LA County confirms first West Nile virus death of 2025

What is West Nile virus?

West Nile virus is a Flavivirus spread by certain species of mosquitoes.

It is currently the biggest mosquito-borne illness threat in California, and is endemic in the state, which means it’s always present in the environment as it cycles between mosquitoes and a wide variety of bird species. Cases are seasonal, usually beginning in early summer and continuing into the fall. During the 2024 season, 1466 cases of West Nile virus were reported throughout the United States with 1063 of them being severe. It's important to note that reported cases represent a small percentage of all the infections due to under-reporting, so West Nile virus is actually far more prevalent than these numbers reflect.

How does West Nile virus Spread?

West Nile virus is usually spread after a mosquito feeds on an infected bird and then bites a human. Some birds will die from the infection, while others will survive and amplify the virus, hence infecting more mosquitoes and also spreading it to other areas through travel and migration.  Humans don't usually produce enough of the virus in our system for mosquitoes to pick it up from us, that's why we are considered "dead-end hosts". West Nile virus is not spread person to person like a cold or flu might be, but it can be transmitted to a fetus during pregnancy or to an infant during breastfeeding. In rare cases, West Nile virus can be spread through blood transfusion or organ transplant. The United States blood supply does screen for West Nile virus and donors with a recent diagnosis of West Nile virus infection should not donate blood for 120 days. 

History:

West Nile Virus is an arbo-virus (arthropod-borne) that is commonly found in Africa, Asia, and the Middle East. It was first isolated from an adult woman in the West Nile District of Uganda in 1937, hence its name.  It is closely related to St. Louis encephalitis virus, which is also found in the United States, including California.  The virus is transmitted by mosquitoes and can infect humans, birds, horses, and other animals.

West Nile Virus in the United States

WNV was first identified in New York City in September 1999.  From 1999 through 2004, WNV quickly spread across the nation and has now been documented in every state and the District of Columbia except for Alaska and Hawaii.

Since 1999 over 51,000 confirmed human cases and 2,390 deaths have been reported across the United States.  Since its arrival in 2002 there have been almost 7,200 confirmed human cases and 320 deaths in California. 

The Antelope Valley first identified human cases of West Nile Virus in 2007, and has recorded many cases and several fatalities since then.

The most current map of WNV infections in California can be found at www.westnile.ca.gov.
For a current breakdown of cases/deaths by state, please refer to the Center for Disease Control and Preventions WNV website.
For current maps of WNV transmission in humans and animals, check out: http://diseasemaps.usgs.gov.

Symptoms of West Nile Virus:

No symptoms in most people:  Approximately 80 percent of people (about 4 out of 5) who are infected with WNV will not show any symptoms at all.
Milder symptoms in some people:  Up to 20 percent of the people (about 1 in 5) who become infected have mild symptoms beginning 2 to 15 days after the mosquito bite.  Symptoms such as fever, headache, and body aches, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back.  Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks and may even have lingering problems for years.
Serious symptoms in a few people: People who are immunocompromised or older than 50 years of age are at highest risk to develop a neuroinvasive form of West Nile virus.  About 1 in 150 people infected with WNV will develop severe neuroinvasive illness which involves imflammation of the brain (encephalitis) and/or of the tissue surrounding the brain and spinal cord (meningitis).  The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis and coma.  These symptoms may last several weeks, and neurological effects may be permanent. 1 in 10 people who develop this severe, neuroinvasive form of West Nile virus die.

Prevention:

There is currently no vaccine to protect against West Nile virus infection and there is no cure for the virus, just supportive treatment. Prevention of mosquito bites remains the ultimate West Nile virus prevention. People living in or travelig to areas with West Nile virus should protect themselves from mosquito bites by wearing long, loose-fitting clothing (mosquitoes can bite right through tight clothing) and by using a recommended repellent.

Follow the 3-D's to protect yourself from mosquito bites and West Nile virus:

Drain

• all standing water from in and around the home at least once a week - even small amounts of water can harbor hundreds of mosquito larvae.

Dusk and Dawn

• is the time when mosquitoes are most active, so that's when you need to avoid contact with them by staying indoors or following the guidelines below.

Defend yourself

• Wear repellent containing DEET, Picaridin, Oil of Lemon Eucalyptus, or IR3535 (see CDC recommendations). 
• Wear long sleeves and pants
• Install or repair window & door screens

Click HERE for a checklist of common mosquito sources. Look for them and eliminate them to help rid your yard and home of mosquitoes.

West Nile Virus Myths

-The Myth: Kids are at the most danger of getting sick from West Nile Virus.
-The Fact: People over 50 and those with other health issues (e.g. diabetes, high blood pressure) are at the highest risk for developing severe West Nile disease.

-The Myth: It's only people who are already in poor health that have to worry about West Nile Virus.
-The Fact: Young people and healthy, active adults who spend time working and exercising outdoors have also been affected by severe West Nile Virus infections. Personal protection measures remain important no matter your age or health status.

-The Myth: Repellents containing DEET are not safe.
-The Fact: DEET has been used for decades and is proven safe and effective when used as directed. Some people worry because it’s a “chemical,” but DEET has been carefully tested by the CDC and EPA and is safe for both adults and children (over 2 months old). It may smell strong, but it’s one of the best ways to prevent mosquito bites and disease. Always follow label directions closely.

-The Myth: As long as my area has a mosquito control program, I don't have to worry about using repellent.
-The Fact: Mosquito control activities don't eliminate every mosquito, so personal protection is still important.

Additional Information

Centers for Disease Control and Prevention - http://www.cdc.gov/westnile/index.html

California Department of Public Health - http://www.westnile.ca.gov

American Mosquito Control Association - https://www.mosquito.org/page/mosquitoinfo

Find current local West Nile virus detections HERE