This fall in Los Angeles, mosquitoes are buzzing, leaving people with itchy marks and transmitting the West Nile virus.

Richard Dang, an associate professor of clinical pharmacy, discussed the recent increased prevalence of mosquitoes.

“The Los Angeles County Department of Public Health released a recent notice that we’re experiencing the highest number of West Nile virus cases in nearly a decade,” Dang said.

According to a West Nile virus health alert issued by the USC Office of Environmental Health and Safety, the number of people infected with West Nile in 2026 has surpassed the five-year average “during the same period of time.” It reports that “mosquito pools and dead birds are testing positive across many areas of LA County.”

“Mosquitoes by themselves don’t carry the virus,” Dang said. “They have to pick up the virus from other animals, primarily birds. As birds are infected, mosquitoes are eating the dead birds who may be sick; that’s how the mosquitoes pick up the virus.”

Dr. Sarah Van Orman, USC’s chief campus health officer, reassured that most people who are bitten by mosquitos are going to be “just fine.”

Dang said that West Nile virus is a fairly asymptomatic disease that does not lead to serious symptoms for most people, which would usually include general common cold symptoms and potential fever.

“But there are some individuals who are at higher risk for more serious diseases, and that’s who we are primarily concerned about when we see an increase in West Nile virus cases,” Dang said. “That primarily includes those who [are] elderly or those who might have other chronic medical conditions, like diabetes, asthma or other diseases. … Some of these serious illnesses can develop into things like meningitis, or even in more serious cases, death.”

The increasing heat and humidity could be key to understanding the rise in mosquitoes and, as a result, West Nile virus cases. Orman said that due to climate change, “the historic ranges” of mosquito-related diseases are changing.

“Mosquitoes love being in warm environments, and we are experiencing an unusually warm and moist summer and fall season,” Dang said. “It’s the prime breeding ground for mosquitoes to grow and expand their population. As we have more mosquitoes, we’re having more mosquito bites. As there [are] more mosquito bites, we see more mosquito-related diseases, including West Nile virus.”

Both Orman and Dang advised wearing long, protective clothing and using mosquito repellent.

“Check your living environment, if you are living somewhere where you leave your windows open, [or] have screens.” Orman said. “I know a lot of students are renters, so they may not be as aware of the conditions of their windows. But check those screens, make sure they’re on tight, make sure there aren’t gaps in places that mosquitoes can enter.”

A news release published by L.A. County Public Health on Sept. 21 urged people to take immediate steps to prevent the spread of mosquito-borne illnesses.

“Prevention is definitely key,” Dang said. “There are currently no treatments or vaccines for West Nile virus, and so knowing that West Nile virus is spread primarily by mosquito bites, we’re looking at ways to prevent these mosquito bites from happening.”

Standing water is also a threat. The Centers for Disease Control and Prevention informs that mosquitoes lay eggs near water, leading to increased breeding.

“They’re very adapted to urban life,” Orman said. “We say they grow in standing water, but by ‘standing water,’ it can [even] be a bottle cap.”

Dang recommended that people look around their households and properties for any standing water in pots or puddles and remove it as soon as possible.

“If water has been there for more than a few days, that’s the perfect breeding ground for mosquitoes to lay their eggs and more mosquitoes to come around,” Dang said.

Using bug spray is also an option. Dang recommended insect repellents like DEET or picaridin that can be applied to the skin, and create a barrier to discourage contact with mosquitoes. Additionally, Orman said a mosquito control program is present on campus, and the USC Environmental Health and Safety team monitors, traps and sprays.

“We’re probably going to continue to see an increase in mosquitoes and their related diseases,” Dang said. “Based on what I’ve seen for prediction on future climate, we’re expecting it to get hotter and more humid.”