West Nile Virus (WNV)

• It is a virus that can infect both people and animals
• Several species of animals can be infected by WNV, including: birds (especially crows), horses, and some reptiles
• WNV is an imported disease in the United States. In 1999, the first human and animal cases of WNV were found in New York City
• It appeared in Los Angeles County for the first time in 2003
• Since then, WNV infects people and animals every year in Los Angeles County

• Both people and animals get infected with WNV through the bite of an infected mosquito

In people

• Most people infected with WNV do not get sick, in some cases flu-like symptoms may develop (fever, headache, nausea). Very rarely, the virus can infect the brain and cause more severe symptoms.
• To know more about WNV infections in people.

In animals

• Birds - Most birds do not get sick from the virus, but may be able to infect mosquitoes that bite them. Crows, ravens and jays may become very ill and die rapidly after infection.
• Horses - WNV can cause severe neurologic signs in horses, such as: weakness, limb paralysis and death
• Dogs and cats - Dogs and cats rarely get sick from WNV
• Other - Tree squirrels can also get sick from the disease

• There is no specific cure for WNV infection
• Treatment in people is usually supportive

• Protect yourself from mosquitoes
  • Wear long-sleeve shirts when mosquitoes are most active, especially at dusk and dawn
  • Empty standing water around your house twice per week to stop mosquitoes from breeding
  • Use mosquito repellent
• Horse owners should vaccinate their horses

• Read about reporting individual dead birds for potential WNV testing.
• Read about reporting clusters of three or more sick or dead birds (or other animals) for potential testing.
• You can help monitor Los Angeles County for West Nile Virus. Whenever you see a dead bird, report it! Share this flyer about reporting dead birds in Los Angeles County (PDF)

Since its first appearance in Los Angeles County in 2003, WNV has caused infections in animals and humans every year. Monitoring WNV in birds can serve as an early-warning system for human infections:

• Birds typically begin to die from WNV before cases in humans appear
• Areas with high numbers of affected crows reflect higher risks of human infection

Maps of WNV in dead birds - multiple years

See the WNV dead bird data archive for maps and data from 2007-2019 (2014 - no map).

• 2019
• 2018
• 2017
• 2016
• 2015
• 2013
• 2012
• 2011
• 2010
• 2009
• 2008
• 2007

Data collection is based on passive reporting. Dead bird reports were received by VPH. Until 2013, dead crows were tested in-house; other bird species and squirrels were submitted to a different laboratory for testing. At this time, VPH is no longer able to test individual crows for WNV.

For current WNV activity in birds, see the California West Nile virus website and the WNV data on the ACDC West Nile virus page.