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Home » Dengue fever hits Southern California – there’s a vaccine for that

Dengue fever hits Southern California – there’s a vaccine for that

Although I have focused on common diseases, like COVID-19, flu, measles, and such, that doesn’t mean that there aren’t other dangerous diseases that should cause worry. On 20 October 2023, the Pasadena (California) Public Health Department reported a case of dengue fever in a Pasadena resident who did not travel elsewhere.

This is the first confirmed case of dengue fever in California that was not associated with travel to another location. This case is interesting because dengue is not endemic in California.

This post will examine dengue fever and this case found in Pasadena.

black white mosquito
Photo by Pixabay on

What is this Dengue fever?

Dengue fever is one of four viruses transmitted by the Aedes aegypti mosquitoes to humans. It infects over 100 million people a year worldwide. A. aegypti is endemic to areas around Los Angeles, along with Pasadena.

The principal symptoms of dengue fever are high fever, severe headache, severe pain behind the eyes, joint pain, muscle and bone pain, rash, and mild bleeding (e.g., nose or gums bleed, easy bruising). Generally, younger children and those with their first dengue infection have a milder illness than older children and adults. 

Dengue hemorrhagic fever (DHF) is a more severe form of dengue infection. It can be fatal if unrecognized and not properly treated in a timely manner. DHF is caused by infection with the same viruses that cause dengue fever. With good medical management, mortality due to DHF is still significant but can be reduced to less than 1%.

Dengue fever is not transmitted from one person to another with direct contact, only from the bite of the A. aegypti mosquito.

Although Dengue fever is rare in the USA, there have been outbreaks in 2009 and 2010 in the Florida Keys, and one in 2005 in Texas. There are several outbreaks of dengue fever observed across the world in 2023. And with higher temperatures and sea level rises, the mosquito vectors for Dengue will move further and further north putting more of the world population at risk.

Florida has been trying to eradicate the dengue-carrying mosquitos by using genetically modified mosquitos to breed with the native population of mosquitos. The initial studies have shown a lot of promise, and without any foreknowledge on my part, they could be used in the Los Angeles area if more dengue fever cases appear.

There is a vaccine to prevent dengue. It is approved for children ages 9 – 16 who have previously had dengue and live in areas where dengue is common. Clearly, your local Los Angeles-based pediatrician is not going to have the vaccine available. And it probably won’t become widely available in Southern California unless there are many more cases of dengue.

One of the best ways to prevent dengue is by avoiding mosquito bites:

  • Wear insect repellent with DEET or another U.S. Environmental Protection Agency (EPA)-registered insect repellent. Make sure to follow the instructions for using the repellant.
  • Wear clothes that cover your arms, legs, and feet.
  • Close unscreened doors and windows.

Dengue fever in California

The San Gabriel Valley Mosquito and Vector Control District has deployed traps to assess the mosquito population. As of today, testing has not identified any dengue-infected mosquitos.

According to Dr. Matthew Feaster, Pasadena Public Health Department Epidemiologist:

PPHD has been conducting surveillance and investigation of mosquito-borne diseases in Pasadena for years.

Our work so far, in partnership with the Vector Control District, gives us confidence that this was likely an isolated incident and that there is a very low risk of additional dengue exposure in Pasadena.


Although dengue fever is a serious infectious disease, it’s hard to read into any concerns about this one case. It is surprising that dengue fever was acquired locally in Pasadena, as it is not endemic to California.

Furthermore, the local health departments and mosquito abatement districts jumped into action to determine if the disease suddenly showed up in the area. Early data shows that it has not, but it warrants continued monitoring.

I can only hope that this one case is it, and dengue fever has not migrated to California from other areas of the world. But as of this moment, it does not appear that we should worry. Plus, we have a vaccine for that!

Michael Simpson

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