Beleaguered residents of the recent catastrophic Los Angeles fires are facing a new public health crisis: Mosquitoes.
It was a predictable outcome that has now come to fruition.
Abandoned and fire-damaged swimming pools in Los Angeles County, which is home to more than a quarter of a million swimming pools by the last count, are becoming a mosquito breeding hothouse.
The catastrophic January 2025 Los Angeles wildfires, including the Eaton, Pacific Palisades, and Hughes fires, killed 30 people as they burned through a combined total of about 47,894 acres, destroying more than 16,000 structures and damaging nearly 2,000 additional buildings.
And as these areas struggle to recover and rebuild, mosquitoes breeding in the rubble now pose an additional public health threat.
Officials are pointing fingers at the area’s abandoned swimming pools, where unknown numbers of pools have already become breeding grounds.
In the area that encompasses the Eaton fire, spokespersons have begun to sound the alarm.
The San Gabriel Valley Mosquito and Vector Control District, which covers Altadena, Pasadena, and Sierra Madre, reports that roughly 1,475 pools within the burn zone have been classified as “nonfunctional.” That means the pools are filled with stagnant water, filled with ash, debris, and broken equipment, or the homeowners are currently unable to maintain them.
Most of these pools are located in Altadena, where the district has treated half of these pools (mostly along the perimeter of the burn scar) with pesticides. The district expects to be able to treat the other half, but lacks funding for two follow-up treatments that officials say is necessary to prevent mosquito breeding for the rest of the year.
And the mosquitoes are gaining ground. In fact, in Altadena, the district has found mosquitoes breeding in about 80 percent of the roughly 700 pools that have so far been treated this year. And according to the Vector Control District for Los Angeles County, improperly maintained swimming pools can breed up to 3 million adult mosquitoes in just one month under the right weather conditions.
Photo credit: https://en.wikipedia.org/wiki/Mosquito Anais Medina Diaz, a spokesperson for the San Gabriel Valley Vector Control District, says that it is a public health concern that will become a “risk” if it doesn’t get addressed soon.
That’s because mosquitoes carry disease.
The primary threat is from West Nile Virus, which is considered endemic in the area, meaning it is consistently present in Los Angeles. According to the Los Angeles County Department of Public Health, 2024 saw 34 documented cases of West Nile Virus, including 27 hospitalizations and 2 deaths. The year before was even worse: 2023 brought a total of 70 cases and 3 deaths.
West Nile is spread by several species of Culex mosquitoes, which are common in California. (Culex mosquitoes make up the majority of the region’s mosquito population.) West Nile viral infections can manifest from no symptoms to mild, flu-like illness, and in rare cases, death.
Dengue is also a concern. Until recently, almost all reported cases of dengue in Los Angeles County have involved travel to another country, but in 2024, the county’s public health dept. reported 14 cases of locally acquired dengue, which is spread by the invasive Aedes mosquitoes (not native to California but currently found in at least 28 counties, including Los Angeles). The state’s first known case of locally acquired dengue occurred in Pasadena in 2023. Prior to that, dengue had been confined to tropical and subtropical areas of Central and South America, Southeast Asia, the Pacific Islands, and the Caribbean.
Dengue is commonly accompanied by eye, muscle, and joint pain and fever typically lasting up to a week and, rarely, death.
In the area affected by the Eaton fire, vector control officials began treating the first half of abandoned swimming pools with pesticides in mid-March, with treatments expected to last until mid-June, which will coincide with the height of the mosquito season.
Also in March, the California Governor’s Office of Emergency Services approved additional funds to treat the other half of the area’s swimming pools, but the funds for the necessary follow-up treatments have not yet been approved. Things look slightly better in the Pacific Palisades area, where officials don’t anticipate budgeting issues will affect its mosquito treatment plans.
Southern California’s outdoor workers will be wise to take extra precautions to avoid mosquito bites this season. You can take steps to keep mosquitoes from biting you and your family, such as wearing long sleeves and using insect repellent that contains the following active ingredients:
• DEET (chemical name: N,Ndiethyl- m-toluamide or N,N-diethyl-3-methyl-benzamide).
• Picaridin (KBR 3023 [Bayrepel] and icaridin outside the US; chemical name: 2-(2-hydroxyethyl)1-piperidinecarboxylic acid 1-methylpropyl ester).
• Oil of lemon eucalyptus (OLE) or PMD (chemical name: para-menthane-3,8-diol),thesynthesizedversionofOLE.
This recommendation refers to EPA-registered products containing the active ingredient OLE (or PMD). “Pure” oil of lemon eucalyptus (essential oil not formulated as a repellent) is not recommended; it has not undergone similar, validated testing for safety and efficacy and is not registered with EPA as an insect repellent.
• IR3535 (chemical name: 3-[ N- butyl- N- acetyl]aminopropionic acid, ethyl ester). 2-undecanone (chemical name: methyl nonyl ketone).
