Forward genetic analysis of monensin and diclazuril resistance in Eimeria tenella

Eimeria of chickens: the changing face of an old foe

ABSTRACTEimeria are globally enzootic parasites that can cause coccidiosis in chickens. Until recently, remarkably little had changed over the last 40 years in the fundamental biology that underpins detection and control of Eimeria. Tools such as microscopy and lesion scoring remain central to diagnosis, and control still relies on routine supplementation of diets with anticoccidial drugs or application of live vaccines. However, refocusing on aspects of economics, molecular biology, and bacteriology that relate to coccidiosis has prompted considerable change in dogma. The cost of coccidiosis in chickens has been difficult to define, but updating models created in the 1990s suggested an annual cost to the global poultry industry of £10.4 billion in 2016, rising to a peak of £12.9 billion in 2022 under the influence of the COVID-19 pandemic and regional wars. Surveillance using genomic sequence-based diagnostics has suggested the presence of three new Eimeria species, supported by subsequent biological characterization of each line. Use of microbiome sequencing pipelines has revealed the breadth of impact Eimeria infection exerts on enteric microbiota, contributing to dysbiosis and deteriorating litter conditions. Enhanced understanding of Eimeria and the consequences of infection can be used to improve control and diagnosis with relevance to productivity and welfare, creating opportunities to optimize anticoccidial drug use.RESEARCH HIGHLIGHTSThe cost of coccidiosis in chickens fluctuates considerably, peaking in 2022.Three new Eimeria species can infect chickens and escape current vaccines.Eimeria infection exerts wide-ranging effects on enteric microbiota.

Genomic insights into monensin resistance development in Eimeria tenella

Introduction

Monensin resistance in Eimeria tenella poses a significant challenge in poultry farming, compromising the effectiveness of this widely used anticoccidial drug. The present study aimed to identify candidate mutated genes in Eimeria tenella associated with monensin resistance through experimental evolution and pooled genome sequencing.

Methods

The monensin-resistant (MR) strains were rapidly generated by 6 generations of serial passage under gradient monensin treatments using Houghton strain as the parental strain. Genomic sequencing was applied to uncover genetic changes during passages under drug selective pressure. Comparative analysis between resistant and control populations was performed by using the ΔSNP-index and FST values to identify loci with significant selective sweeps. Stringent thresholds were applied to pinpoint candidate genes, followed by annotation and analysis of their potential functions.

Results and discussion

The genetic diversity of MR parasites remained stable across generations, despite varying drug concentrations. Seven candidate genes with 11 missense mutations were identified in MR strains. Key genes include ETH2_0729200 (dynein motor protein), ETH2_0729400 (esterase/lipase), and ETH2_0730000 (pyridine nucleotide-disulfide oxidoreductase) annotated in both the selective sweeps by using ΔSNP-index and FST methods. Further experimental validation of these candidate genes is essential to elucidate their roles in monensin resistance. This research contributes valuable insights into the molecular basis of resistance pressure in Eimeria parasites, potentially informing future strategies for the control of coccidiosis.

Genetic manipulation for the non-model protozoan Eimeria: Advancements, challenges, and future perspective

Eimeria parasites pose a significant global threat to animal health, necessitating improved and cost-effective control measures. Genetic manipulation is pivotal for understanding Eimeria biology and designing targeted control strategies. Recent advancements, including genome sequencing and the development of transient and stable transfection systems, have significantly enhanced insights into the molecular biology of Eimeria. These advancements have paved the way for cutting-edge techniques like CRISPR-Cas9 gene editing. This review summarizes the key milestones in the development of genetic manipulation platforms for Eimeria and their transformative applications, such as the development of next-generation drugs, vaccines, and Eimeria-based vaccine vectors. Furthermore, this review provides insights that could be applicable to the establishment of genetic tools for other protozoan organisms.

