There are four serotypes of dengue virus (DENV-1, DENV-2, DENV-3, DENV-4), which humans catch after they are bitten by an infected Aedes aegypti mosquito (or sometimes, Aedes albopictus). This has historically tended to occur in tropical and sub-tropical climates around the world, and usually in urban and semi-urban areas. After infection with one serotype, individuals are only immune to that serotype. But infection with another serotype can lead to an increased risk of severe dengue through a phenomenon known as antibody dependent enhancement. This presents serous challenges for the use of a dengue vaccine.
Although dengue infections are often asymptomatic or mild, severe dengue is still a risk. The severe cases can lead to lethargy, vomiting, pain, and later on, shock, bleeding, or organ damage. There is no treatment for dengue, and symptoms have to be managed carefully so that serious complications don't happen.
The US Centers for Disease Control and Prevention (CDC) is warning that dengue is now a risk in the United States. There has been a significant increase in the number of dengue cases in the past five years around the world, but most increases have happened in the Americas. Puerto Rico and the US Virgin Islands experienced outbreaks in 2024, and there was also confirmed, local dengue transmission in 2024 in California, Florida, and Texas. Already in 2025, there have been local dengue cases in Florida.
According to the CDC, in the Americas there were 4.6 million dengue cases and 2,400 deaths due to dengue in 2023, while there were around 13 million cases and 8,200 deaths in 2024. By March 6, 2025, there has been over 760,000 dengue cases in 2025, representing a 15% increase during the same time period compared to the 5-year average.
The World Health Organization (WHO) was already highlighting the increasing numbers of dengue worldwide in 2024.
And other health organizations are warning about the rising risk of the disease, such as the European Centre for Disease Prevention and Control. They note that over 1.4 million dengue cases and more than 400 dengue-related deaths have been confirmed in 53 countries around of the world as of March 2025.
New research reported in the Lancet Planetary Health has suggested that dengue may soon be endemic in the Americas.
This study also suggested that chikungunya may also be endemic in the Americas soon as well. Chikungunya, which is also currently causing an outbreak on the islands of La Reunion and Mayotte, is another viral disease that is transmitted by mosquitoes.
Chikungunya can lead to fever and severe joint pain, which may become chronic. There are also nonspecific symptoms like fatigue, headache, nausea, and rash.
There are no treatments for the illness. There are vaccines for the infection, but they are not yet widely available. Data on these vaccines is still being reviewed, and experts have not yet issues recommendations about their use.
Sources: CDC, WHO, Lancet Planetary Health
