Los Angeles Malaria Outbreak Arrived From the South

Since the start of 2023, the U.S. Centers for Disease Control and Prevention (CDC) has received ten reports of Plasmodium vivax malaria cases treated in Los Angeles, California.

This uptick in LA was not forecasted, as only 2 cases of P. vivax were reported from 2016 to 2022.

The CDC revealed on May 6, 2024, that these individuals had probably traveled from Panama's Darién Gap through Central America and Mexico before arriving in LA.

The CDC's Research Letter, Volume 30, Number 7—July 2024, stated these individuals met the criteria for uncomplicated malaria and were treated with either hydroxychloroquine, chloroquine, or atovaquone/proguanil, followed by anti-relapse treatment with primaquine.

In response to this finding, the CDC now recommends that all patients in LA be screened for malaria when they have compatible symptoms and that a detailed travel history be obtained.

A vital detail to consider with travel history is that patients with prior P. vivax infection can relapse weeks, months, or years after initial diagnosis because the parasites can lay dormant in the liver as hypnozoites. According to the CDC, this latent stage poses a potential risk for transmission to another human through an infected mosquito.

In conclusion, clinical microbiology laboratories, particularly those in border states, should consider implementing rapid antigen testing for malaria to improve turnaround time for case detection.

However, Dr. Paloma Khamly, with the Los Angeles General Medical Center, wrote that physicians should be aware of the potential for false-negative results in patients with low parasitemia levels.

Malaria remains a leading cause of preventable illness and death in the world.

In the United States, 1,503 travel-related malaria cases were reported in 2021.

In 2024, states such as Florida and Texas have reported malaria cases. 

In Florida, twenty cases of malaria with onset in 2024 have been reported in individuals with a travel history to a malaria-endemic area.

In 2023, 78 travel-related malaria cases and seven locally acquired malaria cases were reported in Florida.

In Texas, the Department of State Health Services's Amira Bashadi, MPH, reported on February 16, 2024, that from 2013 to 2022, 1,239 casalaria cases were reported in Texas.

In 2022, there were 166 malaria cases in Texas.

Of these, 98% were acquired from international travelers from Africa, Asia, and South America.

While malaria is a vaccine-preventable disease, neither of the two approved malaria vaccines is offered in the U.S. as of May 8, 2024. However, the CDC says international travelers can protect themselves from malaria by taking prescription medicine and preventing mosquito bites.

Update: On May 9, 2024, the U.S. CDC Notes From The Field published during 2023, a total of 68 imported malaria cases were identified in Pima, Arizona (18), San Diego, California (27), and El Paso, Texas (23), compared with 28 cases in 2022.