UCLA Fielding’s Dr. Daniel Uslan on how to prevent West Nile virus

Cases of West Nile virus are on the rise in Los Angeles County, reaching their highest levels in nearly a decade, according to public health officials.

West Nile virus is a mosquito-borne illness. Birds are the primary hosts of the virus, explains Dr. Dan Uslan, an associate professor in the UCLA Fielding School of Public Health’s Department of Environmental Health Sciences and chief infection prevention officer for UCLA Health.

“It’s a bird-to-mosquito-to human cycle,” said Uslan, a board certified physician in internal medicine and infectious diseases.

Mosquitoes spread West Nile virus to humans by biting an infected bird and subsequently biting a person; the virus is commonly found in Africa, Europe, Asia, and North America, according to the World Health Organization.

There have been 100 reported cases of West Nile virus so far this year, the Los Angeles County Department of Public Health reported, adding that the county is on track for one of its most severe West Nile virus seasons since 2017. Five people have died.

For all last year, there were 22 cases and two deaths, according to Los Angeles County’s figures.

Most people - about 75% - who get infected with West Nile virus experience no symptoms and don’t get sick, Uslan said.

About 25% of people develop a syndrome called West Nile fever, a flu-like sickness with symptoms such as headache, fever, muscle aches and fatigue. It usually lasts for “a few days or a few weeks” and resolves on its own, he said.

A small number of people with West Nile fever will develop severe disease, in which the virus travels through the blood and infects the brain, Uslan said. In these cases, people may experience high fever, headache, confusion, coma and paralysis that can result in lifelong neurologic abnormalities even after recovering from the infection, he said.

Severe disease affects fewer than 1% of people infected, Uslan said.

Nearly all 100 West Nile cases reported countywide have caused serious illness requiring medical care, public health officials say. This is not surprising, they say, because most West Nile infections are asymptomatic and thus go unnoticed and unreported.

Those at highest risk for developing severe illness are adults older than 50 and people who are immunocompromised, Uslan said.

If you think you have West Nile fever, see your primary care doctor, Uslan suggests.

“There’s lots of other things circulating right around this time of year,” he said. “COVID is raging in Los Angeles County still, and we’re about to head into influenza season. A lot of these infections basically mimic each other and look very similar, so just because someone has a fever doesn’t mean they have West Nile.”

Preventing West Nile virus

There is no vaccine for West Nile virus, so the best way to avoid infection is to avoid mosquito bites, Uslan said. The virus is not transmitted from person to person.

He and public health officials advise:

• Use insect repellent. Repellents registered with the Environmental Protection Agency that contain DEET, picaridin, IR3535, 2-undecanone, and oil of lemon eucalyptus are the longest lasting and most effective, according to public health officials.
• Wear long sleeves and long pants outdoors, especially if you’re out at dawn or dusk, when mosquitoes are most active.
• Make sure the windows of your home are covered with well-fitted screens.
• Eliminate standing water around your home.

“Even very small amounts of standing water can provide a ground for mosquitoes to breed,” Uslan said. Look around outside your home and empty any flowerpots, pet dishes, saucers and watering cans that may have water in them.

Mosquito season lasts from June to November in Los Angeles County, and if it seems like there are more mosquitoes around than there used to be, it’s because there are. Different species of mosquitoes have come into southern California, Uslan said. Higher humidity this summer may have also extended the insects’ life spans.

Uslan notes that influenza kills many more people in Los Angeles County than West Nile virus, so he urges residents to get the flu vaccine. 

“People should check with their primary doctors about other vaccine-preventable diseases, especially with measles making a large comeback,” he said. “West Nile is certainly something to be concerned about, but not something to panic about.”