According to the Pan American Health Organization (PAHO), Latin America is currently experiencing its worst dengue fever outbreak on record. The number of cases reported in the first 4 ½ months of 2024 has already surpassed last year's record of 4.1 million cases by 238%. This year's cases are also over 400% higher than the five-year average.

The outbreak has been attributed to an unusually wet and warm summer season caused by the El Niño weather pattern. These conditions have created ideal breeding grounds for the Aedes aegypti mosquitoes, which spread dengue, allowing them to hatch in large numbers and carry higher amounts of the virus.

Experts warn that this outbreak may be a glimpse into future dengue fever trends, as climate change continues to create favorable conditions for the spread of mosquito-borne diseases. Dr. Albert Ko, a professor of epidemiology at the Yale School of Public Health, expresses concern about the potential impact on regions like North America and Europe, where dengue hasn't been prevalent in recent history.

Dengue fever, caused by four different viruses and transmitted through mosquito bites, has traditionally been common in tropical regions. However, the range of the Aedes aegypti mosquitoes is expanding, with sightings reported as far north as the Bay Area and Washington, D.C. A 2019 study predicts that by 2080, an additional 2 billion people will be at risk for dengue fever.

Dr. Gabriela Paz-Bailey, dengue branch chief at the Centers for Disease Control and Prevention (CDC), explains that dengue outbreaks historically occurred in the Americas every three to four years but are now happening annually due to climate change. Rising temperatures allow the mosquitoes to breed year-round and replicate the viruses at a faster rate, increasing the chances of infection. In South America, dengue cases have appeared earlier in the season than usual.

While locally transmitted dengue infections are still rare in the continental U.S., there have been isolated cases reported in select states, such as California, Arizona, Florida, and Texas. Last year, Europe experienced local transmission in countries like France, Italy, and Spain during record-breaking heatwaves.

The threat of dengue fever becoming more common worries health experts like Paz-Bailey, who emphasizes the need to address the significant increase in cases where the virus is already endemic. Although significant dengue outbreaks are not expected on the U.S. mainland this summer, there is a possibility of imported cases as people travel to regions with higher-than-usual incidence rates.

The challenge lies in containing the disease, as humans serve as reservoirs for dengue. Once enough people become infected, the mosquitoes can reliably spread the virus. Puerto Rico serves as an example of this tipping point, with a significant outbreak fueled by ongoing transmission between humans and mosquitoes.

Florida, for instance, has reported 176 dengue cases this year, with the majority being in individuals infected in other countries, mainly Brazil and Cuba. Only seven cases of locally transmitted dengue have been recorded so far in 2024, compared to 173 cases in 2023, mainly in Miami-Dade County.

The symptoms of dengue fever include fever, headaches, fatigue, nausea, vomiting, rash, and severe body aches. Most people recover within a week or two, but about 1 in 20 develop severe dengue, which can be life-threatening. The risk of severe symptoms increases with each subsequent infection.

While the U.S. does have a dengue vaccine, it is currently approved only for children aged 9 to 16 who reside in endemic areas such as Puerto Rico, American Samoa, or the U.S. Virgin Islands. Moreover, the vaccine is only administered to children who have previously had a dengue infection due to the risk of severe illness if vaccinated prior to a first infection.

As dengue fever continues to challenge public health, experts stress the importance of vigilance, mosquito control measures, and further research to mitigate the impact of climate change on the proliferation of mosquito-borne diseases.