West Nile Virus

Vector Services & Information

Photo of a mosquito taking a blood meal



How do people and animals get West Nile virus?

West Nile virus is transmitted to people and animals (birds and horses) by infected mosquitoes. Only certain species of mosquitoes carry the virus and very few mosquitoes are actually infected.

Are there other ways of getting West Nile virus?

In rare instances, West Nile virus can be transmitted through blood transfusion, organ transplants, and from mother to fetus and breast feeding infants. Pregnant and nursing mothers are encouraged to avoid mosquitoes. Consult a physician for additional information.

What are the symptoms of West Nile Virus?

One in five persons infected with West Nile virus will exhibit symptoms. Symptoms usually occur between five and 15 days, and can include fever, headache, body aches, nausea, or a skin rash. These symptoms can last for several weeks to months. One in 150 people infected with the virus will require hospitalization. Severe symptoms include high fever, muscle weakness, neck stiffness, coma, paralysis, and possibly death.

Is there a vaccine for humans?

No, currently there is no WNV vaccination for humans.

Which animals get West Nile virus?

crowsAn infected mosquito can bite any animal, but not all animals will become infected. The disease most often affects birds (crows, ravens, magpies, and jays), but occasionally causes disease in other animals as well.

If you find a dead bird, particularly a crow or other corvid (i.e. raven, jay, or magpie) please call the California Department of Public Health hotline at 1-877-WNV-BIRD. Not all birds will qualify for testing, but they will record all reports of dead birds.

To move or discard a carcass, wear rubber or latex gloves. If gloves are not available, use a plastic bag turned inside-out over your hand and invert the bag to surround the bird. Seal and discard in the trash if the bird will not be picked-up for testing.

Horses are also susceptible to West Nile virus. The disease does not seem to be specific to a particular breed or age of horse. Many horses infected with West Nile virus will not develop any illness. Of those that do become ill, approximately 30% die or must be destroyed. If your horse becomes infected, it is not contagious to you or to other horses. Clinical signs can include a lack of coordination, stumbling, circling, falling, weakness or partial paralysis of limbs, muscle twitching (especially around nose and lips), an inability to rise, and grinding teeth. There are two different vaccinations available for horses. The timing of these vaccines is critical because they must be administered prior to disease exposure. Contact a veterinarian for advice.

Does West Nile virus affect dogs and cats?

Dogs and cats rarely show illness if infected with West Nile virus. The National Animal Poison Control Center warns that insect repellent should not be used on pets. Cats are highly sensitive to the chemicals, and both dogs and cats lick themselves and could ingest toxins from the repellents. So far, cats and dogs have been fairly resistant to the virus.

What are you doing to protect public health?

We use an Integrated Vector Management (IVM) strategy that combines scientific surveillance data, on-the-ground control efforts and public outreach activities. Our three major departments work together to share scientific and operational data. The data we collect and analyze direct our decisions to conduct neighborhood treatments, outreach or other activities to break West Nile virus transmission cycles in your neighborhood.

What can I do to help?

Since mosquitoes breed in standing water, you can help stop the mosquito life cycle and West Nile virus transmission by eliminating standing water on your property. Eliminate standing water by dumping or draining water in negelected swimming pools, ponds, rain barrels, discarded tires, buckets, or anything container capable of holding water for more than a few days. You can significantly contribute ot the fight against West NIle virus by following these simple actions. Remember, if they can't breed, they can't bite.

How to protect yourself and your family

  • Avoid activity at dawn and dusk when mosquitoes are most active
  • Apply mosquito repellent containing the active ingredient DEET when outside
  • Wear protective clothing (loose, light colored, long sleeve shirts and pants)

I'd like to present this information to a group. Do you have a PDF/Presentation file I can use?

The West Nile virus presentation file is available to all city officials, educators and media to use. Residents can also use the file to distribute to friends and family. This presentation is another tool GLACVCD provides to the public to help fight the spread of West Nile virus. You can download the file HERE.

I'd like more information. Where else can I look?

photo of PDF download

The California West Nile Virus website is a great resource for tracking WNV activity in the state (Click HERE). For more FAQs, download the PDF on the American Society for Microbiology Academy website (Click HERE).

Summary of WNV Positives For 2012

Humans 95/2 deaths 476/ 19 deaths
Horses 0 22
Dead Bird Surveillance 70 1,644
Mosquito Pools 318 2,894
Sentinel Chickens 26 540

Click here to view details on WNV activity for the year 2013

Summary of WNV Positives For 2011

Humans 44/2 deaths 158/ 9 deaths
Horses 0 15
Dead Bird Surveillance 159 688
Mosquito Pools 448 2,087
Sentinel Chickens 40 391

Summary of WNV Positives For 2010

Humans 1 111/6 deaths
Horses 0 19
Dead Bird Surveillance 31 416
Mosquito Pools 56 1,305
Sentinel Chickens 0 281

Summary of WNV Positives For 2009

Humans 8/1 death 112/4 deaths
Horses 0 18
Dead Bird Surveillance 38 515
Mosquito Pools 91 1,063
Sentinel Chickens 0 443

Summary of WNV Positives For 2008

Humans 83/15 deaths
443/21 deaths
Horses 0 32
Dead Bird Surveillance 259 2,569
Mosquito Pools 472 2,002
Sentinel Chickens 37 585

Summary of WNV Positives For 2007

Humans 32/3 deaths 378/16 deaths
Horses 0 28
Dead Bird Surveillance 115 1,395
Mosquito Pools 88 1,007
Sentinel Chickens 14 510

Summary of WNV Positives For 2006

GLACVCD Los Angeles County CA State
Humans 7/0 deaths 13/0 deaths 272/6 deaths
Horses 0 0 57
Dead Bird Surveillance 58 93 1,404
Mosquito Pools 78 78 833
Sentinel Chickens 18 38 640

Summary of WNV Positives For 2005

GLACVCD Los Angeles County CA State
Humans 22/0 deaths 47/0 deaths 935/18 deaths
Horses 5/3 deaths 10/6 deaths 456/200 deaths
Dead Bird Surveillance 135 173 3,044
Mosquito Pools 179 218 1,242
Sentinel Chickens 6 flocks (16 chickens) 77 793

Summary of WNV Positives For 2004

GLACVCD Los Angeles County CA State
Humans 180/4 deaths 331/14 deaths 830/28 deaths
Horses 8/5 deaths 16/8 deaths 540/230 deaths
Dead Bird Surveillance 645 840 3,232
Mosquito Pools 331 408 1,136
Sentinel Chickens 44 166 805

For more information on West Nile virus statistics, visit www.westnile.ca.gov.

District Programs

There are a number of Mosquito Species and Mosquito-Borne Diseases known to occur within the Greater Los Angeles County Vector Control District.

Click here to learn more.