The California Department of Public Health routinely tests various types of animals for evidence of infection by plague bacilli. The map displays data for 2004 for tests on carnivores, rodents, and pets.

Human granuocytic 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 Ornithodors. 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.

Malaria is not endemic to California. But on occasion, imported malaria resulted in local outbreaks. The map below illustrates those transmissions where 10 or more cases resulted.

As part of California's vector control efforts, samples from a variety of sources are regularly tested for the presence of West Nile virus, St. Louis encephalitis and Western equine encephalomyelitis. The map below is provided to illustrate the ongoing efforts to detect and control the these diseases. Use the layer checkboxes below the map to enable or disable the various layers.

• Autochthonous malaria:

  --- Indigenous. Mosquitoborne transmission of malaria in a geographic area where malaria occurs regularly.
  --- Introduced. Mosquitoborne transmission of malaria from an imported case in an area where malaria does not occur regularly.

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WNV Infection in Humans

St. Louis encephalitis virus (SLE), a member of the flavivirus family, was the most important mosquito-borne arbovirus in North America up until 1999, when West Nile virus (WNV) was introduced into the United States. Wild birds are the maintenance and amplifying hosts of SLE, which is transmitted among birds and to humans by primarily Culex mosquitoes. Human infection with SLE can result in mild to severe illness, with case-fatality rates ranging from 3%-30%.

Belgian soldiers digging trenches in World War I. Photo from firstworldwar.com