The spillover of zoonotic diseases, such as SARS-CoV-2, mpox, and yellow fever, continues to make headlines globally, and now, malaria has joined this list with a notable resurgence in the U.S. On June 26, 2023, the Centers for Disease Control and Prevention (CDC) issued a Health Alert Network notification regarding locally acquired malaria in Florida and Texas—the first such cases in the U.S. in two decades. While the overall risk of locally acquired malaria remains low, the presence of Anopheles mosquito vectors across many regions of the country necessitates vigilance. These mosquitoes can transmit malaria if they bite an infected person. Additionally, the CDC is working to ensure access to IV artesunate, a critical treatment for severe malaria cases.
Current Malaria Cases in the U.S.
On June 23, 2023, the Texas Department of State Health Services (DSHS) reported a case of locally acquired malaria in a Texas resident with a history of working outdoors but no travel history outside the state or country. DSHS is collaborating with local health departments to investigate potential additional exposures, though no other locally acquired cases have been identified in Texas so far.
In Florida, as of July 19, 2023, there have been seven locally acquired cases of Plasmodium vivax (P. vivax) malaria. Investigations have shown no evidence linking the cases in Florida with the single case in Texas. All patients received prompt treatment at local hospitals and are currently recovering. In response, the Florida Department of Health has issued a statewide advisory for mosquito-borne illnesses. Both Texas and Florida are urging residents to take precautions to prevent mosquito bites.
Laboratory Detection and Diagnosis of Malaria
In the U.S., malaria diagnoses are typically associated with travelers returning from malaria-endemic regions. Given its rarity, clinicians may not be familiar with malaria, potentially leading to delays in diagnostic testing and treatment. Additionally, laboratory personnel may lack experience with malaria detection, which can lead to missed diagnoses.
Diagnosis is challenging as malaria symptoms—such as fever, chills, sweat, headaches, muscle pains, nausea, and vomiting—overlap with those of other diseases. Therefore, confirmatory laboratory testing is crucial for timely treatment and to prevent further transmission.
The gold standard for malaria detection remains the blood smear. This involves spreading a drop of the patient’s blood on a microscope slide, staining it, and examining it microscopically to identify malaria parasites in various stages—ring forms, schizonts, trophozoites, and gametocytes.
Rapid Diagnostic Tests (RDTs) offer a practical alternative to microscopy, especially when it is unavailable. These immunologic tests detect malaria antigens using a dipstick or cassette format, providing results in 2–15 minutes. While RDTs are useful, they must be validated for accuracy.
Molecular tests using PCR (Polymerase Chain Reaction) are highly sensitive and specific. These tests can identify malaria species but may not always provide rapid results necessary for immediate treatment.
Serological tests can detect antibodies against malaria parasites, though they are typically used for epidemiological studies rather than for diagnosing current infections. Advances in diagnostic technology, including flow cytometry and nucleic acid amplification tests (e.g., PCR and loop-mediated isothermal amplification), offer new tools for detecting malaria and other infectious diseases.
Moreover, glucose-6-phosphate dehydrogenase (G6PD) testing is essential, particularly for individuals with G6PD deficiency, as primaquine treatment for P. vivax can cause hemolysis in these patients. Recent advancements in point-of-care G6PD testing provide a valuable tool for managing malaria treatment effectively.
In addition to the common diagnostic tests, physicians should conduct a complete blood count and routine chemistry panel to assess the severity of the malaria infection and identify any complications, such as severe anemia, hypoglycemia, renal failure, hyperbilirubinemia, and acid-base disturbances.
Implications for Public Health
The increased risk of locally acquired and imported malaria, along with other infectious diseases, is partly driven by climate change. Factors such as higher temperatures, heat waves, rainfall, and floods create favorable conditions for mosquito populations. Enhanced surveillance and sustainable mosquito control methods are vital public health strategies to address the risk of malaria and other vector-borne diseases.
Rodney E. Rohde, PhD, MS, SM(ASCP)CM, SVCM, MBCM, FACSc
Regents’ Professor, University Distinguished Professor, Honorary Professor of International Studies, Global Fellow, and Chair in the CLS Program at the College of Health Professions; Associate Director, Translational Health Research Center at Texas State University; Associate Adjunct Professor of Biology at Austin Community College
Email: rrohde@txstate.edu