You already know fall is a good time to get vaccinated against the flu and COVID-19. But these aren’t the only infectious diseases to be aware of in Southern California this season.
Los Angeles County Public Health officials, as of Oct. 24, are investigating five locally acquired cases of dengue, a mosquito-borne disease normally found in tropical climes.
“It’s extraordinarily unusual for there to be local transmission of dengue in Los Angeles County,” says Dan Uslan, MD, chief infection prevention officer for UCLA Health. “It’s unprecedented.”
Cases of Mpox are also on the rise in L.A. County. Then there’s bird flu, also known as highly pathogenic avian influenza, or HPAI, and West Nile virus – all these in addition to the most common illnesses of the season: flu and COVID-19.
“There’s never a dull moment in the field of infectious disease,” Dr. Uslan says.
Here’s what you need to know about these circulating viruses.
Dengue: Public health officials are looking into five cases of dengue in L.A. County: three in the Baldwin Park area, one in Panorama City and the most recent in El Monte. None of the infected people traveled to areas where dengue is endemic, which is what makes these cases unusual.
Dengue is a viral infection spread to people through mosquito bites. Symptoms include fever, headache, body aches, nausea and rash. These symptoms typically arise within two weeks of being bitten and last two to seven days.
The best way to prevent dengue infection is to avoid mosquito bites by using insect repellent, Dr. Uslan says. It’s also important to ensure there are no breeding areas for mosquitoes around your home, he adds.
Mosquitoes can breed in even small amounts of water, as little as a bottlecap full. Dr. Uslan advises surveying the area around your home – particularly in flowerpots, gutters and swimming pool covers – and eliminating any standing water.
To protect against mosquito bites, use insect repellent when spending time outdoors. The Environmental Protection Agency offers a tool to find the right repellent based on the bugs you need to protect against and any chemical allergies you may have.
When using both sunscreen and insect repellent, apply sunscreen first, Dr. Uslan says. Insect repellent creates “a cloud of vapor around your body,” he says, so it should be the last thing you put on before heading outside.
But don’t panic about dengue, he says.
“It's important to keep in mind that this is so far extraordinarily rare,” Dr. Uslan says. “There are only five cases in L.A. County out of the hundreds of thousands of mosquito bites residents have probably received this past summer, so I think people should be vigilant but not paranoid.”
West Nile virus: West Nile virus is also spread by mosquito bites. It’s more common than dengue and has similar symptoms, Dr. Uslan says.
“The symptoms of dengue and West Nile are so similar that L.A. County recommends essentially testing for both if someone comes in with symptoms,” he says. “The average clinician is not going to be able to distinguish between dengue and West Nile based solely on symptoms.”
He recommends seeking medical attention if you have mosquito bites and develop symptoms such as fever, muscle and joint pain, headache and rash.
Mpox: Previously known as monkeypox, mpox is a viral disease spread mainly through skin-to-skin contact or contact with contaminated items used by people with the virus.
L.A. County Public Health officials say cases of mpox more than doubled in September over the previous month. Case transmission is “significantly higher” in 2024 than 2023, officials say.
There are two types of mpox, called clades, Dr. Uslan explains. Clade I is associated with a higher percentage of people developing severe illness, he says. All the cases observed in L.A. County and across the country have been clade II. There have been no reported cases of clade I mpox in the United States, according to the U.S. Centers for Disease Control and Prevention.
Learn more about mpox, how it's transmitted and how it's treated
Sex workers, people who engage in group sex, and men and transgender people who have sex with men or transgender people are at highest risk for contracting mpox, health officials say. Symptoms – a painful rash with bumps or blisters, fever, body aches and swollen lymph nodes – typically emerge five to 21 days after exposure.
The best way to prevent transmission is to get vaccinated against mpox. A two-dose vaccine called JYNNEOS protects against infection and severe illness.
An antiviral medication called tecovirimat is being studied as a treatment for mpox, Dr. Uslan says. UCLA Health is conducting a clinical trial using this medication and can provide it to certain individuals, he says.
Highly pathogenic avian influenza (HPAI)/bird flu: The California Department of Food and Agriculture announced on Sept. 19 that HPAI was detected in a turkey flock in Merced County. Previously, the organization confirmed infections in cows at three Central Valley dairy farms.
On Oct. 4, 2024, the CDC confirmed two human cases of HPAI in California dairy workers. People most at risk of transmission are those in agricultural areas who have regular contact with birds and cattle.
“The risk in Southern California, particularly in Los Angeles, is extremely low, because we don’t have a lot of individuals who have exposure to those types of animals,” Dr. Uslan says.
People who consume unpasteurized or raw milk products should be concerned about HPAI, however, as the virus has been detected in unpasteurized milk from infected cows.
“We would recommend that they only ingest pasteurized dairy,” Dr. Uslan says.
Consuming meat from an infected animal presents no risk, so long as the meat is cooked, he says.
Flu and COVID-19: Even with these viruses in the mix this season, COVID-19 and influenza remain the most common, so be sure you’re up to date on your vaccines, Dr. Uslan says: “That would be more concerning than these other organisms.”
