The United States has recorded its first cases of domestically transmitted malaria for the first time in two decades. Dr. Debra Houry, the chief medical officer at the U.S. Centers for Disease Control and Prevention, said Tuesday the mosquito-borne disease was discovered in four people from Florida and one person in Texas.

Dr. Debra Houry: “So, it’s a concern because malaria is a life-threatening disease, it’s not often seen in the United States, and we hadn’t seen it domestically acquired in over 20 years.”

In 2021, malaria infected nearly a quarter-billion people worldwide, killing more than 600,000 of them. The disease is triggered by a parasite that’s spread to humans by certain types of mosquitoes that thrive in warm weather and humid conditions. In recent years, those mosquitoes have expanded their ranges in ways that are consistent with climate change.