Life cycle stages, specific organelles and invasion mechanisms ofEimeriaspecies

Abstract

Apicomplexans, including species of Eimeria, pose a real threat to the health and wellbeing of animals and humans. Eimeria parasites do not infect humans but cause an important economic impact on livestock, in particular on the poultry industry. Despite its high prevalence and financial costs, little is known about the cell biology of these ‘cosmopolitan’ parasites found all over the world. In this review, we discuss different aspects of the life cycle and stages of Eimeria species, focusing on cellular structures and organelles typical of the coccidian family as well as genus-specific features, complementing some ‘unknowns’ with what is described in the closely related coccidian Toxoplasma gondii.

The Growth of Eimeria tenella: Characterization and Application of Quantitative Methods to Assess Sporozoite Invasion and Endogenous Development in Cell Culture

“…Results correlated with previous findings for some of these proteins: (i) presence of alternative types of surface antigen proteins (SAGs) between sporozoites and merozoites (Tabares et al, 2004 ); (ii) high abundance of microneme (MIC) proteins during invasion (Bumstead and Tomley, 2000 ); and (iii) overexpression of rhoptry (ROP) and dense granule (GRA) proteins during endogenous development (Oakes et al, 2013 ; Xue et al, 2020 ). These data further corroborate the suitability of the in vitro system to mimic endogenous development (Burrell et al, 2020 ) and are an important source of information to design specific interventions for the study of these relevant proteins. The detection by MS of these proteins indicated that they are present at significantly abundant levels to be targeted (e.g., antibody binding, enzymatic cleavage) and evaluated by this in vitro system.…”

Do All Coccidia Follow the Same Trafficking Rules?

“…Nevertheless, the physical presence of dense granule organelles is elusive in Eimeria sporozoites [7]. Dense granules, as defined in T. gondii and other apicomplexans, have not been visualized by electron microscopy of sporozoites of E. tenella [7,91]. Along with a lack of visual evidence of dense granules, there is sparse conservation of genes encoding GRA protein orthologues in Eimeria genomes, as evidenced by the low numbers of T. gondii GRA orthologues found in transcriptomic [92], proteomic (in E. tenella) [93,94], and protein characterization studies [95], where less than 10 proteins have been identified as potential Eimeria GRAs in comparison to the 53 proteins annotated for T. gondii (www.toxodb.org, accessed on 26 August 2021).…”

“…This process is followed by sexual reproduction (gametogony) to form new oocysts. Then, these new oocysts are voided to the environment via the feces, where sporulation (sporogony) takes place [ 7 ]. Similarly, when ingested by felids (definitive host), Toxoplasma oocysts (or tissue cysts) release sporozoites (or bradyzoites) that, after the invasion of host cells, undergo asexual (endopolygeny) and sexual (gametogony) replication in the gut epithelium, producing oocysts that are released to the environment [ 8 ].…”

“…Nevertheless, the physical presence of dense granule organelles is elusive in Eimeria sporozoites [ 7 ]. Dense granules, as defined in T. gondii and other apicomplexans, have not been visualized by electron microscopy of sporozoites of E. tenella [ 7 , 91 ].…”

“…Recent studies have estimated that coccidiosis costs > £10 billion per annum to the global poultry sector [ 6 ], making coccidiosis a target for active research in academia and industry. Whereas work on T. gondii provides valuable insights into the mechanisms of coccidian invasion, differences in the specific infection biology between parasites, such as host-range, tissue- and site-specificity, PV formation, the mechanism of asexual cellular division, and pathological interaction with the host, suggests that it is not always possible to directly infer functions in Eimeria species from the information gathered in T. gondii [ 7 ].…”