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California West Nile Virus Home > 2004 Summary 4/5/05

West Nile virus activity was detected in all California counties in 2004 .

  • There were 830 human infections of WNV from 23 counties detected in California in 2004.
  • Sixty-six of these cases were first detected in asymptomatic individuals through screening done at blood banks - 15 later became symptomatic.
  • Of the 779 WNV cases with symptoms, 395 are classified as West Nile fever cases, 289 are classified as West Nile neuroinvasive disease, and 95 are of unknown status.
  • There have been 28 West Nile virus-related fatalities to date in California, in Glenn, Kern, Los Angeles, Orange, Riverside, San Bernardino, and Tehama counties.
Equines (Horses)
  • According to the California Department of Food and Agriculture, there have been 540 horse infections from 32 counties in 2004.
  • Of these West Nile virus infected horses, 228 have been euthanized or died.
Dead Birds
Mosquito Pools and Sentinel Chickens

  • 1,136 mosquito pools from 18 counties tested positive for WNV in 2004.
  • A mosquito pool is a collection of approximately 50 mosquitoes that are tested together for West Nile virus.
  • 809 chickens from 22 counties tested positive for WNV antibodies (seroconverted) in 2004.
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