Case Counts by County

CountyDead birds
Alameda5
Alpine-
Amador-
Butte17
Calaveras-
Colusa3
Contra Costa2
Del Norte-
El Dorado1
Fresno-
Glenn3
Humboldt2
Imperial-
Inyo-
Kern1
Kings1
Lake2
Lassen-
Los Angeles3
Madera1
Marin1
Mariposa-
Mendocino-
Merced1
Modoc-
Mono-
Monterey-
Napa-
Nevada1
Orange5
Placer4
Plumas-
Riverside16
Sacramento27
San Benito-
San Bernardino1
San Diego65
San Francisco-
San Joaquin7
San Luis Obispo-
San Mateo7
Santa Barbara-
Santa Clara49
Santa Cruz-
Shasta3
Sierra-
Siskiyou-
Solano4
Sonoma3
Stanislaus8
Sutter10
Tehama-
Trinity1
Tulare18
Tuolumne-
Ventura2
Yolo23
Yuba4
Total301

WNV Activity by County
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2015 | 2014 | 2013
2012 | 2011 | 2010
2009 | 2008 | 2007

Press Releases

EARLY ONSET OF WARM WEATHER TRIGGERS AN EARLY WEST NILE VIRUS SEASON

Apr 23, 2007

SACRAMENTO - Unusually high temperatures throughout the state in March triggered an earlier than normal start to the West Nile virus (WNV) season, State Public Health Officer Dr. Mark Horton warned today.

"Mosquitoes that carry West Nile virus are breeding earlier this year due to warm weather," Horton said. "While no predictions can be made about the severity of West Nile virus this season, Californians should begin taking precautions to protect themselves from mosquito bites by eliminating all sources of standing water that can support mosquito breeding and applying insect repellent containing DEET."

WNV was first detected in California five years ago. So far this year, no human cases of WNV have been identified. However, the virus has been detected in mosquito pools, sentinel chickens or horses in eight counties: Imperial, Los Angeles, Orange, Riverside, Santa Clara, San Diego, Sonoma and Stanislaus.

In 2006, a total of 292 human WNV infections, including seven deaths, were reported in the 54 counties that detected WNV activity. Of the 58 horses that also tested positive for WNV, 24 died or were euthanized. WNV is transmitted to humans and animals through a mosquito bite. Mosquitoes become infected when they feed on infected birds.

Governor Arnold Schwarzenegger has invested a total of $15 million over the last two years to enhance mosquito control efforts. This funding has supplemented the resources of existing mosquito control programs statewide and expanded efforts in areas of the state not covered to combat WNV. This investment in equipment and other products to control mosquitoes continues to benefit mosquito control efforts this year.

Horton reminded Californians of three simple ways to protect themselves from WNV:


  • DEET - Apply inspect repellent containing DEET, picaradin or oil of lemon eucalyptus according to label instructions. Repellents keep the mosquitoes from biting you. DEET can be used safely on infants and children 2 months of age and older.

  • DAWN AND DUSK - Mosquitoes that carry WNV bite in the early morning and evening so it is important to wear repellent at this time. Make sure that your doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens with tears or holes.

  • DRAIN - Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property, including flower pots, old car tires, rain gutters and pet bowls. If you have a pond, use mosquito fish or commercially available products to eliminate mosquito larvae.

California's WNV Web site - www.westnile.ca.gov - has been updated to make it easier for the public to find the latest information on WNV activity in the state. In addition to reporting all dead birds, Californians are encouraged to report dead tree squirrels, three types of which have tested positive for WNV in California: the Western Gray, Fox and Eastern Gray. The Web site also includes information on the most common birds found with WNV. Dead birds and squirrels can be reported on the Web site or by calling (877) 968-2473.

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Compared to previous year and previous five-year average to date

As of Jul 31, 2015201520145Y AVG
Counties363527
Human cases8187
Dead birds301875386
Mosquito samples1058977641
Sentinel chickens453938
YTD - Year to date corresponds to the same time last year or last five years.

- view all 2014 YTD activity -

WNV Reports

Weekly Report

07.31 Arbovirus Bulletin #22
07.31 2015 YTD WNV Activity Map
07.28 2015 US Arboviral Activity Update

Humans

07.29 2015 Human WNV Incidence Report
07.29 2003-2015 WNV Case Summary
03.09 2014 Human WNV Incidence Report

Dead Birds

07.31Positive Species for 2015
07.31Positive Counts by City/County for 2015
07.31Reported, Tested, Positive 2015

Mosquitoes

07.31 AMOR - EVS Week 29
07.31 AMOR - GRAVID Week 29
07.31 AMOR - NJLT Week 29
- view report archives -