First documented case of Plasmodium knowlesi infection in Denmark in a traveller returning from Malaysian Borneo

Abstract Plasmodium knowlesi has been reported as an emerging infection throughout the Southeast Asian region, especially in the Malaysian state of Sabah, where it accounts for the majority of the malaria cases reported. We present a case of P. knowlesi infection in a Danish woman returning from a short trip to Malaysian Borneo. The patient spent 14 days in forested areas of Sabah and fell ill after returning to Denmark in November 2022. Microscopy of blood smears revealed 0.8% infected erythrocytes, but due to the atypical morphological presentation, a conclusive species identification was made by molecular methods. The patient was treated successfully with artemisinin-based combination therapy. Plasmodium knowlesi is a potentially fatal infection, and taking the increasing travel activity into consideration after the coronavirus disease 2019 (COVID-19) pandemic, P. knowlesi should be a differential diagnosis in patients with travel-associated illness returning from highly endemic Southeast Asian areas.