[A case of Plasmodium ovale malaria--morphological diagnostic difficulty and utility of rapid diagnostic tests]

A 46-year-old Japanese man was referred to our travel clinic because of high fever for the past 7 days. He worked as an engineer for a month in Zambia and returned to Japan 2 days ago. He had a high-grade fever of 40.5 degrees C. Examination of the palpebral conjunctiva showed no evidence of anemia. Liver and spleen were not palpable. Blood sample was collected at the time of the febrile paroxysm. Malaria parasites were detected by examination of Giemsa-stained thin blood films. The dominant feature of parasite was early trophozoit with a low parasitemia (0.0469%, 1,857.6/microL). The James' stippling was absent. Schizonts and gametocytes were scarce. As ring morphology was quite variable, identification of species might not be possible. Identification of species is more difficult than usual, on the grounds that: 1) the blood sample contains rare early trophozoites, 2) the level of parasitemia is low, and 3) it is quite possible for parasites to be transformed due to the inappropriate treatment. Finally, the diagnosis was confirmed by nested PCR. Examination of Giemsa-stained blood films is the "gold standard" for detection and identification of organisms. However, in non-endemic countries, trained laboratory personnel are scarce and the most may be inexperienced in malaria diagnosis. It is recommended that personnel continue to gain experience by participating in external quality assurance schemes, and that routine laboratories utilize rapid diagnostic tests (RDTs) concurrently. The availability of simple and accurate RDTs could aid the diagnosis in no-endemic countries.