Florida's dengue outbreak is now the largest in the continental US in decades

Florida is dealing with its worst dengue outbreak in a very long time. So far this year, more than 250 people in the state have caught dengue from local mosquitoes — meaning they did not have to travel anywhere to get sick. Most of those cases are in Hillsborough County, which is home to the city of Tampa. Health experts say this is the biggest dengue outbreak in any U.S. state since at least the 1940s.

Officials in Hillsborough County and nearby counties have declared local emergencies. Workers are spraying day and night in the Tampa area to kill the mosquitoes that spread the disease. They are also checking properties for pools of standing water, because that is where mosquitoes like to lay their eggs. One person — an elderly woman from Tampa — has died from dengue this year.

Dengue (say it like "DEHN-gay") is a disease caused by a virus that mosquitoes carry. Many people who get infected never feel sick, but others develop a fever and flu-like symptoms. One of the most well-known signs is extreme body pain, which is so bad that dengue is sometimes called "breakbone fever." In serious cases, dengue can cause bleeding, shock, and even death.

There are four types of dengue virus, called types 1, 2, 3, and 4. When a person gets infected with one type, their body makes antibodies that protect them from that type for life. However, if they later get a different type of dengue, those old antibodies may not protect them — and can actually make the new infection worse. This tricky problem has made it hard for scientists to create a vaccine that works well against all four types.

Dengue spreads through the bites of certain mosquitoes that live in warm places. For a long time, most dengue cases in the continental United States came from people who caught the virus while traveling to other countries. But in 2009 and 2010, Key West, Florida, saw the first local dengue cases in the continental U.S. since 1945. The biggest U.S. outbreak before this one happened in Hawaii, where 264 people got sick over six months in 2015 and 2016.

Scientists say dengue-carrying mosquitoes are spreading to more parts of the United States because of climate change. Warmer temperatures allow these mosquitoes to survive in places they could not live before. Around the world this year, more than 2.2 million dengue infections and nearly 1,200 deaths have been reported. In the U.S., there have been nearly 1,900 local cases this year, mostly in Puerto Rico.

Experts are not entirely sure why Tampa has been hit so hard this year. Florida gets a lot of visitors from Puerto Rico and other places where dengue is common, and some of those travelers may have brought the virus with them. Usually, most of Florida's dengue cases are in the southern part of the state near Miami, not the Tampa area. Dawn Wesson, a dengue expert at Tulane University, says travel patterns may be playing a big role in this year's unusual surge.

There are steps that people can take to avoid getting dengue. Using insect repellents that contain DEET or other approved ingredients can help keep mosquitoes away. People should also wear loose, long-sleeved shirts and long pants to protect their skin. Staying indoors, especially behind window screens or in air-conditioned rooms, will also lower the chance of being bitten.

People can also help stop mosquitoes from breeding by getting rid of any standing water on their property. Things like old tires, flowerpot saucers, and buckets can collect rainwater and become places where mosquitoes lay eggs. Getting rid of that standing water is one of the best ways communities can slow the spread of dengue. Wesson warns that outbreaks like this one may become more common in the future, saying, "There's a good chance that this is the new normal."