Piroplasmia

Pi·ro·plas·mia (pi″ro-plaz-meґə) [L. pirum pear + plasma] a subclass of heteroxenous parasitic protozoa (class Sporozoea, subphylum Apicomplexa), occurring as piriform, round, or rod-shaped cells or ameboid cells without a conoid, oocysts, spores, pseudocysts, and flagella, and usually without subpellicular microtubules but with a polar ring and rhoptries. Locomotion is accomplished by flexion, by gliding, or, in sexual stages of certain species, by large axopodium-like organelles (strahlen). They are parasitic in the erythrocytes and other circulating and fixed cells of the host, with merogony occurring in vertebrates and sporogony in invertebrates, and producing sporozoites with a single-membraned wall. Ticks are the vectors of most of the piroplasmids. It comprises a single order: Piroplasmida.