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Malaria was eliminated in the United States in the mid-1950s, but about 2,000 cases a year are still imported by travelers from places where it spreads — about 200 of them in Maryland. Anopheles mosquitoes that can carry malaria live in many parts of the country, so imported cases are a possible source of local infection. No locally acquired (autochthonous) mosquito-borne cases had been found since 2003 — until mid-2023, when eight Plasmodium vivax cases turned up in Florida and Texas, each near an imported case.
Malaria cases in Maryland by month and year, January 2019–August 2023. Image from CDC's report
The Maryland case
| Date (2023) | |
|---|---|
| August 6 | a previously healthy resident of the Maryland National Capital Region is seen after 7 days of fever, malaise and muscle aches. No international travel, transfusions or injection drug use — but daily walks near home and a tick bite |
| tests show anemia, low platelets, high bilirubin and parasites inside red blood cells — babesiosis or malaria. Given the tick bite and no travel, doctors treat for presumed babesiosis | |
| August 9 | a blood smear is reported as Plasmodium falciparum malaria, with 3.2% of red cells infected; CDC's remote review of the images can't tell malaria from Babesia for certain |
| August 10 | parasites down to 0.2%; the patient goes home to finish 7 days of babesiosis treatment |
| August 15 | the Maryland Department of Health (MDH) laboratory identifies P. falciparum by smear, rapid test and PCR |
| August 18 | CDC confirms P. falciparum by PCR; the Babesia PCR is negative. After the babesiosis course, the patient is treated with artemether-lumefantrine |
Notably, one drug in the babesiosis regimen, atovaquone, is part of a malaria medicine, and doxycycline is used to prevent falciparum malaria.
The response
- Confirmed that household members were well and the patient hadn't traveled abroad.
- Issued a public notice urging residents to avoid mosquito bites and seek care for malaria symptoms, and alerted clinicians to prioritize timely diagnosis, treatment and reporting.
- Searched local hospitals for other cases: none within 5 miles (8 km) in the previous month.
- With the Maryland Department of Agriculture, trapped mosquitoes and applied several rounds of larvicide and adulticide. Anopheles mosquitoes were found near the home, but none of 21 tested carried P. falciparum.
The source of infection is still unknown, and no further locally acquired cases have been found in Maryland.
Lessons
- Malaria and babesiosis can look alike under the microscope.
- Sporadic local cases can happen in the United States.
- Travelers to malaria-endemic regions should take preventive medicine, protecting themselves and their communities.
- Labs need capacity for quick diagnosis: blood smears, rapid tests, PCR to confirm species — and clinicians should ask CDC for help early.
CDC's Malaria Hotline: 770-488-7788 or 855-856-4713 (toll-free), weekdays 9 a.m.–5 p.m. EST; after hours, 770-488-7100.
Sources
Based on Monique Duwell, Timothy DeVita, David Torpey and others, "Notes from the Field: Locally Acquired Mosquito-Transmitted (Autochthonous) Plasmodium falciparum Malaria — National Capital Region, Maryland, August 2023," MMWR, volume 72, Centers for Disease Control and Prevention; a work of the United States government in the public domain.
Licence : CC0 1.0 (domaine public) · Adapté de www.cdc.gov
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