These days, mosquitos are a common concern for those living in Southern California. And they’re definitely affecting people’s ankles.
The insects have become a year-round nuisance in the area, but as summer approaches, their presence really spikes, making outdoor gatherings, like barbecues, even more frustrating.
However, it’s not just the annoyance; their impact on public health is quite significant.
West Nile virus is spreading across the U.S. at rates not seen in nearly 20 years, according to federal health officials. In Southern California, scientists note an uptick in mosquitos carrying the virus, which is transmitted by a local species.
At the same time, another invasive mosquito species, Aedes aegypti, is rapidly increasing in number. This species can transmit several diseases, including dengue fever, Zika, and yellow fever.
In response, vector control teams are releasing millions of modified mosquitos to help manage their overall populations.
West Nile Virus
According to the California Department of Public Health, West Nile virus is the most common and severe mosquito-borne illness in the state.
This summer, Southern California is seeing more mosquitos testing positive for West Nile than usual. Data indicates that in June, the number of infected mosquitos reached levels typically seen much later in the summer.
It’s still uncertain if this increase will lead to more human cases. So far, only two cases have been reported this summer—one in Antelope Valley and another in Long Beach.
“Seeing two cases at this stage isn’t really unexpected. We are in July,” said Dr. Aiman Halai from the Los Angeles County Department of Public Health. “Mosquito activity increases around May and lasts until late fall, so human cases typically emerge during this period.”
Over the last five years, L.A. County has averaged about 41 West Nile virus cases annually. However, many infected individuals may not exhibit any symptoms at all.
When symptoms do appear, they range from fever and body aches to more severe issues like brain inflammation and paralysis. The virus attacks the central nervous system, making older adults and those with existing health problems more vulnerable, and there’s no vaccine or treatment available at this time.
Aedes aegypti
West Nile virus is spread by a local mosquito species known as Culex quinquefasciatus, or the southern house mosquito, which primarily feeds on birds but will also bite humans.
Unlike West Nile, other diseases carried by Aedes aegypti can be transferred directly from human to human. This invasive species has thrived in Southern California for over a decade, even causing an outbreak of dengue fever in L.A. County not long ago.
“The local transmission of dengue was concerning, and we want to prevent that from happening again,” said Steve Vetrone from the Greater Los Angeles County Vector Control District.
Dengue symptoms include fever, body aches, and rashes, affecting about one in four infected individuals, and can escalate into severe cases leading to shock and internal bleeding.
This mosquito species also poses risks for the transmission of Zika and yellow fever.
Sterilized Insect Technique
Authorities are employing a variety of methods to keep mosquito populations in check.
Some effective strategies involve eliminating standing water where mosquitos breed, whether it’s from natural sources or water pooling in garden pots. They sometimes use satellite imagery to locate neglected pools that are potential breeding grounds.
In desperate situations, they apply pesticides and treat areas like gutters and underground drains.
A new approach is the Sterilized Insect Technique (SIT), targeting Aedes aegypti specifically. This method involves releasing sterilized male mosquitos, which can’t reproduce, thanks to a specific virus or radiation.
Once introduced into the environment, these males mate with females, but no viable offspring result, eventually reducing the mosquito population.
The San Gabriel Valley Vector Control District started its SIT program this summer, releasing about 30,000 sterilized mosquitos weekly in Bassett Park and its surroundings, with plans for nearly 500,000 by October’s end.
“These invasive species have taken hold in nearly every city across our district,” noted Tristan Hallum, a scientist in the district. “We’re trying to find the best ways to ease the discomfort for our residents.”
A similar initiative began in Sunland-Tujunga last year, with Orange County focusing its efforts in Mission Viejo.
“People are pleased with the noticeable decrease in mosquitoes,” Miquel Jacobs from the Orange County Vector Control District said.
Yet, while these SIT programs show promise, they are still in the testing phase. It’s unclear if they can be expanded effectively.
In the meantime, officials stress the importance of removing standing water where mosquitos can breed.
