Malaria, Here and Back Again

Column Author and Editor: Chris Day, MD | Pediatric Infectious Diseases; Director, Transplant Infectious Disease Services; Medical Director, Travel Medicine; Assistant Professor of Pediatrics, University of Missouri-Kansas City School of Medicine; Clinical Assistant Professor of Pediatrics, University of Kansas School of Medicine

Many readers will have seen the report of locally acquired malaria in Florida and Texas earlier this year. So far, a total of nine cases have been identified: seven in Florida (all in Sarasota County), one in Texas (Cameron County), and one more recent case in the National Capital Region of Maryland. All cases except the one in Maryland (Plasmodium falciparum) were Plasmodium vivax infection. Prior to this year, the last documentation of malaria acquired in the United States was in 2003, also in Florida, where eight cases of Plasmodium vivax infection were identified.  

Malaria can be transmitted to humans only by female mosquitoes belonging to genus Anopheles. Anopheles quadrimaculatus mosquitoes are widely distributed over the eastern half of the United States, from Florida to Maine and almost as far west as Colorado, and are competent vectors for the Plasmodium spp. parasites that cause malaria. The risk of malaria transmission rises with travel from endemic countries and when the local climate allows for mosquito vectors to survive throughout most or all of the year.^1,2

Malaria was once endemic in many parts of the United States. Anecdotes and statistics from some of the country’s wars illustrate the impact malaria had prior to elimination in the United States. Cornwallis left the Carolinas for Yorktown at least in part to escape the havoc that mosquito-borne diseases, including malaria, were causing among his troops. After Cornwallis’s defeat, Nathanael Greene’s troops threatened to desert rather than endure another disease season in malarious South Carolina while awaiting a formal peace. Later, in 1850, the Census Bureau estimated 45.7 of every 1,000 deaths in the U.S. were from malarial fevers. In the Civil War, 1.3 million U.S. Army recruits were recorded as having contracted malaria and 10,000 of them are estimated to have died from the disease.^3,4

Mosquitoes were first clearly identified as a malaria vector in 1897 by Ronald Ross, a British army officer in India. In part by targeting mosquitoes, efforts to reduce the incidence of malaria and yellow fever during the building of the Panama Canal and the U.S. military occupation of Cuba had some success. The United States Public Health Service (USPHS) was granted funding by Congress in 1914 for early federal efforts to control malaria domestically (see Figure 1). In 1942, malaria threatened war efforts at military bases in the South. The Office of Malaria Control in War Areas (MCWA), established to reduce this threat, trained state and local health officials in malaria control. The direct successor to MCWA was the Communicable Disease Center of the U.S. Public Health Service (CDC), now the Centers for Disease Control and Prevention, which was founded in Atlanta because most malaria transmission was in the South. The National Malaria Eradication Program, with participation by the CDC, began operations on July 1, 1947. By 1951, malaria was considered eliminated in the U.S.⁵

Malaria should always be considered potentially life-threatening. Travelers returning from endemic regions who have fevers without a clear source should be evaluated. Residents of, and even visitors to, areas where sporadic locally acquired cases have occurred may also need evaluation, though risk, even in Florida, remains very low. Symptoms of malaria are nonspecific (commonly fever with chills, sweats, headache, muscle pain, nausea and vomiting). Illness typically manifests after an incubation period of seven to 30 days, but malaria needs to be considered in patients who have been in endemic areas during the past year. Malaria is usually diagnosed by thick and thin blood smears that are specifically stained to identify intraerythrocytic parasites. Multiple blood smears (the CDC recommends three) are needed before malaria can be excluded. A malaria diagnosis should be established by laboratory testing prior to initiating therapy; however, once the diagnosis is made, immediate treatment is recommended. The CDC has published an algorithm describing these steps.⁶ 

When malaria is diagnosed in a child at Children’s Mercy Kansas City, infectious diseases providers will recommend hospitalization. We will often need to confer with the CDC Malaria Hotline about therapy. The choice of antimalarial for treatment will vary based on the Plasmodium sp., the region of acquisition (due to differences in susceptibility between regions), and the severity of illness. Severe malaria, defined as any case with one or more clinical criteria (impaired consciousness/convulsions/coma, severe anemia [hemoglobin < 7 mg/dL], acute kidney injury, acute respiratory distress syndrome, circulatory shock, disseminated vascular coagulation, acidosis, jaundice, plus at least one other sign) and/or parasite density ≥ 5%   should be treated with IV artesunate, if available. A combination drug (artemether-lumefantrine) with another artemisinin derivative is first line for most non-severe malaria infections that have the potential to be chloroquine resistant. Extensive treatment guidance is provided in yet another CDC document.⁷ Always reach out to your local infectious diseases provider with any malaria case.

Figure 1. Malaria Morbidity and Mortality Rates in All States Reporting Cases and Deaths During 1920-1946 Inclusive. 

References:

1. Center for Preparedness and Response. Locally acquired malaria cases identified in the United States. Centers for Disease Control and Prevention. Last reviewed June 26, 2023. https://emergency.cdc.gov/han/2023/han00494.asp
2. Rios LM, Connelly RC. Anopheles quadrimaculatus. University of Florida Entomology and Nematology Department. Latest revision August 2015. https://entnemdept.ufl.edu/creatures/aquatic/Anopheles_quadrimaculatus.htm#:~:text=Anopheles%20quadrimaculatus%20mosquitoes%20are%20primarily,%2C%20Carpenter%20and%20LaCasse%201955
3. McCandless P. Revolutionary fever: disease and war in the Lower South, 1776-1783. Trans Am Clin Climatol Assoc. 2007;118:225-249. PMID: 18528506. PMCID: PMC1863584.
4. Hong SC. The burden of early exposure to malaria in the United States, 1850-1860: malnutrition and immune disorders. J Econ Hist. 2007;67(4):1001-1035. PMID: 19081796. PMCID: PMC2600412. doi:10.1017/S0022050707000472
5. Global Health, Division of Parasitic Diseases and Malaria. Elimination of malaria in the United States (1947 — 1951). Centers for Disease Control and Prevention. Last reviewed July 23, 2018. https://www.cdc.gov/malaria/about/history/elimination_us.html
6. Global Health, Division of Parasitic Diseases and Malaria. Malaria diagnosis (United States). Centers for Disease Control and Prevention. Last reviewed July 23, 2018. https://www.cdc.gov/malaria/diagnosis_treatment/diagnosis.html
7. Global Health, Division of Parasitic Diseases and Malaria. Treatment of malaria: guidelines for clinicians (United States). Centers for Disease Control and Prevention. Last reviewed June 28, 2023. https://www.cdc.gov/malaria/diagnosis_treatment/clinicians1.html