Case Counts by County
| County | Human cases | | Alameda | - | | Alpine | - | | Amador | - | | Butte | - | | Calaveras | - | | Colusa | - | | Contra Costa | - | | Del Norte | - | | El Dorado | - | | Fresno | 2 | | Glenn | - | | Humboldt | - | | Imperial | - | | Inyo | - | | Kern | 2 | | Kings | - | | Lake | - | | Lassen | - | | Los Angeles | 2 | | Madera | - | | Marin | - | | Mariposa | - | | Mendocino | - | | Merced | - | | Modoc | - | | Mono | - | | Monterey | - | | Napa | - | | Nevada | - | | Orange | - | | Placer | - | | Plumas | - | | Riverside | 2 | | Sacramento | 1 | | San Benito | - | | San Bernardino | 1 | | San Diego | - | | San Francisco | - | | San Joaquin | - | | San Luis Obispo | - | | San Mateo | - | | Santa Barbara | - | | Santa Clara | - | | Santa Cruz | - | | Shasta | - | | Sierra | - | | Siskiyou | - | | Solano | - | | Sonoma | - | | Stanislaus | - | | Sutter | - | | Tehama | - | | Trinity | - | | Tulare | - | | Tuolumne | - | | Ventura | - | | Yolo | - | | Yuba | - |
| Total | 10 |
| County | Horses | | 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 Clara | - | | Santa Cruz | - | | Shasta | - | | Sierra | - | | Siskiyou | - | | Solano | - | | Sonoma | - | | Stanislaus | - | | Sutter | - | | Tehama | - | | Trinity | - | | Tulare | - | | Tuolumne | - | | Ventura | - | | Yolo | - | | Yuba | - |
| Total | 0 |
| County | Dead birds | | Alameda | 7 | | Alpine | - | | Amador | - | | Butte | - | | Calaveras | - | | Colusa | - | | Contra Costa | - | | Del Norte | - | | El Dorado | 2 | | Fresno | - | | Glenn | - | | Humboldt | 1 | | Imperial | - | | Inyo | - | | Kern | - | | Kings | - | | Lake | - | | Lassen | - | | Los Angeles | 2 | | Madera | - | | Marin | - | | Mariposa | - | | Mendocino | - | | Merced | - | | Modoc | - | | Mono | - | | Monterey | - | | Napa | - | | Nevada | - | | Orange | - | | Placer | 1 | | Plumas | - | | Riverside | 2 | | Sacramento | 36 | | San Benito | - | | San Bernardino | - | | San Diego | - | | San Francisco | - | | San Joaquin | 1 | | San Luis Obispo | - | | San Mateo | 2 | | Santa Barbara | - | | Santa Clara | 6 | | Santa Cruz | 1 | | Shasta | - | | Sierra | - | | Siskiyou | - | | Solano | - | | Sonoma | - | | Stanislaus | 1 | | Sutter | - | | Tehama | - | | Trinity | - | | Tulare | - | | Tuolumne | - | | Ventura | - | | Yolo | 5 | | Yuba | - |
| Total | 67 |
| County | Mosquito samples | | Alameda | 7 | | Alpine | - | | Amador | - | | Butte | 4 | | Calaveras | - | | Colusa | - | | Contra Costa | - | | Del Norte | - | | El Dorado | - | | Fresno | - | | Glenn | - | | Humboldt | - | | Imperial | - | | Inyo | - | | Kern | 1 | | Kings | - | | Lake | - | | Lassen | - | | Los Angeles | 1 | | Madera | - | | Marin | - | | Mariposa | - | | Mendocino | - | | Merced | 1 | | Modoc | - | | Mono | - | | Monterey | - | | Napa | - | | Nevada | - | | Orange | 1 | | Placer | 4 | | Plumas | - | | Riverside | 9 | | Sacramento | 76 | | San Benito | - | | San Bernardino | 2 | | San Diego | - | | San Francisco | - | | San Joaquin | 55 | | San Luis Obispo | - | | San Mateo | - | | Santa Barbara | - | | Santa Clara | 1 | | Santa Cruz | - | | Shasta | - | | Sierra | - | | Siskiyou | - | | Solano | - | | Sonoma | - | | Stanislaus | 4 | | Sutter | - | | Tehama | - | | Trinity | - | | Tulare | 3 | | Tuolumne | - | | Ventura | - | | Yolo | 2 | | Yuba | - |
| Total | 171 |
| County | Sentinel chickens | | Alameda | - | | Alpine | - | | Amador | - | | Butte | - | | Calaveras | - | | Colusa | - | | Contra Costa | 7 | | 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 Clara | - | | Santa Cruz | - | | Shasta | - | | Sierra | - | | Siskiyou | - | | Solano | - | | Sonoma | - | | Stanislaus | - | | Sutter | - | | Tehama | - | | Trinity | - | | Tulare | - | | Tuolumne | - | | Ventura | - | | Yolo | - | | Yuba | - |
| Total | 7 |
WNV Activity by County
Printable Version
2018 |
2017 |
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2008
2007
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Data on this website are updated every Friday by 4pm. Due to different reporting schedules, case totals here may not always reflect those reported by local health departments. Updates during the off season (January-April) are less frequent.
April 17 - 23 is West Nile and Mosquito and Vector Control Awareness Week in California! This week highlights the importance of preventing mosquito bites and protecting Californians from mosquito-borne diseases. Stop by the "Fight the Bite" event at the State Capitol in Sacramento on Thursday, April 21st from 1:00 - 4:00pm for more information. Contact your local mosquito and vector control district to learn about events in your area.
