Experts say climate change is increasing the risk of potentially dangerous mosquito-borne diseases in California — threatening to turn those annoying but harmless bites into serious illnesses.
California is already struggling with West Nile virus, a potentially fatal disease It was first found in the state about two decades ago. But officials are now warning about a potential new enemy: dengue, a viral infection that can be life-threatening in the most severe cases.
Until last year, all dengue cases reported in California were linked to people traveling to a country where the disease is common. But Los Angeles County public health officials are now warning about “unprecedented” local transmission of dengue, which is commonly found In tropical and subtropical climates.
Just this month, the county public health department reported four cases of locally acquired dengue — meaning people were infected in their own communities, not while traveling. Three were documented in the San Gabriel Valley city of Baldwin Park; The latest incident was reported Wednesday in Panorama City, about 30 miles to the northwest.
“Although the widespread prevalence of dengue is low, we urge residents to take simple steps to reduce exposure to mosquitoes. These include using insect repellent to prevent mosquito bites,” LA County Public Health Director Barbara Ferrer said at a recent news conference.
Dengue, the world’s most common mosquito-borne disease, is not spread directly from insect to insect. According to Jason Farned, district manager of the San Gabriel Valley Mosquito and Vector Control District, mosquitoes pick up the virus after biting an infected person, then spread it by biting others.
The concern, however, is that “if there are enough infected mosquitoes, it can spread rapidly,” said Dr. Aiman Halai, director of the L.A. County Department of Public Health’s Vector-Borne Disease Unit.
“When we see local cases here, we really want to act on them quickly, identify if there are additional cases in that area, and use our vector-control to rapidly control the mosquito population.” “We want to work with partners to keep this from spreading.” Halai said.
Authorities are hoping to eliminate local reservoirs of dengue by reducing mosquito populations and eliminating potential breeding sites, namely containers holding water.
Last October, officials announced first confirmed case Dengue in California not linked to travel – in one resident PasadenaAnother locally acquired case reported long Beach After about two weeks.
West Nile virus was first documented locally A generation ago, in 2003.
Experts say climate change is contributing to the spread of these invasive, non-native mosquito-borne diseases. World Health Organization warned last year Global warming “could lead to higher average temperatures, rainfall and longer periods of drought, leading to record numbers of dengue infections worldwide.”
America Environmental Protection Agency It has also been said that climate change increases the risk of exposure to West Nile virus, as warmer temperatures can accelerate mosquito growth, biting rates and the ability of the disease to thrive within the insect. Mild winters and drought have also been linked to West Nile virus outbreaks, the EPA said.
it was only about a decade ago that invasive mosquito species aedes aegypti Was first found in California, shocking officersThat species can transmit dengue, as well as other viruses, namely yellow fever. aedes aegypti Was found in the Central Valley in 2013 and in Los Angeles County next year,
aedes aegypti It has now been identified throughout Southern California, including San Diego, Orange, Riverside, San Bernardino, Ventura and Imperial counties; As well as in Sacramento, Fresno and Kern counties.
The species has also been found in Butte, Shasta and Glenn counties in the north, according to California Department of Public HealthAt least three counties in the San Francisco Bay Area – Santa Clara, Contra Costa And solano – have got it aedes aegypti This year.
In form of California Office of Environmental Health Hazard Assessment notes, “A changing climate may create favorable conditions for invasive mosquito species to expand their geographic range into California.”
aedes aegypti It is considered more likely than other types of Aedes mosquito, aedes albopictus, To spread viruses like dengue, according to US Centers for Disease Control and Prevention. aedes albopictus, Also known as Asian tiger mosquitoes, arrived in LA County in 2001 and there have been an unusual number of complaints about them ever since. aggressive, daytime biter,aedes aegypti Bites even during the day.)
Besides California, other states that have reported limited local spread of dengue are Texas, Florida, Arizona, and Hawaii. Health officials in Puerto Rico announced dengue outbreak in March.
“Dengue cases have increased dramatically around the world in recent decades,” WHO says. The number of cases reported globally is expected to increase from about 500,000 in 2000 to more than 6.5 million in 2023, a record.
“Dengue is at record highs around the world,” Farnad said. “And so, as dengue infections are higher in other places in the world (and) among people who are traveling in and out of L.A. County, there is an increased risk that someone could bring the virus back and spread it to our local Might get bitten by one of the mosquitoes.”
Officials say dengue cases are underreported because most are asymptomatic or have mild symptoms.
