Figure 1. Plasmodium cynomolgi parasites (arrows) in Giemsa-stained thin smears of blood from a traveler returning from Southeast Asia to Denmark. Overall, few parasites were visible in the thin film, and no schizonts were visible at all. A) Young trophozoite. The cytoplasm is ring shaped, and the nucleus is spherical. The erythrocyte is not enlarged, and neither Schüffner’s dots nor pigment are visible. B) Growing trophozoite. The young parasite is ring shaped and takes up more than half of the diameter of the host erythrocyte. The cytoplasm has become slightly amoeboid. Schüffner’s dots are more prominent than in P. vivax at this stage. Pigment is visible as small yellowish granules in the cytoplasm. Erythrocyte enlargement is not evident. C) Growing trophozoite. The cytoplasm appears amoeboid but relatively compact. Schüffner’s dots are prominent, but no pigment is seen in the cytoplasm. The erythrocyte is slightly enlarged. D) Growing trophozoite. The cytoplasm appears amoeboid, and the nucleus has increased in size. Schüffner’s dots and yellowish pigment are prominent. Enlargement of the erythrocyte is evident. E) Growing trophozoite. The host cell is further enlarged. The cytoplasm is amoeboid as in P. vivax at this stage. Schüffner’s dots are clearly visible, and yellowish pigment is dispersed within the cytoplasm. F) Growing trophozoite. An infected erythrocyte with major alteration in the shape, similar to that sometimes seen in P. vivax–infected erythrocytes. The cytoplasm is amoeboid, with hardly any pigment. Schüffner’s dots are prominent, and the host erythrocyte is enlarged. G) Growing trophozoite. The cytoplasm is amoeboid and appears relatively compact. Schüffner’s dots are dominant. Pigment is visible in small granules but appears more yellowish-brown and is scattered around in the cytoplasm. H) Near-mature trophozoite. The parasite is becoming more compact with an enlarged nucleus. No ring or amoeboid form is visible. Schüffner’s dots are very dense, and abundant yellowish-brown pigment is clearly visible in the cytoplasm. I) Mature microgametocyte. It is round and resembles that of P. vivax at the same stage. The nucleus is diffuse and takes up most of the parasite. The stippling of the host cell is forced toward the periphery, as seen for P. vivax. Microgametocytes stain reddish-purple (pink hue) in contrast to macrogametocytes, which stain light blue. The yellowish-brown pigment is scattered around in the parasite. Scale bars indicate 100 μm.