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%.

Malaria is no longer endemic in California. However, the disease is diagnosed in California residents every year, primarily as a result of contracting the disease in malarious areas outside the USA, and rarely, because of small focal outbreaks occurring as a result of importation of a case into an area when and where anopheline mosquitoes are prevalent.

 

Mosquitoes are primary vectors of serious infectious diseases in California. They transmit several arboviruses of public health importance, filarial worms causing dog heartworm, and sporadically and focally, human malarial parasites.

 

Photo credit Edman/McClelland collection