When Prior Exposure Doesn't Protect: Imported Plasmodium falciparum Malaria in a Returning Traveler With Waning Immunity.

Malaria remains a leading cause of infectious morbidity worldwide, yet imported cases present a diagnostic challenge in non-endemic settings. We report a case of imported malaria in a previously healthy 35-year-old man, who presented with increasing fatigue, jaundice, and cyclical fevers following travel to an endemic area. Peripheral blood smear demonstrated Plasmodium falciparum trophozoites, prompting initiation of antimalarial therapy. Further testing detected previously undiagnosed glucose-6-phosphate dehydrogenase (G6PD) deficiency. The patient improved clinically and was discharged after five days of hospitalization. This case illustrates two important considerations in the management of imported malaria. First, Visiting Friends and Relatives (VFR) travelers, those who grew up in malaria-endemic areas and now reside in other countries, represent the highest-risk group for imported malaria. Nonetheless, this population is among the least likely to use chemoprophylaxis - a pattern driven by a misconception of residual immunity shared by both patients and clinicians. As a result, this misconception can delay diagnosis: the patient's presumed immunity contributed to an initial misattribution of symptoms to a viral illness, highlighting the need for a low threshold to test for malaria in febrile returning travelers. Second, this case underscores the importance of G6PD testing before initiating antimalarial regimens, as many first-line medications carry the risk of oxidative hemolysis in patients with G6PD deficiency. Recognition of these issues is imperative for safe and effective management of malaria in non-endemic settings.