But mosquito-borne disease is not toothless. About 1 in 20 people who become infected with dengue will become seriously ill, suffering shock, internal bleeding, organ loss or respiratory failure.
People at highest risk for serious illness include children, pregnant people, seniors age 65 and older, and people with certain medical conditions.
More than 7,300 deaths from dengue were recorded globally in 2023.
“Any infection can cause serious illness,” Halai said.
Other possible symptoms include high fever, severe headache, pain behind the eyes, joint and muscle pain, rash, and bleeding.
Severe dengue is a medical emergency, and people with the following symptoms should go to the emergency room immediately: abdominal pain or tenderness, vomiting at least three times in 24 hours, bleeding from the nose or gums, vomiting blood, blood in the stool. or feeling extremely tired or restless according to CDCSymptoms of severe dengue usually appear within 24 to 48 hours after the fever ends.
Across California, 250 cases of dengue were reported in 2023. Except for the cases in Pasadena and Long Beach, all were linked to out-of-state travel. This tally was the highest since then of 2019 Total 267.
At least 151 cases of dengue have been reported in California this year, including cases in Baldwin Park and Panorama City.
There are four dengue viruses that are related but distinct. Infection with one typically leads to lifelong immunity from that specific dengue virus, and short-term cross-protective immunity from others, Halai said.
But this also means that a person who has recovered from his first dengue infection can also get infected a second time. And a second infection increases the risk of serious illness, Halai said.
There is no antiviral medicine for dengue.
What increases the risk is that mosquito season typically starts earlier and ends later — potentially running from March to October, according to Farnad.
aedes aegypti, However, populations reach a peak slightly later than other mosquitoes, with maximum activity from August to October. The season ends when nighttime temperatures drop below 50 degrees, which is essentially too cold for them to breed.
“As nighttime temperatures consistently drop into the 40s or 50s, we see mosquito populations go down,” Farnad said. Mosquitoes still remain in winter, but the spread of disease and infestations generally go away.
aedes aegypti They prefer to live close to humans in cities, Farnd said.
“We find them mostly in backyards, growing in very small containers… from buckets, to flower pots, to old tires,” he said. “The more water is filled in these containers through sprinklers and other means, the more mosquitoes will breed. And the more leaves you have and the more shade you have, the more space these mosquitoes will have to rest and be comfortable.
Yards with sparse vegetation or drought-tolerant landscaping are less attractive.
Mosquitoes can breed in even a small amount of water stored in a bottle cap and take only five to seven days to develop from egg to adult, Farnad said.
According to Santa Clara County, mosquito eggs can survive for more than a year without water. aedes aegypti “Feeds almost exclusively on humans and does not fly long distances, flying less than 500 feet from where it emerges,” county officials said.
Northern California’s most populous county is targeted for devastation aedes aegypti When they are discovered. Efforts are underway to eradicate them in East San Jose and its neighborhoods Gilroy.
“If aedes aegypti Gaining a foothold in Santa Clara County would not only threaten public health, but also impact our quality of life, as these mosquitoes are highly aggressive and active during the day, unlike native mosquito populations, which are most active in the morning and evening. Are more active. When temperatures are cold,” Santa Clara County said in a statement,
residents may cause disturbance aedes aegypti By dumping standing water in their yard at least once a week, And throwing away any unused containers.
According to Santa Clara County, other sources of water that should be emptied regularly include pet dishes, fountains, bird baths, plant pots and saucers. Bird baths and scrubbing of pet dishes can also help remove dullness. aedes aegypti The eggs, which look like small pieces of clay and are about half a millimeter in size.
Officials say rain barrels should be properly screened or covered to prevent mosquito access, broken sprinkler heads should be fixed to avoid overwatering lawns, and ensure that To ensure that window and door screens do not have any holes or cracks.
using the mosquito repellent are also recommended – as long as they have EPA-approved active ingredients, such as DEETPicaridin, IR3535 or oil of lemon eucalyptus, Farnd said. Oil of lemon eucalyptus may also be listed by its chemical name, PMD.
The CDC says the use of EPA-registered insect repellents is safe and effective, including by pregnant and breastfeeding women. According to the CDC, oil of lemon eucalyptus should not be used on children under 3 years of age. They say,
According to , insect repellents are not meant to kill insects, but to prevent them from approaching humans by dulling their senses. National Pesticide Information CenterThe center said mosquitoes locate people to bite using the smell of our skin and the carbon dioxide we exhale, as well as heat, motion and visual cues.
People may also decide to treat their clothing, shoes, and camping gear with permethrin, an insecticide that kills or repels mosquitoes. CDC,
