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INTRODUCTION
The phylum Apicomplexa comprises a heterogeneous group of intracellular parasites, including species infectious for vertebrate and invertebrate organisms (Tenter et al. 2002). Some members of Apicomplexa are relevant for humans due to their economic or public health impact, such as Plasmodium spp., the causative agent of malaria; Toxoplasma gondii, which causes toxoplasmosis; Cystoisospora belli, causing isosporiasis; and Cryptosporidium, responsible for cryptosporidiosis. Also, livestock business, mainly poultry and cattle, have to cope with severe losses by disease impact and prevention costs for Eimeria infections.
Like all eukaryotic cells, these protozoa are provided with a nucleus, endoplasmic reticulum, Golgi complex and mitochondrion (Joiner and Roos, 2002). Interestingly, most apicomplexans possess a single, ramified mitochondrion. They also possess some peculiar and exclusive structures, like the apical complex, formed by cytoskeletal components (conoid and apical rings) and secretory organelles (micronemes and rhoptries) that are essential for invasion of the host cell (Morrissette and Sibley, 2002; Dubremetz, 2007; Carruthers and Tomley, 2008). Other characteristic secretory organelles of Apicomplexa are the dense granules, which modify the parasitophorous vacuole surrounding the intracellular stages of these parasites (Cesbron-Delauw et al. 2008). In addition to the above features, apicomplexans also contain a unique organelle, the apicoplast. Though the presence of this organelle has been well documented for decades by electron microscopy studies, only in the late 1990s the same structure was identified as an essential organelle derived from a secondary endosymbiotic event (Köhler et al. 1997). The apicoplast is a non-photosynthetic plastid essential for the Apicomplexa Type II fatty acid synthesis, isoprenoid biosynthesis and carbohydrate metabolism (Gleeson, 2000; Mazumbar et al. 2006; Fleige et al. 2007; Yeh and DeRisi, 2011). Interestingly, some Apicomplexa like Theileria and Cryptosporidium display further peculiarities: Theileria seems to lack fatty-acid biosynthesis enzymes, while Cryptosporidium appears to have lost the apicoplast during its evolution (Goodman and McFadden, 2007).
Some members of the Apicomplexa feature singular cytoplasmic inclusions sharing the same morphology but named with different terms, (Table 1) like the refractile body (RB) in Eimeria (de Venevelles et al. 2006) and Lankesterella (Desser, 1993); and the crystalloid body (CB) in Cystoisospora and Plasmodium (Garnham et al. 1969; Meis and Ponnudurai, 1987; Gleeson, 2000; Keithly et al. 2005). In addition...