Malaria Resurfaces in the U.S. for First Time in 20 Years
On August 28, 2023, the Centers for Disease Control and Prevention (CDC) issued an updated Health Alert Network (HAN) notice confirming new locally acquired cases of malaria in Florida, Texas, and Maryland. These cases add to the earlier reports from June and July, marking a rare and concerning return of mosquito-borne malaria transmission within the continental United States, a phenomenon not seen in over two decades.
In total, eight locally acquired malaria cases have now been confirmed: seven in Florida, one in Texas, and one in Maryland. These infections were not linked to international travel—a key distinction from the thousands of U.S. malaria cases reported annually, which are typically imported.
Public Health Response and Medical Guidance
The CDC emphasized the need for increased clinical awareness, mosquito control measures, and community education in the affected regions to minimize the risk of further transmission. In the updated alert, the CDC advised:
- Healthcare providers to consider malaria in patients presenting with fever, chills, sweating, headache, nausea, or vomiting, particularly if they live in or have traveled to areas where local transmission has occurred.
- Immediate diagnostic testing using rapid diagnostic tests (RDTs) or blood smears for suspected cases, with prompt initiation of treatment to prevent severe illness or complications.
- State and local health departments to enhance mosquito surveillance and control programs, and to issue public advisories regarding personal protection strategies such as using insect repellent, wearing long sleeves, and eliminating standing water.
While the risk to the general public remains low, public health officials warn that localized outbreaks could escalate without vigilant surveillance and swift public health intervention.
About Malaria and Transmission Risk
Malaria is caused by Plasmodium parasites, transmitted to humans through the bite of infected Anopheles mosquitoes. The most common species in the U.S. outbreaks has been Plasmodium vivax, known for causing relapsing infections, though it is generally considered less severe than Plasmodium falciparum.
While the U.S. eliminated endemic malaria in the 1950s, cases can still occur under favorable conditions, such as:
- Imported infections in returning travelers or migrants acting as reservoirs for transmission.
- The presence of competent mosquito vectors, particularly in warm and humid environments.
- Delays in diagnosis and treatment, allowing mosquitoes to pick up and transmit the parasite from infected individuals.
Local and National Coordination
In response to the 2023 cluster of cases, local health departments in Florida (particularly Sarasota and Manatee Counties), Cameron County in Texas, and Prince George’s County in Maryland have launched robust public health campaigns that include:
- Vector control efforts: Targeted spraying, larvicide application, and monitoring of mosquito breeding grounds.
- Public information outreach: Advisories on using insect repellent, repairing window screens, and seeking medical care for unexplained fevers.
- Coordination with the CDC and state epidemiologists to track and contain cases while expanding laboratory testing capacity.
The CDC continues to monitor nationwide mosquito surveillance systems and work closely with regional health departments to determine if additional cases emerge.
A Reminder of Global Disease Risks in a Changing Climate
Health experts caution that climate change, global travel, and urbanization are altering disease patterns, potentially increasing the frequency of rare infectious disease events in areas not traditionally affected. Rising temperatures and changing precipitation patterns create more favorable environments for mosquito breeding and longevity, raising concern about the reemergence of diseases once considered eradicated in the U.S.
While the recent cases do not suggest widespread transmission, they highlight the importance of sustained investment in public health infrastructure, vector control, and infectious disease preparedness.
CDC Recommendations and Resources
The CDC has provided updated clinical guidance, including treatment protocols and laboratory diagnostic tools, and continues to recommend:
- Clinician awareness for early detection.
- Enhanced community engagement on mosquito control practices.
- Robust disease reporting to local and state public health authorities.
Ongoing surveillance, rapid response, and public education will be essential in preventing further spread and protecting communities, especially in warm-weather states where mosquito activity remains high through the fall.
Source:
CDC Health Alert Network – Locally Acquired Malaria Cases in the U.S. (August 2023)
