West Nile Virus has been detected in Los Angeles County for the first time this year, authorities said.

Three dead crows in the North Hills neighborhood tested positive for West Nile virus on May 26, according to the Greater Los Angeles County Vector Control District.

So far this year, there haven’t been any mosquito samples that have tested positive for the virus in the county or surrounding areas.

But surveilling dead birds serves as an early warning detection tool that helps authorities identify when the virus is actively being transmitted between birds in the area.

“American crows can fly up to 40 miles each day from overnight roosting sites, so while there has not yet been virus activity detected in mosquito populations in Los Angeles County, this confirmation serves as an alert that mosquitoes may soon become infected and residents should take precautions,” said Steve Vetrone of the Vector Control District.

West Nile virus is endemic to L.A. County, and it’s usually detected in the region during summer.

The virus is the leading cause of mosquito-borne disease in the U.S. and is transmitted to humans through the bite of an infected mosquito.

Last year, 17 people in L.A. County were infected with West Nile Virus, and 12 were hospitalized. One person died from a neuro-invasive disease associated with the virus in 2021, according to an L.A. County Department of Public Health.

The year before, the health department reported seven West Nile Virus deaths and 93 infections.

About 1 in 5 people infected with the virus will exhibit symptoms, which can include fever, headache, body aches, nausea or skin rash. The symptoms can last from days to months.

Severe West Nile virus infections can happen in some cases, especially in those over 50 with chronic medical conditions like cancer and diabetes. The infection can affect the brain and spinal cord, causing meningitis, encephalitis and paralysis.

About 1 in 150 people infected with the virus will require hospitalization. Severe symptoms include high fever, muscle weakness, neck stiffness, coma, paralysis and possibly death, officials said.

“Because there is no human vaccine for WNV, residents must be proactive against mosquito bites by wearing insect repellent,” officials said.

Most mosquitoes do not carry the virus, and most people bitten by mosquitos are not exposed to severe West Nile virus. Still, officials say L.A. County residents should take these steps to reduce the threat of the virus in their neighborhoods:

  • Eliminate standing water in clogged rain gutters, rain barrels, discarded tires, buckets, watering troughs or anything that holds water for more than a week.
  • Ensure that swimming pools, spas and ponds are properly maintained.
  • Change the water in pet dishes, bird baths and other small containers weekly.
  • Request mosquitofish from your local vector control district for placement in ornamental ponds.
  • Report neglected (green) swimming pools in your neighborhood to your vector control district.