West Nile Virus

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Prevention
Current West Nile virus Activity
Historical West Nile virus Activity
Additional Information

About West Nile virus

West Nile virus (WNV) is a disease transmitted to humans, birds, horses, and other animals, by infected mosquitoes. Mosquitoes get the disease from feeding on infected birds. They can then bite and infect more birds or can bite and infect accidental hosts like people and horses. WNV can make people and horses sick and can even cause death.

WNV It is the most common mosquito-borne disease in the United States. It can be found in all 58 counties in California, including San Diego County.

Vector Control Program (VCP) staff monitor WNV by trapping, batching, and testing mosquitoes and by testing dead birds.

VCP also protects public health by controlling mosquitoes that can transmit WNV, which during the mosquito season includes aerial helicopter treatments of large bodies of water known to breed mosquitoes. The VCP also works to educate the public on measures they can take to keep themselves and their families safe from WNV and other mosquito borne diseases.

West Nile Virus Prevention

The Vector Control Program encourages everyone to prevent mosquito breeding, protect themselves against mosquito bites, and to report green pools, dead birds, and high mosquito activity. You can also request an educational inspection for your home, or a presentation about WNV prevention for your group or school.

Prevent

Dumping out standing water and keeping containers dry is easiest way to control mosquitoes around your home. Mosquitoes lay their eggs in standing water and can grow into biting adults in less than a week. You can dump water out or clean and replace the water. If you cannot dump the water, you can use a bacterial larvicide that comes in liquid, dunk, or granule form. Larvicides kill mosquitoes but are safe for people, plants, and animals. Make sure to follow the directions on the label. For larger artificial sources of water, like backyard ponds, birdbaths, fountains, animal troughs, unused swimming pools, you can add mosquitofish (available free of charge) to control mosquito larvae.

Protect

Avoid mosquito bites by wearing long sleeves and pants while outdoors and by using mosquito repellent. Keep screens over doors and windows closed and free of holes or gaps.

When choosing a repellent, look for an EPA-approved active ingredient like DEET, Picaridin, IR3535, Para-menthane-diol, 2-undecanone, or Oil of Lemon Eucalyptus.

Report

You can report to the Vector Control Program:

Green swimming pools that may be sources of mosquito breeding
Dead birds such as crows, jays, hawks, and owls (When appropriate these will be tested for WNV)
High mosquito activity, or other vector-related issue.

Current West Nile Virus Activity

2024 West Nile Virus Positives
Number of Positives to Date	Type	Date Collected	Location	Species
1	Bird	1/15/2024	Escondido	American Crow
2	Bird	2/29/2024	Escondido	Common Raven
3	Bird	9/6/2024	San Diego	American Crow
4	Bird	9/16/2024	San Diego - exact location unknown	American Crow
5	Bird	9/30/2024	Julian	California Scrub-Jay
6	Bird	10/22/2024	San Diego	American Crow
7	Bird	11/01/2024	Escondido	Cooper's Hawk

For human cases and statewide data visit the CDPH West Nile virus homepage.

Historical West Nile Virus Activity

Year	WNV Positive Mosquito Batches	WNV Positive Birds
2023	1	14
2022	0	0
2021	0	1
2020	2	1
2019	0	2
2018	3	1
2017	9	43
2016	99	266
2015	49	367
2014	2	41
2013	0	9
2012	0	1
2011	1	0
2010	1	2
2009	5	38
2008	40	563
2007	5	118
2006	0	19
2005	0	162
2004	0	34
2003	0	5