At a glance
In 2023, CDC quickly developed a new genetic sequencing tool to identify the origins of several malaria cases reported across multiple states and to test whether the parasites from cases were related. The testing helped to confirm the first locally acquired cases of malaria in the United States in 20 years. Genetic sequencing is a tool that can be used to guide targeted public health responses and prevention efforts in communities for malaria.
Background
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.
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.
An unusual surge in cases
In 2023, CDC received reports of 10 cases of locally acquired malaria in four states, with nine cases caused by P. vivax among people with no travel history in Florida, Texas, and Arkansas.
Texas
1 P. vivax case
Maryland
1 P. falciparum case
1 P. vivax case
Within months of identifying these cases, CDC experts quickly developed a new genetic sequencing tool to determine the origins of the parasites.
Investigation and findings
CDC sought to understand if the nine P. vivax 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 P. vivax 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 outbreaks were the result of at least three separate introductions of malaria in the United States. The genetic testing also revealed the parasite strains were likely from Central or South America.
The testing confirmed that these were the first locally acquired cases identified in the United States in 20 years.
Public health implications
These cases serve as a reminder that the United States remains at risk for malaria outbreaks from local transmission. The mosquitoes capable of spreading malaria are common across the country. It is important for people to take steps to reduce their risk of mosquito bites to prevent malaria as well as several other mosquito-borne pathogens.
The genetic sequencing technology used to identify the origins of these cases can help public health officials determine where malaria strains come from, how local transmission develops, and who is at risk. This technology also informs the development of targeted prevention and treatment strategies for individuals and communities at risk.