Babesia are hematoprotozoa that infect erythrocytes and which need to be distinguished from Plasmodium species. Only trophozoite and merozoite stages are present, with the trophozoite resembling the ring form of P. falicparum.
Features of Babesia:
(1) trophozoites show more variation in size, ranging from 1 to 5 microns in diameter; the smallest trophozoites are smaller than those seen in malaria (around 2 microns)
(2) larger trophozoites have a clear vacuole
(3) extracellular forms may be present
(4) erythrocytes may contain 2 or 4 parasites after division; merozoites may occasionally be seen as tetrads forming a "Maltese cross"
Features of malaria that are absent:
(1) no parasite-associated pigment is present
(2) no schizonts or gametocytes are present
The number of organisms may be low, especially in early infections. Therefore multiple microscopic must be examined.
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