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What is dengue fever? What to know as Puerto Rico declares epidemic due to virus spike

Health experts warn of surge in Dengue Fever
Health experts warning of Dengue Fever surge in tropical climates 03:57

Puerto Rico has declared a dengue fever epidemic following a spike in cases, prompting questions about the mosquito-borne virus.

The U.S. territory declared the public health emergency Monday, according to the Associated Press, noting at least 549 reported cases so far this year, compared with a total of 1,293 cases for all of last year.

More than 340 people have been hospitalized for the illness, according to the island's health department. The majority of cases have been reported in the capital of San Juan.

Almost half of the world's population live in areas with dengue risk, according to the Centers for Disease Control and Prevention. The virus is often a leading cause of illness in these areas, primarily in tropical and sub-tropical climates around the world.

"Each year, up to 400 million people are infected by a dengue virus," the CDC's website says. "Approximately 100 million people get sick from infection, and 40,000 die from severe dengue."

Health experts recently warned of the virus surging in tropical climates, including in North and South America. 

"Dengue often comes in cycles in regions where it occurs such as Mexico, the Caribbean, Central America and South America. This is a pretty bad year, especially in countries like in Brazil, where higher temperatures and rainfall have increased numbers of mosquitos," Dr. Albert Ko, a professor at the Yale School of Public Health, told CBS News in February. "The virus has been already circulating at high levels last year in the rest of South America, and increased travel and movement of infected people, especially coming out of the pandemic, has really contributed to the spread throughout the continents."

Last year, multiple cases of the virus were confirmed in Florida, according to the Florida Department of Health.

While the dengue virus typically comes from places outside of Florida, one of the cases reported in Miami-Dade was locally acquired, CBS Miami reports. 

Here's what to know about the virus: 

What is dengue fever?

Dengue virus, often referred to as dengue fever or "break-bone fever," due to pain being one of the major symptoms, is spread to humans through the bite of an infected mosquito.

Many people don't develop any symptoms, while others get a relatively mild case the of illness that typically gets better in 1 to 2 weeks, according to the World Health Organization. For some, however, the infection can evolve to severe dengue, which is a medical emergency that may require hospital care. 

Dengue symptoms

About 1 in 4 people infected with dengue will get sick, the CDC says, with symptoms ranging from mild to extreme. About 1 in 20 people who get sick will develop severe dengue, which can result in shock, internal bleeding and even death.

The most common symptom? Fever, which is usually accompanied by the following:

  • Nausea and vomiting
  • Rash
  • Aches and pains, including pain behind the eyes

If symptoms occur, they usually start 4 to 10 days after infection and last for 2 to 7 days, according to the WHO.

Additional warning signs that could point to severe dengue include: 

  • Belly pain, tenderness
  • Vomiting (at least 3 times in 24 hours)
  • Bleeding from the nose or gums
  • Vomiting blood, or blood in the stool
  • Feeling tired, restless or irritable

"Immediately go to a local clinic or emergency room" if you or a family member has any of those symptoms, the CDC says. "Warning signs usually begin in the 24 to 48 hours after your fever has gone away."

Dengue treatment

There is no a specific medicine to treat dengue fever. Most cases can be treated at home with pain medicine like acetaminophen to manage symptoms, the WHO says.

There is a vaccine called Dengvaxia for some people who have previously had dengue and live in a high-risk area.

Dengvaxia is the "only dengue vaccine approved by the U.S. Food and Drug Administration and recommended for routine use by the Advisory Committee on Immunization Practices," the CDC notes. It became available in 2022 for children and adolescents ages 9 to 16 in "dengue-endemic areas" which include American Samoa, Puerto Rico, and the U.S. Virgin Islands.

The best way to avoid getting dengue, however, is through preventing mosquito bites.

To prevent bites, experts advise using insect repellent and wearing loose-fitting, long-sleeved shirts and pants. The CDC and WHO recommend insect repellents with active ingredients that include:

  • DEET
  • IR3535
  • Oil of lemon eucalyptus (OLE)
  • Picaridin (KBR 3023)

CBS Miami notes some repellents are not suitable for young children: DEET is not recommended for children younger than 2 months old, while lemon eucalyptus oil should not be used on children under 3 years old.

Experts also advise clearing out standing water around your home or yard where mosquitoes might lay their eggs.

-The Associated Press contributed to this report.

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