Californians Confront Dengue and West Nile Virus Outbreaks

The State of California has reported an unexpected increase in diseases spread by mosquitoes, such as West Nile virus and Dengue.

Unfortunately, neither disease has a preventive vaccine available in 2024.

The California Department of Public Health (CDPH) confirmed on October 1, 2024, that Californians should take precautions against these mosquito-borne diseases.

This announcement follows six deaths caused by West Nile virus and ongoing transmission in many regions of California, particularly in the Central Valley. 

This year, CDPH has recorded 63 human cases of West Nile virus, including six deaths.

In Los Angeles County, the Department of Public Health has also reported four cases of locally acquired Dengue. Despite not traveling outside the country, these people became ill with Dengue in August and September 2024.

These are the first documented cases of locally acquired Dengue in California this year; two locally acquired Dengue cases were identified in Los Angeles County residents in 2023.

In some California counties, cases of Chikungunya virus have been reported. Five travel-associated infections have been confirmed this year.

Unlike the other diseases, Valneva SE's IXCHIQ® is an approved Chikungunya vaccine available in the U.S.

"It's important to remember that mosquitoes are still active well into cooler months," CDPH Director and State Public Health Officer Dr. Tomás Aragón said in a press release. 

Physicians concerned about West Nile virus treatment can find more information on the physician resource page on the West Nile virus website. 

California healthcare providers should have increased suspicion of Dengue among patients with fever who have been in areas with known dengue transmission or if they live in areas with invasive mosquitoes known to carry viruses.

If infection with Dengue is suspected in a patient, appropriate testing should be ordered. Clinical testing guidance and a case management guide for Dengue are available from the U.S. Centers for Disease Control and Prevention (CDC).

The CDC's June 2024 health alert has more information on the increased risk of dengue virus infections in the United States due to increased Dengue infections globally. 

As of October 2, 2024, the World Health Organization has classified Dengue as a grade 3 emergency, requiring a major to maximal response by public health.

Furthermore, this year, the CDC has issued extensive Travel Health Advisories regarding Dengue outbreaks.