Imported Malaria Rose in Three U.S. Southern Border Jurisdictions in 2023

Malaria is a severe, potentially fatal disease caused by Plasmodium parasites and spread by mosquitoes. It is no longer endemic in the United States, but about 2,000 imported cases are reported each year, mostly in U.S. residents returning from places where malaria is common. In 2023 a handful of cases spread by local mosquitoes also turned up in several states.

This CDC field report looked at a rise in imported malaria in three public health jurisdictions on the U.S. southern border.

More cases than expected

Because the counts were higher than expected, the three health departments began enhanced case investigations, recording where each patient lived and how they had traveled. They sorted patients into U.S. residents and new arrivals — people born outside the United States who had arrived within the past 6 months — divided into refugees, other new arrivals (asylum seekers and other migrants), and people whose immigration status was unknown.

Who got sick

Of the 68 patients in 2023:

• 15 (22%) were U.S. residents
• 2 (3%) were newly arrived refugees
• 49 (72%) were other new arrivals
• 2 (3%) had unknown immigration status

The U.S. residents and refugees had flown directly from a country with endemic malaria. Among the 49 other new arrivals, 46 (94%) had passed through one or more countries with endemic malaria, including their country of origin — what the report calls complex travel. Their journeys lasted a median of 29 days (range 8–85), and 36 (73%) had crossed land borders. Travel began mostly in South America (27 patients) or Africa (29, including 14 of the U.S. residents).

Only 33 of the 68 patients (49%) were counted in local surveillance figures, because the jurisdictions had different rules for patients without a local address.

How sick they were

• 62 (91%) were hospitalized; no one died.
• 21 (31%) had severe malaria — 11 with P. vivax, 6 with P. falciparum and 4 with another or unknown species.
• Severe disease was more common among other new arrivals (18 of 49, 37%) than among U.S. residents (1 of 15, 7%).

What it means

The increase came mainly among new arrivals whose journeys took them through at least one country with endemic malaria. Over the same period, more asylum seekers and other migrants entered across the southern land border. The authors note that new arrivals with complex travel may be at higher risk of malaria and, for reasons not fully understood, of severe illness. Consistent investigation and reporting rules for non-residents would help health departments compare new-arrival groups across jurisdictions.

For clinicians: take a full travel history, consider malaria in anyone with symptoms after recent travel through an area where it is endemic, and test promptly — then treat if needed. Outreach to local health care workers and to new arrivals matters because quick care, diagnosis and treatment reduce illness.

Sources

Based on Mitchell CL, Kennar A, Vasquez Y, et al., "Notes from the Field: Increases in Imported Malaria Cases — Three Southern U.S. Border Jurisdictions, 2023," MMWR Vol. 73, No. 18, CDC; a work of the United States government in the public domain. The report’s text gives 63 hospitalized patients, but its table gives 62 (91%), which matches its other rows; the page uses the table’s figure.