Peak mosquito season is here, and with the passing of Tropical Storm Hilary over the West Coast last month, there are at least double the number of invasive mosquitoes buzzing around Los Angeles County compared to the previous year.
That’s the approximation given by Susanne Kluh, the general manager of the Greater LA County Vector Control District (GLACVCD) — a public health agency that provides ongoing mosquito and vector control for its residents. GLACVCD covers 36 cities and unincorporated portions of LA County, including the City of San Fernando, Santa Clarita and Burbank.
There are two main species of mosquitoes in the LA county area: the southern house mosquito, also known as culex quinquefasciatus, and the invasive yellow fever mosquito, otherwise known as aedes aegypti.
The southern house mosquito is the main vector for the outbreaks of West Nile virus in Southern California. As of press time, there have been 25 infections in LA County with one fatality, according to the LA County Department of Public Health. This is less than half the number of infections last year at 64 and far below the record high of 309 back in 2004.
Although there are more mosquitoes this season in general, Kluh said they’ve been able to keep the southern house mosquito population in check by connecting to residents and making sure they empty out their swimming pools and telling them to get rid of any sources of standing water, including buckets and pots, where mosquitoes can breed.
“We saw some higher numbers earlier in the year, but by the time we got to July and August, we were back to our five-year average,” Kluh said. “For us, it hasn’t been a bad year for West Nile virus. The number of human cases that the Health Department has reported so far, while we regret every single one of them, have not been concerningly high and below last year. … It’s been a pretty mild year. We’re really happy with our results.”
There is, however, the issue of the extra water brought on by Hilary, refilling once empty swimming pools. Although Kluh said she doesn’t anticipate a late increase in West Nile infections, she still encourages any Angeleno who emptied their pool before to drain them again.
An issue that is of concern is the prevalence of the yellow fever mosquito, an invasive species that is found all over the world. Coming to the United States around 2014, they have since spread across the nation. These mosquitoes are known to spread the Zika virus, chikungunya, dengue fever, and, as their name would suggest, yellow fever.
And they are very difficult to control and are more prone to biting than southern house mosquitoes.
“They lay these durable eggs that can be valid for at least a year or longer,” Kluh said. “They can stay dry, and when you put water back into the same container where the eggs are laid, they will hatch a long time later. That’s how they easily get transported around the world.”
Kluh said that yellow fever mosquitoes love biting people exclusively and they can lay their eggs in small amounts of water, including bottle caps and leftover water in ice chests. The combination of the water brought in by Hilary and the increased warmth has caused these mosquitoes to go through their life cycles quicker and created a humidity where they can live longer.
This creates a problem, Kluh said, when people are returning from their summer vacation to tropical destinations where these viral infections are endemic and they get bitten by a yellow fever mosquito. That mosquito could then spread the infection to more and more people.
Kluh said that they have not found any evidence of that happening yet, but they are still monitoring any travel-related cases closely.
“With West Nile, it needs a lot of positive mosquitoes before we see human cases. With dengue, very few infected mosquitoes [are needed] to spread this around the neighborhood, potentially,” Kluh said. “We’re not hopeful that we would find a positive mosquito [for dengue] before the Health Department would find a case that didn’t actually travel anywhere.”
Kluh said that those returning from tropical destinations should wear mosquito repellant more frequently for 10 to 12 days once back home. Although she estimates that 80 percent of those with dengue fever are asymptomatic, other viral infections — including chikungunya — have much higher rates of people showing symptoms, which could cause a hit to the economy if more and more people got sick.
Furthermore, of the viral infections that yellow fever mosquitoes can spread, only the one that it’s named after has a vaccine available against it. There are also no treatments for Zika, dengue or chikungunya.
To try and combat this problem, GLACVCD is working with the Orange County Vector Control District on a program to sterilize male mosquitoes by exposing them to radiation. The hope is that by capturing and releasing sterilized mosquitoes, the overall population of mosquitoes will decrease.
“[The program] is in its infancy, but we’re really hoping that this will be a major tool in our toolbox,” Kluh said. “While it’s going to be a long time before that can go countywide, we were hoping that we can at least identify high-risk areas for a potential outbreak of one of these tropical diseases and then start using this new control method in some of those areas.
“We’ll have to see how easy it is to scale that because it’s going to need a lot of male mosquitoes.”
To keep Angelenos safe, Kluh urged that residents get rid of any water source on their property. She said mosquitoes tend not to fly far, so if residents find a bunch of mosquitoes buzzing around, look around the yard and talk to neighbors about where a potential source may be. If they need help identifying a source, they can submit a service request to GLACVCD and someone can be sent out to help look, as well as provide any necessary information.
It’s also recommended that you keep wearing long-sleeved shirts and long pants when outdoors, ensure your windows and door screens are still effective and use insect repellent that contains DEET, picaridin, oil of lemon eucalyptus or products that contain IR3535 during dusk or dawn when southern house mosquitoes are most active.
For more information about GLACVCD or to submit a service request, go to https://www.glamosquito.org/. To learn more about insect repellants and choose the right one for you, go to https://www.epa.gov/insect-repellents/find-repellent-right-you.