Largest dengue outbreak in Florida in decades

Florida is currently experiencing what is probably the largest dengue outbreak in several decades on the US mainland. According to the US health authority CDC, almost 250 locally transmitted cases have already been reported in the state this year. This refers to infections that are not related to travel. In addition, there is a roughly equal number of infections among returning travelers.

According to US media reports, Hillsborough County is particularly affected. The administrative region on the west coast of the state, whose capital is Tampa, declared a state of emergency at the end of September due to the high number of cases. At the beginning of the month, an elderly woman infected with the dengue virus died in Florida, according to the AP news agency.

Dengue fever is an infectious disease that is transmitted by a specific type of mosquito: the Aedes aegypti, also known as the yellow fever mosquito, dengue mosquito or Egyptian tiger mosquito. According to the Robert Koch Institute (RKI), three out of four people affected show no or only mild symptoms.

However, a very small proportion of those affected experience a severe course, which can become apparent three to seven days after the first symptoms appear. In these cases, there are, among other things, severe abdominal pain, persistent vomiting, rapid breathing, bleeding mucous membranes, exhaustion and, in the worst case, symptoms of shock. Severe cases of an initial infection are very rare. In the case of second infections, however, the risk of this is significantly increased.

Dengue mosquitoes are spreading

For a long time, the tropical pathogen was found in the USA primarily in people returning from international travel. According to experts, this is changing because the dengue mosquito is spreading more widely.

“The effects of climate change with temperature increases, more frequent heat waves and flooding events are leading to this,” writes the RKI. Vectors - i.e. living beings that transmit pathogens from an infected host to another organism without becoming ill themselves - could also adapt to new environmental conditions outside of the known tropical and subtropical endemic areas. The dengue virus has continued to spread geographically in recent years. “Illnesses are now also occurring sporadically in previously non-endemic countries.”

There are now many Aedes aegypti mosquitoes, particularly in southern Florida, says Michael Johansson, epidemiologist at Northeastern University, in a report in the US magazine “TIME”. In his opinion, there is a simple reason why dengue fever has not spread more widely: many people in Florida stayed in air-conditioned rooms during the day. The mosquitoes are primarily active during the day.

In addition to Florida, other US states have also been affected by higher numbers of cases in the past, such as Hawaii. On the mainland, however, according to U.S. health officials, there haven't been this many people who have been infected locally - rather than while traveling - within a calendar year since the 1940s. This is suggested by the available information, although data for dengue outbreaks are limited.

How do you protect yourself from dengue when traveling?

The number of dengue cases imported into Germany in 2025 and the first half of 2026 was lower than in previous years, as the RKI reports. Travelers from Germany became infected most often in South and Southeast Asia as well as in South and Central America.

In order to protect yourself from infection, consistent mosquito protection of the whole body is required. Health experts advise: not only use mosquito spray on the skin, but also impregnate long-sleeved clothing with it.

According to the RKI, the Asian tiger mosquito (Aedes albopictus), which is a potential vector for chikungunya, dengue and Zika viruses, is spreading in parts of Germany. In addition, the West Nile virus (WNV), transmitted by domestic mosquitoes (Culex), has been circulating for several years.