- View Printable Map -
Total Counties with
WNV in 2018:
21
New counties highlighted in red.
Alameda, Butte, Contra Costa, El Dorado, Fresno, Humboldt, Kern, Los Angeles, Merced, Orange, Placer, Riverside, Sacramento, San Bernardino, San Joaquin, San Mateo, Santa Clara, Santa Cruz, Stanislaus, Tulare, and Yolo.
 | CDPH Confirms First Human West Nile Virus Illnesses of 2018
SACRAMENTO - The California Department of Public Health (CDPH) announced today the first confirmed illnesses in California due to West Nile virus (WNV). The four illnesses occurred in Los Angeles, Kern and Riverside Counties. "West Nile virus activity in the state is increasing, so I urge Californians to take every possible precaution to protect against mosquito bites," said CDPH Director and State Public Health Officer Dr. Karen Smith.
| | WNV Dead Bird Hotline Update
The West Nile virus and Dead Bird Hotline is staffed with live operators from 8AM to 4:30PM, Monday through Friday (later we will also be staffed on Sundays). Call the hotline at 1-877-WNV-BIRD to report a dead bird. Or fill out an online report form here:
Report a Dead Bird
Hotline operators will determine if the bird meets criteria for pickup and testing They will arrange for suitable dead birds to be picked up by a local vector control or public health agency for West Nile virus testing. Dead bird reports are very important because they are usually the first indication that the virus is active in an area, and this allows CDPH and local agencies to monitor the virus and implement control measures throughout the year.
Thank you for your report!
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- view news and press release archives -
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human cases YTD: 10 Counties: 6There was 1 new WNV human case reported in California this week from Fresno County. 10 human cases from 6 counties have tested positive for WNV in 2018.
horses YTD: 0 Counties: 0 No horses have tested positive for WNV in 2018.
dead birds YTD: 67 Counties: 13There were 17 new WNV positive dead birds reported in California this week from the following counties: Alameda (3), Placer (1), Sacramento (10), and Yolo (3). This is the first WNV positive dead bird from Placer County this year. 67 dead birds from 13 counties have tested positive for WNV in 2018.
mosquito samples YTD: 171 Counties: 15There were 65 new WNV positive mosquito samples reported in California this week from the following counties: Butte (4), Los Angeles (1), Placer (3), Riverside (3), Sacramento (33), San Joaquin (14), Stanislaus (4), Tulare (2), and Yolo (1). These are the first WNV positive mosquito samples from Los Angeles and Stanislaus counties this year. This is the first indication of WNV from Butte County this year. 171 mosquito samples from 15 counties have tested positive for WNV in 2018. A mosquito sample may contain up to 50 individual mosquitoes.
sentinel chickens YTD: 7 Counties: 1There were 7 new WNV positive sentinel chickens reported in California this week from Contra Costa County. This is the first indication of WNV from Contra Costa County this year. 7 sentinel chickens from 1 county have tested positive for WNV in 2018.
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Help us track down the West Nile Virus by reporting all dead birds. You can submit an online report by clicking on the button on the right.
| Element |
2003 |
2004 |
2005 |
2006 |
2007 |
2008 |
2009 |
2010 |
2011 |
2012 |
2013 |
2014 |
2015 |
2016 |
2017 |
Total |
| Human cases (fatal) |
31 (0) |
779 (29) |
880 (19) |
278 (7) |
380 (21) |
445 (15) |
112 (4) |
111 (6) |
158 (9) |
479 (20) |
379 (15) |
801 (31) |
782 (53) |
442 (19) |
553 (44) |
6,582 (292) |
| Horses |
12 |
540 |
456 |
58 |
28 |
32 |
18 |
19 |
15 |
22 |
13 |
03 |
03 |
03 |
21 |
1,223 |
| Dead birds |
96 |
3,232 |
3,046 |
1,446 |
1,396 |
2,569 |
515 |
416 |
688 |
1,644 |
1,251 |
2,442 |
1,349 |
1,352 |
510 |
21,952 |
| Mosquito samples |
32 |
1,136 |
1,242 |
832 |
1,007 |
2,003 |
1,063 |
1,305 |
2,087 |
2849 |
2,528 |
3,340 |
3,329 |
3,528 |
3,371 |
29,652 |
| Sentinel chickens |
70 |
809 |
1,053 |
640 |
510 |
585 |
443 |
281 |
391 |
540 |
485 |
443 |
449 |
343 |
305 |
7,347 |
| Squirrels |
- |
49 |
48 |
32 |
26 |
32 |
10 |
24 |
24 |
23 |
03 |
03 |
03 |
03 |
03 |
276 |
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1 There were 20 imported human cases.
2 There were 3 imported horse cases.
3 No longer monitored.
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Locate your local mosquito and vector control agency
Compared to previous year and previous five-year average to date
| As of Jul 13, 2018 | 2018 | 2017 | 5Y AVG |
| Counties | 21 | 22 | 28 |
| Human cases | 10 | 4 | 3 | | Dead birds | 67 | 72 | 307 | | Mosquito samples | 171 | 681 | 597 | | Sentinel chickens | 7 | 17 | 12 |
YTD - Year to date corresponds to the same time last year or last five years.
- view all 2018 YTD activity -
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WNV Reports
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