Abstract
BackgroundChicken coccidiosis, caused by the infection of Eimeria species, leads to important economic losses to the poultry industry. Vaccination with attenuated live parasites seems to be the best way to control this disease. Attenuated eimerian parasites with shortened prepatent times show great changes in intracellular development compared to their parent strains but the mechanisms involved in these biological differences are still unclear.ResultsIn this study, we obtained a precocious line of E. maxima by sequential selection of 22 generations of early shed oocysts in chickens and performed a comparative transcriptome analysis of three different developmental stages of the precocious line and its parent strain using Illumina high-throughput sequencing. Our E. maxima precocious line showed decreased pathogenicity, reduced fecundity and a greatly shorted prepatent time of only 98 h. We found that typical gene changes in the stage development from unsporulated to sporulated oocyst and from sporulated oocyst to merozoite were marked by upregulated organelle genes and protein translation related genes, respectively. Additionally, major differences between the precocious line and its parent strain were detected in the merozoite stage, characterized by downregulated genes involved in protein cleavage and DNA replication activities.ConclusionsOur study generated and characterized an E. maxima precocious line, illustrating gene expression landscapes during parasite development by transcriptome analysis. We also show that the suppressed DNA replication progress in the merozoite stage in the precocious line may result in its reduced fecundity. These results provide the basis for a better understanding of the mechanism of precocity in Eimeria species, which can be useful in studies in early gametocytogenesis in apicomplexan parasites.
Highlights
Chicken coccidiosis, caused by the infection of Eimeria species, leads to important economic losses to the poultry industry
This prepatent time was found to be stable as verified in the following three generations (Additional file 1). This resulted in an E. maxima precocious line (BJ-PL-98) with a prepatent time 32 h shorter than the parent strain
Transcriptome analysis revealed that highly expressed translation initiation factors and invading factors in the sporulated oocyst stage of the precocious line may contribute to its shortened prepatent time while the suppressed protein cleavage activities and DNA replication progresses in merozoites possibly result in its decreased fecundity
Summary
Chicken coccidiosis, caused by the infection of Eimeria species, leads to important economic losses to the poultry industry. Coccidiosis leads to hematochezia (even death) and Attenuated live vaccines, composed of different precocious Eimeria species and strains are simple to apply, Hu et al BMC Genomics (2018) 19:699 cost effective and a safe method against coccidiosis [8, 9]. To generate attenuated Eimeria strains, chickens are orally infected with sporulated oocysts. By successive selection of early shed oocysts, precocious lines can be established. These Eimeria precocious lines are characterized by greatly reduced pathogenicity and prepatent time, and have faster asexual stages or deletion of some schizonts generations, and generate fewer merozoites and oocysts [10,11,12,13,14,15,16]. The precocious line reduced prepatent times from ~ 120 h to less than 107 h, showing less reproduction and pathogenicity with equivalent immunogenicity
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