To Break a Fever: Relapse of Long-Latency <i>Plasmodium vivax</i> Malaria After Service in the Korean Peninsula

Plasmodium vivax malaria is a threat to armed forces operating in the Korean Peninsula. Surges in malaria cases in the Republic of Korea entail increased risk. We report 6 cases from a cluster of P. vivax malaria cases in a non-endemic setting in active duty personnel who had redeployed from the Korean Peninsula. Demographics, disease course, and laboratory data were collected on 6 patients diagnosed with Plasmodium vivax malaria at Fort Bliss in 2022. All patients were males, with a mean age of 23 years (range 20-27 years), exposed in the Dagmar North training area in the Gyeonggi province in 2021, with an average time from symptom onset to diagnosis of 57 days (8-121 days). All had uncomplicated malaria. Laboratory findings included hemoglobin of 12.1g/dL (range 8.1-14.2 g/dL), platelets of 123 × 103/µL (range 40-171 × 103/µL), and parasitemia <1% (0.1%-0.9%) with diagnosis on peripheral smear and/or rapid antigen testing. No cases received chemoprophylaxis. Patients were treated with artemether/lumefantrine and primaquine. Clearance of parasitemia on peripheral smear was seen after an average of 2.8 days (range 2-4 days). Changing vector ecology and increased tempo of training exercises in the Dagmar North Region near the Demilitarized Zone are hypothesized to contribute to this cluster of cases. Malaria diagnosis post-deployment in non-endemic regions is challenging due to the long latency of illness onset and requires clinician vigilance. Preventive measures of pre-deployment should also be emphasized.