Avian Flu Diary: California: LA County Announces 2nd & 3rd Locally Acquired Dengue Cases of 2024

Credit Wikipedia

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In 2009 Dengue fever returned to Florida after a nearly 60 year absence (see 2010 MMWR report Locally Acquired Dengue --- Key West, Florida, 2009--2010), likely brought in by a viremic tourist, who provided a blood meal to a local mosquito.

By the end of 2010 65 cases had been identified in Key West, although the CDC issued a report indicating far more people were exposed (see CDC Press Release Report Suggests Nearly 5 Percent Exposed to Dengue Virus in Key West).

So far in 2024 Florida's Department of health has detected more than 500 imported cases of dengue, although many others go undetected. Some spillover into local mosquitoes is inevitable - and thus far in 2024 - Florida has reported 35 cases of locally acquired dengue from seven counties.

Texas has reported scattered locally acquired cases as well, and last year - for the very first time - California reported 2 local cases (see CIDRAP California confirms 2nd local dengue case). Over 2015-2016, Hawaii saw a large outbreak with > 230 locally acquired cases.

Every state, however, sees imported cases, and so the risk of spillover remains high across much of the nation. Florida, Texas and Hawaii have borne the brunt of these mosquito-borne diseases in the past, but much of the country has the right environment - and the right kind of mosquitoes - to support limited outbreaks during the summer.

We've seen repeated warnings over the years that climate change, international travel, and the introduction of new mosquito vectors are all contributing to the global spread of these (formerly) tropical diseases, and over the past nine months we've seen an explosion of cases in South America.

WHO DON: Geographical Expansion of Dengue and CHKV in the Region of the Americas

PAHO Epidemiological Alert: Chikungunya In The Americas

Three months ago the CDC issued a warning (see HAN # 00511: Increased Risk of Dengue Virus Infections in the United States) that the risks of seeing more imported - and locally acquired - cases of Dengue in the United States was rising.

Ten days ago LA County announced their first locally acquired case of Dengue (see below).

September 09, 2024

Public Health Confirms Case of Locally Acquired Dengue
The Los Angeles County Department of Public Health has confirmed a case of locally acquired dengue in a resident in the City of Baldwin Park, who has no history of travel to areas where dengue is endemic. It is the third case of locally acquired dengue in California and the first reported by the Los Angeles County Department of Public Health. Cases of locally acquired dengue were previously confirmed by Long Beach and Pasadena in fall 2023. No additional suspected locally acquired cases have been identified at this time.
While the potential risk for widespread dengue virus transmission in Los Angeles County remains low, these cases highlight the presence of infected mosquitoes locally and underscore the importance of preventive measures to control the spread of this virus.
Dengue fever, transmitted primarily through the bite of infected Aedes mosquitoes, can cause flu-like symptoms including high fever, severe headache, pain behind the eyes, joint and muscle pain, rash, and mild bleeding. In severe cases, it may lead to dengue hemorrhagic fever or dengue shock syndrome, both of which require immediate medical attention.

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Fast forward 9 days, and yesterday LA County announced two more cases.

September 18, 2024

Public Health Investigating Unprecedented Cluster of Locally Acquired Dengue Cases - Residents urged to take steps to prevent ongoing transmission
The Los Angeles County Department of Public Health is investigating two additional cases of locally acquired dengue in residents of the City of Baldwin Park. These residents have no history of travel to areas where dengue is endemic prior to their symptoms. This now brings the total number of cases of locally acquired dengue in LA County in 2024 to three, which is an unprecedented number of locally transmitted cases for a region where dengue has not previously been transmitted by mosquitoes. Public Health initially reported a confirmed case of locally acquired dengue on September 9, 2024.
Dengue is primarily transmitted through the bite of an infected Aedes mosquito. Although Aedes mosquitoes are common in LA County, cases of locally acquired dengue are extremely rare. Almost all previously reported dengue cases in LA County have been associated with travel to a country where dengue is commonly spread.
These additional cases of local virus transmission are a stark reminder for all Los Angeles County residents that simple steps to prevent mosquito breeding and mosquito bites can lower the risk of mosquito-borne diseases and prevent more sustained transmission in the future.
Dengue fever can cause flu-like symptoms including high fever, severe headache, pain behind the eyes, joint and muscle pain, rash, and mild bleeding. Severe cases can result in shock, severe bleeding and severe organ impairment which require immediate medical attention.
Symptoms of dengue may mimic other viruses so healthcare providers should be vigilant for dengue fever in patients with acute febrile illness and test for and report suspect cases of mosquito-borne diseases. Providers should also routinely discuss mosquito bite prevention with patients and travelers.

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As we've discussed previously (see EID Journal: Hx of Mosquitoborne Diseases In the U.S. & Implications For The Future), at one time tropical diseases like Malaria and Yellow Fever were rife in the U.S., sparking epidemics as far north as New England.

Outbreaks of yellow fever reported during 1693–1905 among cities comprising part of present-day United States. - Credit EID Journal

Although the greater use of air conditioning, window screens, and mosquito control efforts certainly reduces the risks in the United States, since West Nile Virus arrived in North America 25 years ago millions of people have been infected (albeit, most asymptomatically) and several thousand have died.

Dengue and WNV aren't the only exotic mosquito borne diseases to threaten the United States, as we also see thousands of imported Zika, Chikungunya, and Malaria cases each year. And this summer, a new threat has emerged (see CDC HAN Advisory: Increased Oropouche Virus Activity and Associated Risk to Travelers).

While it might not be at the top of your list of stock up items for your Hurricane/Disaster kit, having (and using) mosquito repellent for you and your family is highly recommended.

For some earlier mosquito-borne illness blogs, you may wish to revisit: