin October 2008: Vector-Borne Disease Bulletin   2009   February 2009: 2008 Summary Edition of the Vector-Borne Disease Bulletin April 2009: Vector-Borne Disease Bulletin September 2009: Vector-Borne Disease Bulletin

Lyme disease is a tickborne disease caused by the bacteria Borrelia burgdorferi.  It was first identified in California in 1978 from a Sonoma County hiker.  While incidence of Lyme disease (number of cases adjusted per population) is highest in the northwestern part of the state, human cases have been reported from many regions of California.

Vectorborne diseases in California having significant public health importance include infectious diseases whose pathogens are transmitted by, or in association with, mosquitoes, ticks, fleas, lice, and rodents. Pediculosis is a non-infectious disease that results directly from infestations of humans by lice, usually head lice.