Q&A: CDC issues warning amid surge in dengue virus
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Key takeaways:
- The CDC issued a health warning about an elevated number of cases of dengue in the U.S. this year.
- Suspected cases in the Americas are more than double what they were at this time last year.
In March, Puerto Rico declared a public health emergency after recording 549 cases of dengue virus since the start of 2024. The number rose to more than 1,900 cases as of July 24, according to the CDC.
In June, the CDC issued a health alert about an increased risk of dengue infection in the United States, noting that the global incidence of the mosquito-borne disease in 2024 is the highest on record at this point of the year.
According to the Pan American Health Organization, there have been more than 10.7 million suspected cases of dengue in the Americas this year as of July 25 — a 233% increase over the same time period in 2023 and a 419% increase over the average number of cases in the same time period from the last 5 years.
The CDC reported 2,869 cases in 48 U.S. jurisdictions as of July 24, nearly 2,000 of which were defined as locally acquired — most of them occurring in Puerto Rico.
Florida is the only U.S. state with any recorded local infections this year — 12 in total — but the CDC noted that there have been more travel-related cases in the U.S. than expected this year, totaling 920.
We spoke with Healio | Infectious Disease News Editorial Board Member Lyle Petersen, MD, MPH, director of the Division of Vector-Borne Diseases at the CDC, to learn more about the threat of dengue this summer.
Healio: Are Aedes aegypti mosquitoes spreading to new areas?
Lyle Petersen: The northern spread of Aedes aegypti in the western U.S. is particularly noteworthy. In recent years, the mosquito has spread into much of California, as well as into cities like Las Vegas and Phoenix.
Healio: How does climate change fit into this conversation?
Petersen: Many intersecting factors may explain the surge of dengue cases globally, including increased temperatures, human mobility, urbanization and viral evolution. These factors act synergistically. Thus, teasing out the relative importance of any one of these factors is extremely difficult, if not impossible.
Nevertheless, warmer temperatures increase viral replication in mosquitoes and shorten the time from when they take a blood meal to when they can transmit infection. This has a huge impact on the ability of vector mosquitoes to transmit dengue and other mosquito-borne viruses.
Healio: What explains the increasing number of locally acquired cases in Florida?
Petersen: More than 10 million dengue cases have been reported in the Americas so far this year, a figure more than twice that reported in all of 2023, which by itself was a record year. Thus, more travelers are encountering areas with intense dengue transmission and returning to the U.S. with dengue. After return, local Aedes aegypti mosquitoes that bite these persons can become infected and begin a local transmission cycle.
Healio: How are we testing for cases?
Petersen: Dengue testing is available at some commercial laboratories, state laboratories and at the CDC. We recommend that suspect cases are tested for the presence of dengue virus with either a nucleic acid amplification test or NS1 antigen test, and for the presence of IgM antibodies. Some commercial laboratories offer IgG antibody tests, which have no role in the diagnosis of clinical dengue.
Healio: Are we catching all of them?
Petersen: I suspect that we are catching a minority of patients with dengue because many persons with mild symptoms may not seek medical care or dengue may not be recognized clinically.
Healio: Sanofi said it will stop making the only dengue vaccine that has been approved for use in the U.S. because of a lack of demand. When will that vaccine supply run out, and do you anticipate that any other approved or candidate vaccines will be available in the U.S. any time soon?
Petersen: The Sanofi vaccine is recommended in the U.S only for children 9 to 16 years old, who live in dengue-endemic areas and who have laboratory-confirmed evidence of previous dengue infection. This has greatly reduced the number of persons eligible for the vaccine.
Furthermore, the need for pre-vaccination screening and a three-dose primary vaccination series over a year has proven logistically challenging and has greatly reduced vaccine uptake. Existing vaccine lots will expire in August 2026, so children must begin the vaccination series in mid-2025.
In July 2023, Takeda voluntarily withdrew its biologics license application for its vaccine candidate (TAK-003), so there is no timeline when it may become available in the U.S., if ever.
Merck and the Instituto Butantan are collaborating on the development of live-attenuated tetravalent dengue vaccines initially developed by the NIH, one of which (TV003/TV005) is currently being evaluated in a large phase 3 study in Brazil. The timeline when this vaccine will be available in the U.S. cannot yet be determined. However, availability is unlikely in the next several years.
Healio: What is the takeaway for clinicians, and anybody else, with the increase in dengue detection and cases in many parts of the U.S.?
Petersen: In light of the increased global and domestic incidence of dengue, clinicians should suspect dengue in febrile patients who have returned from an area where dengue transmission is endemic or ongoing within 14 days before clinical onset.
It is critical to order appropriate diagnostic tests. Reporting of dengue cases to public health authorities is also important so local control measures can be undertaken.
Promoting the use of Environmental Protection Agency-registered mosquito repellents by persons who live in or travel to dengue endemic areas should be a mainstay of dengue and other mosquito-borne disease prevention.
References:
- CDC. Dengue: Current year data (2024). https://www.cdc.gov/dengue/data-research/facts-stats/current-data.html. Updated July 24, 2024. Accessed July 29, 2024.
- CDC. Increased risk of dengue virus infections in the United States. https://emergency.cdc.gov/han/2024/han00511.asp. Published June 25, 2024. Accessed July 29, 2024.
- Situation report No 27 — dengue epidemiological situation in the region of the Americas — epidemiological week 27, 2024. https://www.paho.org/en/documents/situation-report-no-27-dengue-epidemiological-situation-region-americas-epidemiological. Updated July 25, 2024. Accessed July 29, 2024.
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