Seymour Williams
Domestic Response Team Lead, Malaria Branch, Division of Parasitic Diseases and Malaria (DPDM), Centers for Disease Control and Prevention
Learn about the resurgence of locally transmitted malaria in the US in 2023. Find out about its history, causes and public health responses.
Malaria is a parasitic disease caused by the bite of an infective Anopheles mosquito. Approximately 2,000 cases of malaria are reported every year in the United States — almost all in people who have recently travelled internationally. However, 2023 marked the first time in 20 years that the US saw locally acquired mosquito-transmitted (LAMT) malaria cases.
US history of achieving malaria-free status
Malaria was introduced in what would become America in the 16th century and spread to the Southeastern and Southcentral regions of the country. Through effective insecticide spraying, swamp drainage and thorough case investigations and treatment, malaria control was eventually achieved and the US was certified as malaria-free in 1970. Over 156 sporadic local cases occurred in the US from the late 1950s to 2003. The 20-year period between 2003 and 2023 may be the longest malaria-free interval on record.
Travellers to malaria-endemic countries can
take important steps to protect themselves
when travelling to malaria-endemic areas.
Understanding the 2023 US cases
From May to October 2023, state health departments reported 10 cases of LAMT malaria to the Centers for Disease Control and Prevention (CDC). The cases occurred in Florida, Texas, Maryland and Arkansas, and all patients were treated and recovered. Though these cases were surprising, they were not unexpected.
Because of international travel to and from malaria-endemic areas, in addition to the sustained presence of mosquitoes able to transmit malaria in the US, LAMT malaria cases are still possible. Although the risk of LAMT malaria in the US remains very low, the 2023 cases highlight the importance of response.
Having a strong public health response allows for rapid detection, prompt treatment, enhanced surveillance and partnering with state and local health departments (SLHD). SLHDs led investigations with support from the CDC’s Division of Parasitic Diseases and Malaria to effectively address the outbreaks.
Global diseases require local vigilance
The 2023 LAMT malaria cases in the US spurred an important reminder that global diseases can be local ones, and it’s crucial to maintain vigilance. Travellers to malaria-endemic countries can take important steps to protect themselves when travelling to malaria-endemic areas through talking with their healthcare providers and taking medications to prevent malaria.
Healthcare providers should consider malaria as a potential diagnosis and test patients returning from malaria-endemic countries who have symptoms. For local cases, health department staff can investigate additional cases and decide on mosquito reduction actions in the surrounding areas.