Case Counts by County

CountyDead birds
Alameda12
Alpine-
Amador-
Butte33
Calaveras-
Colusa3
Contra Costa4
Del Norte-
El Dorado2
Fresno1
Glenn4
Humboldt2
Imperial-
Inyo-
Kern1
Kings3
Lake5
Lassen-
Los Angeles12
Madera1
Marin3
Mariposa-
Mendocino-
Merced1
Modoc-
Mono-
Monterey-
Napa5
Nevada9
Orange25
Placer8
Plumas-
Riverside39
Sacramento61
San Benito-
San Bernardino4
San Diego107
San Francisco-
San Joaquin11
San Luis Obispo-
San Mateo8
Santa Barbara-
Santa Clara83
Santa Cruz-
Shasta10
Sierra-
Siskiyou-
Solano7
Sonoma4
Stanislaus13
Sutter16
Tehama-
Trinity2
Tulare22
Tuolumne-
Ventura6
Yolo48
Yuba6
Total581

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 Aug 28, 2015201520145Y AVG
Counties403632
Human cases8312554
Dead birds5811573751
Mosquito samples207324841702
Sentinel chickens174184151
YTD - Year to date corresponds to the same time last year or last five years.

- view all 2014 YTD activity -

WNV Reports

Weekly Report

08.28 Arbovirus Bulletin #26
08.28 2015 YTD WNV Activity Map
08.25 2015 US Arboviral Activity Update

Humans

08.28 2015 Human WNV Incidence Report
08.28 2003-2015 WNV Case Summary
03.09 2014 Human WNV Incidence Report

Dead Birds

08.28Positive Species for 2015
08.28Positive Counts by City/County for 2015
08.28Reported, Tested, Positive 2015

Mosquitoes

08.28 AMOR - EVS Week 33
08.28 AMOR - GRAVID Week 33
08.28 AMOR - NJLT Week 33
- view report archives -