Prevention against mosquito bite in tropical destinations.

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In 2023, sporadic cases of locally acquired mosquito-transmitted malaria were reported in various US states. A concerning trend of rising imported malaria cases highlights the ongoing risk posed by malaria to travelers returning to the US from endemic regions, as well as potential challenges in controlling sporadic local transmissions.

During January–December 2023, a total of 68 imported malaria cases were identified across 3 public health jurisdictions along the US southern border like Pima, Arizona, San Diego, California, and El Paso, Texas. This marked an increase from 28 cases in 2022. Enhanced case investigations were initiated due to higher-than-expected case counts. Among the 68 cases in 2023, 15 occurred among US residents, 2 among newly arrived refugees, 49 among other newly arrived migrants, and 2 among travelers with unknown immigration status.¹

Among the total 68 cases, 15 (22%) were among U.S. residents, 2 (3%) among newly arrived refugees, and 49 (72%) among other new arrivals. Patient interviews were attempted in 61 (90%) cases, and case investigations were completed in the same number. However, only 33 (49%) cases were included in local surveillance data. Most cases involved complex travel patterns, with 46 (68%) patients having transited through one or more countries with endemic malaria. Plasmodium vivax accounted for 34 (50%) cases, followed by Plasmodium falciparum with 21 (31%) cases. Most patients (62; 91%) were hospitalized, with 21 (31%) experiencing severe malaria. No deaths were reported, and 18 (27%) patients were available for follow-up after treatment.¹

The increase in imported malaria cases in 2023, particularly among new arrivals with recent travel through malaria-endemic countries, highlights the importance of comprehensive travel history assessment and prompt testing and treatment. Consistent investigation and reporting protocols for non-US residents could improve the characterization of malaria incidence among different subgroups.

Travelers and Malaria in the US

Travelers to malaria-endemic regions face varied risks, necessitating personalized prevention strategies. Despite the approximately 2000 annual US cases of travelers’ malaria, local transmission remains rare, thanks to environmental conditions and mosquito behaviors.

Malaria in the US is primarily associated with travelers’ malaria. This includes people visiting from malaria-endemic countries or US residents who travel to countries with ongoing transmission. Upon their return, they may already be infected, bringing the parasites back with them and starting to show symptoms, according to Prakash Srinivasan, PhD.” “So that’s what is called travelers malaria. And usually, there are about 2000 cases of travelers malaria every year in the US. But this year after almost 2 decades, of no local transmission of malaria.” ²

To mitigate malaria morbidity, outreach and education efforts targeting healthcare professionals and new arrivals must be intensified. Continued vigilance and proactive measures are essential to reduce the risk of malaria transmission and ensure the well-being of travelers in the US.

References

1. Mitchell C, Kennar A, Vasquez Y, et. al. Notes from the Field: Increases in Imported Malaria Cases — Three Southern U.S. Border Jurisdictions, 2023. Morbidity and Mortality Weekly Report (MMWR). Published May 9, 2024. Accessed May 17, 2024. https://www.cdc.gov/mmwr/volumes/73/wr/mm7318a2.htm?s_cid=mm7318a2_e&ACSTrackingID=USCDC_921-DM127971&ACSTrackingLabel=This%20Week%20in%20MMWR%3A%20Vol.%2073%2C%20May%209%2C%202024&deliveryName=USCDC_921-DM127971

2. Navigating Malaria Control. Contagion. Published February 22, 2024. Accessed May 17, 2024. https://www.contagionlive.com/view/navigating-malaria-control