CA Dept. of Public Health UC Davis Arbovirus Research and Training Mosquito and Vector Control Assoc. of CA

Case Counts by County

CountyDead birds
Alameda-
Alpine-
Amador-
Butte-
Calaveras-
Colusa-
Contra Costa-
Del Norte-
El Dorado-
Fresno-
Glenn-
Humboldt-
Imperial-
Inyo-
Kern-
Kings-
Lake-
Lassen-
Los Angeles-
Madera-
Marin-
Mariposa-
Mendocino-
Merced-
Modoc-
Mono-
Monterey-
Napa-
Nevada-
Orange-
Placer-
Plumas-
Riverside-
Sacramento-
San Benito-
San Bernardino-
San Diego-
San Francisco-
San Joaquin-
San Luis Obispo-
San Mateo-
Santa Barbara-
Santa Clara3
Santa Cruz-
Shasta-
Sierra-
Siskiyou-
Solano-
Sonoma-
Stanislaus-
Sutter-
Tehama-
Trinity-
Tulare-
Tuolumne-
Ventura-
Yolo-
Yuba-
Total3

WNV Activity by County
Printable Version
2020 | 2019 | 2018
2017 | 2016 | 2015
2014 | 2013 | 2012
2011 | 2010 | 2009
2008 | 2007

Press Releases

Increasing West Nile Virus Activity in California

Californians Urged to Protect Against Mosquito Bites
Jun 26, 2019

SACRAMENTO - The California Department of Public Health (CDPH) urges all Californians to protect themselves from mosquito bites during West Nile virus (WNV) season, which extends from now through early fall.

"West Nile virus activity in the state is increasing, so it is important to take every possible precaution to protect against mosquito bites," said State Public Health Officer and CDPH Director Dr. Karen Smith.

West Nile virus spreads to humans and animals through the bite of an infected mosquito. Late-spring rains have contributed to standing water, which serves as a breeding source for mosquitoes that can spread WNV. Hot temperatures also contribute to increasing numbers of breeding mosquitoes and an increased risk of virus transmission to humans. Currently, WNV activity is within expected levels and is similar to activity at this time last year. The risk of disease due to WNV increases as the summer progresses, and declines in early fall as the weather cools. In 2018, there were 217 reported WNV cases in California, including 11 deaths. Since WNV was first introduced into California in 2003, there have been more than 6,000 human WNV cases and 303 WNV-related deaths across the state.

West Nile virus is influenced by many factors, including climate, the number and types of birds and mosquitoes in an area, and the level of WNV immunity in birds. For most people, the risk of developing serious illness is low. However, some individuals - less than one percent - can develop serious neurologic illnesses such as encephalitis or meningitis. People 50 years of age and older, and individuals with diabetes or hypertension, have a higher chance of getting sick and are more likely to develop complications from WNV infection.

CDPH recommends that people protect against mosquito bites and WNV by practicing the "Three Ds":

1. DEET - Apply U.S. Environmental Protection Agency (EPA)-registered insect repellent containing DEET, picaridin, oil of lemon eucalyptus, or IR3535 according to label instructions. EPA-registered repellents are recommended for use because they have been tested for safety and efficacy in preventing mosquito bites. Insect repellents should not be used on children under two months of age. For more information, visit CDPH's insect repellent toolkit.

2. DAWN AND DUSK - Mosquitoes that transmit WNV usually bite in the early morning and evening, so it is important to wear proper clothing and repellent if outside during these times. Make sure that your doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens that have tears or holes.

3. DRAIN - Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property by emptying flower pots, old car tires, buckets, and other containers. If you know of a swimming pool that is not being properly maintained, please contact your local mosquito and vector control agency.

California's West Nile virus website includes the latest information on WNV activity in the state. Californians are encouraged to report dead birds on the website or by calling toll-free 1-877-WNV-BIRD (968-2473).

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

As of Mar 20, 2020202020195Y AVG
Counties123
Human cases000
Dead birds314
Mosquito samples010
Sentinel chickens000
YTD - Year to date corresponds to the same time last year or last five years.

- view all 2020 YTD activity -

WNV Reports

Weekly Report

03.27 2020 YTD WNV Activity Map
03.06 2020 YTD SLEV Activity Map
03.04 2019 YTD WNV Activity Map

Humans

03.02 2019 Human WNV Incidence Report
03.02 2003-2019 WNV Case Summary
05.15 2018 Human WNV Incidence Report

Dead Birds

03.27Reported, Tested, Positive 2020
03.27Positive Species for 2020
03.27Positive Counts by City/County for 2020

Mosquitoes

10.04 AMOR - EVS Week 39
10.04 AMOR - GRAVID Week 39
10.04 AMOR - NJLT Week 39
- view report archives -