The life cycle of a typical Theileria species, as illustrated by those of T. annulata and T. parva, comprises a cycle of clonal replication of schizonts in mononuclear cells in lymphoid and reticuloendothelial tissues followed by the appearance of 'piroplasms' - small (<3u) and plemorphic organisms - in erythrocytes.  T.parva  proliferates as schizonts; its piroplasms do not multiply.  Schizonts are the major proliferating stage of T. annulata..  In infections of T. annulata, at least, elevated parasitaemias arise when erythrocytes are invaded by massive numbers of merozoites produced by large populations of schizonts. Members of the  T. orientalis/T. buffeli  group proliferates mainly as piroplasms. In every species, piroplasms include parasites undergoing gametogony and producing the gametocytes which are infective for ticks. Differentiation into gametes and sexual recombination occurs in the tick gut. Kinetes developing from zygotes in the gut cells appear to migrate directly to the
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