Genetically modified mosquitoes and vaccines -- what to know about dengue fever

More than 3 million cases of dengue fever have been reported in the Americas this year with over 882 in the United States, according to the CDC. This is the second highest annual rate in the Americas since 1980.

Dengue is spread through mosquitoes, which thrive at hotter temperatures and humid conditions. These conditions have become more frequent in the past few years as a result of record heat and extreme weather, which results in more cases of dengue, according to Nature.

Experts say the rise in cases are a "canary in a coal mine" for what is to come as we see changes in rainfall and temperature patterns.

The cases in the U.S. have increased from 814 in 2021 to 2,261 in 2022, and over 50% of these cases have been locally acquired in the United States. The disease has been circulating in California, Florida, Texas and New York, but cases in the U.S. have been growing over the past few years, and are expected to rise with climate change and urbanization.

"This is concerning," says Dr. Krutika Kuppalli, infectious disease physician and chair of the Infectious Disease Society of the Americas Global Health.

The growing number of cases are a signal that public health officials in the U.S. and around the world need to invest more resources into tracking and protecting against dengue, Kuppalli says. Officials have not been tracking as much as they should because resources were allocated to COVID-19 management, she says.

"A lot of people think that the United States is impervious to mosquito-borne illness," says Dr. Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security. "That's just not true," he added.

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If it seems like mosquitoes are on the attack in Southern California - perhaps more so this year than in years past - that's because they are.

Here is what you need to know about dengue fever including what it is, signs, symptoms, treatment, and how to prevent it.

What is dengue fever?

Dengue fever is a virus spread to people through Aedes mosquitos. These mosquitoes also spread Zika, chikungunya, and other viruses. A person can be infected with dengue multiple times in their life, according to the CDC.

What are the symptoms?

Most people infected with dengue will have mild or no symptoms. If symptoms occur, they usually appear between 4-10 days after a mosquito bite and last for 2-7 days, according to the World Health Organization. People typically get better in 1-2 weeks. Symptoms include headache, high fever, muscle and joint pain, nausea, vomiting, swollen glands and rash.

Mild symptoms can be confused with other illnesses that can cause fever, aches, pains and/or rash. In rare cases, dengue can be severe. "People do not realize that it can cause serious infection or lead to death," Kuppalli says.

Severe dengue is a medical emergency and can get worse rapidly. Those who have had an infection before are more likely to develop a severe infection. People with severe dengue may have severe abdominal pain, rapid breathing, increased thirst, blood in vomit or stool, pale and cold skin, persistent vomiting, blood in gums or nose and weakness.

Those who have severe symptoms should seek medical attention right away.

What is the treatment?

There are no antiviral treatments for dengue, Adalja says.

People are treated with fluids and medications that can control pain and bring down a fever, like acetaminophen. The CDC and WHO recommend avoiding aspirin and ibuprofen, which can increase the risk of bleeding.

Is there a vaccine?

A dengue vaccine is approved for use in children between ages 9-16 with previous laboratory-confirmed dengue infection. They must also be living in areas where dengue occurs frequently or continuously. That includes some areas like the U.S. territories of American Samoa, Puerto Rico and U.S. Virgin Islands.

"It's really beneficial in those individuals who have had one type of dengue before," says Dr. Adalja. The vaccine is not approved for Americans who are simply traveling to areas with high levels of dengue.

How do we prevent it?

If you are traveling or living in an area with dengue, the best way to prevent infection is by preventing mosquito bites, according to the CDC. Steps you can take include, wearing protective clothing, applying insect repellent with DEET, Picaridin or IR3535, using mosquito nets and using window screens.

Some regions take steps to control the mosquito population by removing places where mosquitoes lay eggs, killing eggs with larvicides and killing the adult population with adulticides. Others use methods include the use of genetically modified mosquitoes, which have been approved by the Environmental Protection Agency (EPA) for use in some counties in Texas and Florida.

These mosquitoes have a gene that prevents female mosquitoes from living to adulthood, so they can't continue to reproduce - which reduces the population. "Genetically modified mosquitoes are an important tool," Dr. Adalja says.

The EPA says that use of genetically modified mosquitoes poses no risk to people, animals or the environment.

Adiba Matin M.D. is a resident physician in emergency medicine at the Mayo Clinic and is a member of the ABC News Medical Unit.