Skip to content
Slide Description
Slide Description

West Nile Virus


What is the West Nile virus and what should I do about it?

Para informacion en Espanol »

WNV Key Message Points - What can you do to protect yourself?

  • West Nile virus is transmitted by mosquito bites. It cannot be transmitted from person to person.

  • Avoid outdoor activity from dusk to dawn.

  • Dress appropriately during peak mosquito hours (wear long sleeves).

  • Use mosquito repellents containing DEET .

  • Drain pools of water and remove objects that can hold stagnant water (old tires).

Avoid Mosquito Bites to Avoid Infection

SOURCE: The Centers for Disease Control and Prevention

West Nile virus is spread by the bite of an infected mosquito, and can infect people, horses, many types of birds, and some other animals.

Most people who become infected with West Nile virus will have either no symptoms or only mild ones. On rare occasions, infection can result in a severe and sometimes fatal illness known as West Nile encephalitis (an inflammation of the brain). The risk of severe disease is higher for persons 50 years of age and older

West Nile Virus navigation links :

Protect yourself from mosquito bites

Avoid mosquito bites by applying insect repellent when spending time outdoors. Use repellent safely. Always read and follow product instructions. Human illness from West Nile virus is rare, even in areas where the virus has been reported. The chance that any one person is going to become ill from a mosquito bite is low.

You can further reduce your chances of becoming ill by protecting yourself from mosquito bites. To avoid mosquito bites, you can limit the number of places available for mosquitos to lay their eggs by eliminating standing water sources from around your home.

Apply insect repellent containing the active ingredient DEET, Oil of Lemon Eucalyptus, or Picaridin when outdoors, according to label instructions.

Use care in applying repellent to small children, and don't put repellent on their hands because it may get into their mouth or eyes and cause irritation. Whenever you use any insecticide or insect repellent, be sure to read and follow the product directions. For more information see Using Insect Repellent Safely from the EPA . Wearing long-sleeved clothes and long pants treated with repellent will further reduce your risk, as will staying indoors during peak mosquito feeding hours (dusk until dawn).

Check to see if there is an organized mosquito control program in your area. If no program exists, work with your local government officials to establish a program. The American Mosquito Control Association can provide advice, and their book Organization for Mosquito Control is a useful reference.

Back to Top

How to report dead birds

Dead birds in an area may mean that West Nile virus is circulating between the birds and the mosquitoes in that area. Over 230 species of birds are known to have been infected with West Nile virus. Although birds, particularly crows and jays, infected with WN virus can die or become ill, most infected birds do survive.

The State of California has created a hotline, 1-877-WNV BIRD(1-877-968-2473), to report birds that have been dead for less than 48 hours to have them picked up for testing for West Nile virus. You can also send an electronic notice to the state. The bird should show no signs of decomposition or maggot infestation. Birds such as crows, ravens, magpies, jays or hawks are the primary animals of concern. You can also watch a video on Reporting a Dead Bird on the website.

  1. Call the state hotline at 1-877-WNV-BIRD ( 1-877-968-2473) or visit: .

  2. There is no evidence that West Nile virus can be acquired from handling dead birds, but it is recommend you do not handle the bird with your bare hands.

  3. Place the bird in two plastic bags (double bag the bird) using gloves, a shovel, or by turning the bags inside out and collecting the bird.

  4. If you have found a dead bird on your property, and it has not been collected by 5 p.m. on the day of your report, you may safely dispose of it in your trash.

Back to Top

Questions and Answers

PLEASE NOTE: CDC is not a hospital or clinical facility; they do not see patients and are unable to diagnose your illness, provide treatment, prescribe medication, or refer you to specialists.

If you have a medical emergency, contacting CDC or the Stanislaus County Health Services Agency is not the proper way to get immediate help. In a medical emergency you should call 911.

Note: Not all Web site links are CDC or Stanislaus County Health Services Agency (HSA) sites and will be opened in a new browser window. CDC or HSA is not responsible for the content of Web pages found at these links. Links to nonfederal organizations are provided solely as a service to our users. These links do not indicate an endorsement of these organizations by CDC, the federal government or the HSA.

Back to Top

Avoid mosquito bites

Apply Insect Repellent Containing DEET
(Look for: N,N-diethyl-meta-toluamide) to exposed skin when you go outdoors. Even a short time being outdoors can be long enough to get a mosquito bite.

For details on when and how to apply repellent, see Insect Repellent Use and Safety in our Questions and Answers pages.

Back to Top

Clothing Can Help Reduce Mosquito Bites

When possible, wear long-sleeves, long pants and socks when outdoors. Mosquitoes may bite through thin clothing, so spraying clothes with repellent containing permethrin or DEET will give extra protection. Don't apply repellents containing permethrin directly to skin. Do not spray repellent containing DEET on the skin under your clothing.

Back to Top

Be Aware of Peak Mosquito Hours

The hours from dusk to dawn are peak mosquito biting times for many species of mosquitoes. Take extra care to use repellent and protective clothing during evening and early morning -- or consider avoiding outdoor activities during these times.

Back to Top

Mosquito-proof your home

Drain Standing Water
Mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by getting rid of items that hold water. Need examples? Learn more on the Prevention of West Nile virus Question and Answer page.

Back to Top

Install or Repair Screens
Some mosquitoes like to come indoors. Keep them outside by having well-fitting screens on both windows and doors.

Offer to help neighbors whose screens might be in bad shape.

Back to Top

Help your community

Report Dead Birds to Local Authorities
By reporting dead birds to state and local health departments, you can play an important role in monitoring West Nile virus. In California, if you see a dead bird you should call 1-877-WNV-BIRD or to send an electronic notice to the State go to

Back to Top

Mosquito Control Programs

Check with local health authorities to see if there is an organized mosquito control program in your area. If no program exists, work with your local government officials to establish a program. The American Mosquito Control Association can provide advice, and their book Organization for Mosquito Control is a useful reference.

More questions about mosquito control? A source for information about pesticides and repellents is the National Pesticide Information Center , which also operates a toll-free information line: 1-800-858-7378 (check their Web site for hours).

Back to Top

Clean Up
Mosquito breeding sites can be anywhere. Neighborhood clean up days can be organized by civic or youth organizations to pick up containers from vacant lots and parks, and to encourage people to keep their yards free of standing water.

Mosquitoes don't care about fences, so it's important to control breeding sites throughout the neighborhood.

Find out more about local prevention efforts
Find state and local West Nile virus information and contacts on the
Links to State and Local Government Sites page.

Source: Centers for Disease Control and Prevention

Back to Top

Route of West Nile virus

The most likely route of WNV infection to humans is through the bite of an infected mosquito. WNV may also be transmitted by organ transplantation, blood transfusion, or possibly breast milk [CDC 2002a,b]. Transplacental (mother-to-fetus) infection has occurred [CDC 2002c]. Laboratory-acquired infection has also been documented [CDC 2002d]. Turkey breeder farm workers have been infected with WNV [CDC 2003]. The mode of transmission to these farm workers is unknown.

Back to Top

Who is at Risk?

Most human WNV infections cause either no symptoms or a mild flu-like illness. The most severely affected patients may develop an inflammation of the brain, or the membranes of the brain or spinal cord, or both, called encephalitis, meningitis, or meningoencephalitis, respectively. These severe cases may be fatal. Persons over age 50 are at higher risk of severe illness following infection.

Back to Top  

Copyright © Stanislaus County, California 2023

Back to top