A dengue fever alert has been issued in the Florida Keys following two confirmed cases of the mosquito-borne illness.

The local warning comes a week after the Centers for Disease Control and Prevention issued a national advisory about the increased risk of dengue virus infections in the United States.

Even though most of the dengue cases reported in the states so far this year have been travel-related, the two cases that triggered the alert in the Florida Keys were locally acquired, according to officials at the Florida Department of Health in Monroe County.

A total of 2,241 dengue cases have been reported so far this year in the U.S., including 1,498 cases in the U.S. territory of Puerto Rico, where a public health emergency was declared in March after cases exceeded historical figures.

The CDC reported 3,036 dengue cases last year in the U.S. and its territories.

The incidence of dengue fever internationally has been the highest on record, especially in Latin American countries, where more than 9.7 million dengue cases have been reported so far this year. That’s twice as many as in all of 2023 (4.6 million cases), according to the CDC.

Dengue infections are on the rise as many nations have reported increasingly hot temperatures, which create ideal conditions for the mosquitoes that spread dengue to hatch en masse and carry higher amounts of the virus.

About one in four people who get infected with the dengue virus will get sick, according to the CDC. Among those who get sick, the symptoms can be mild or severe.

The most common symptom among those who contract the mosquito-borne disease is fever along with other symptoms such as joint, muscle, bone or eye pain, headache, nausea, vomiting or rash.

Most dengue patients recover in a week, but about 1 in 20 cases will develop severe dengue, which can be life-threatening and require hospitalization since it can result in shock, internal bleeding and even death.

Those who have had dengue in the past are more likely to develop severe symptoms. A person can get sick with dengue fever up to four times in their lifetime — once for each type of virus that can cause the disease, according to the CDC.

Some prevention methods include staying in places with air conditioning when possible or installing window screens to keep mosquitoes out of the home, using insect repellent when outdoors or wearing long sleeves and pants to avoid mosquito bites and cleaning up any areas with stagnant water where mosquitoes could breed such as buckets and roof gutters, among other containers.