At a glance
In 2023, the CDC reported nine locally acquired malaria cases in Florida, Texas, and Arkansas, marking the first in 20 years. Genetic testing indicated multiple introductions, likely from Central and South America. This information can guide targeted public health responses and prevention efforts in communities.
An Unusual Surge
In 2023, CDC received reports of nine cases of locally acquired malaria in Florida (7), Texas (1), and Arkansas (1)—representing the first locally acquired cases identified in the United States in 20 years. Within months of identifying these malaria cases, CDC experts quickly developed a new genetic sequencing tool to determine where these parasites may have originated from. Genetic testing of the malaria-causing parasites revealed that all the Florida cases were related, but the Texas and Arkansas cases were not, suggesting the outbreak was the result of at least three separate introductions of malaria in the United States.
Background
The United States eliminated malaria in the early 1950s. In a typical year, the United States reports about 2,000 cases of malaria. Most of these cases are in people who contract malaria through a mosquito bite while traveling to another country and return to the United States. However, in 2023, CDC received reports of nine cases of malaria among individuals with no travel history—seven in Florida, one in Texas, and one in Arkansas. CDC assisted in confirming the malaria diagnosis through the agency's Diagnostic Parasitology Laboratory. These were the first locally acquired cases identified in the United States in 20 years.
Malaria is a disease caused by a species of parasite called Plasmodium. Female Anopheles mosquitoes carrying these parasites can transmit malaria to a person through a bite. Plasmodium vivax is one of four main types of malaria parasites that can infect humans. Symptoms often include fever, chills, and flu-like illness, and if not treated, the infection can be deadly
Investigation and Findings
CDC sought to understand if the 2023 cases were related and if they originated from a single case of malaria or multiple cases. To achieve this, CDC scientists used advanced genetic analysis techniques to identify where geographically the Plasmodium strain originated from and if the strains were closely related. CDC learned that the seven malaria cases in Florida were closely related. The single case in Texas and single case in Arkansas were unique from each other and from the cases in Florida. This suggests the outbreak in 2023 was the result of at least three separate introductions of malaria in the United States. Finally, the genetic testing revealed the parasite strains were likely from Central or South America. This information is helpful to guide malaria prevention efforts.
Public Health Implications
This study is a reminder that the United States remains at risk for malaria outbreaks from local transmission. The mosquitos capable of spreading malaria are common across the country. There are roughly 2,000 cases of imported malaria every year in the United States. People are exposed to and bitten by mosquitoes often. Knowing where malaria strains come from and how local transmission of cases develop helps public health officials understand who is at risk and why. They can develop targeted prevention strategies for at risk individuals and communities and ensure effective treatments are available.