Combined transcriptome and whole genome sequencing analyses reveal candidate drug-resistance genes of Eimeria tenella

Avian coccidiosis is a widespread intestinal disease found in poultry that causes substantial economic losses. To extensively investigate the molecular mechanism of drug resistance in Eimeria tenella, we analyzed the sporozoites and second-generation merozoites of drug-sensitive (DS), diclazuril-resistant (DZR) strain, and salinomycin-resistant (SMR) strains of E. tenella through transcriptome sequencing. Whole genome sequencing analyses were performed on resistant strains at different concentrations-11 sensitive strains, 16 field diclazuril-resistant strains, and 15 field salinomycin-resistant strains of E. tenella. Co-analysis indicated that the ABC transporter protein showed differential expression and base mutations in the two resistant strains compared with the DS strain. KEGG pathway analysis demonstrated that the expression of pABAS and HPPK-DHPS, which are associated with the folate biosynthetic pathway, showed downregulation only in the DZR strain with respect to the DS strain. Several key enzymes in the glycolytic pathway were differentially expressed between DS and SMR strains.

Innovative prevention and control of coccidiosis: targeting sporogony for new control agent development

Coccidiosis is one of the most significant diseases affecting the poultry industry, with recent estimates indicating that it causes annual losses exceeding £10 billion globally. Increasing concerns over drug residues and resistance have elevated the importance of safe and effective vaccines as the primary method for controlling coccidiosis and other animal diseases. However, current commercial live vaccines for coccidiosis can negatively impact the feed conversion rates of young broilers and induce subclinical symptoms of coccidiosis, limiting their widespread adoption. Eimeria species, the causative agents of coccidiosis, exhibit unique biological characteristics. Their life cycle involves 2 or more generations of schizogony and 1 generation of gametogony within the host, followed by sporogony in a suitable external environment. Sporogony is crucial for Eimeria oocysts to become infectious and propagate within the host. Focusing on the sporogony process of Eimeria presents a promising approach to overcoming technical challenges in the efficient control of coccidiosis, addressing the urgent need for sustainable and healthy farming practices. This paper systematically reviews existing control strategies for coccidiosis, identifies current challenges, and emphasizes the research progress and future directions in developing control agents targeting sporogony. The goal is to provide guidance for the formulation of scientific prevention and control measures for coccidiosis.

Molecular characterization and analysis of the drug resistance-associated protein phosphoglycerate kinase of Eimeria tenella

Coccidiosis is a parasitic disease caused by Eimeria spp., and the emergence of drug resistance has seriously affected the control of the disease. Using RNA-seq, we previously found that phosphoglycerate kinase of Eimeria tenella (EtPGK) was differentially downregulated in diclazuril-resistant (DZR) and maduramicin-resistant (MRR) strains compared with drug-sensitive (DS) strain. In this study, we further analysed the characteristics and functions of EtPGK to find the possible mechanism of drug resistance of E. tenella. Quantitative real-time PCR (qRT-PCR) and western blot found that EtPGK was highly expressed in sporulated oocysts, followed by sporozoites and second-generation merozoites of E. tenella. Indirect immunofluorescence localization showed that EtPGK was located mainly in the cytoplasm and on the surface of the parasites. Invasion inhibition assays showed that anti-rEtPGK antibody significantly inhibited the invasion of parasites. Further studies using qRT-PCR and western blot found that the transcription and translation levels of EtPGK were downregulated in both resistant (DZR and MRR) strains compared with the DS strain, and the transcription level correlated negatively with the drug concentration. The enzyme activity assay revealed that EtPGK enzyme activity was decreased in the DZR strain compared with the DS strain. qRT-PCR revealed that the mRNA transcription level of EtPGK was significantly downregulated in the field DZR strain and salinomycin-resistant strain compared with the DS strain. These results suggested that EtPGK has other important roles that are separate and distinct from its function in glycolysis, and it might be involved in the development of drug resistance of E. tenella.

Molecular characterization and functional analysis of Eimeria tenella ankyrin repeat-containing protein

Chicken coccidiosis causes disastrous losses to the poultry industry all over the world. Eimeria tenella is the most prevalent of these disease-causing species. Our former RNA-seq indicated that E. tenella ankyrin repeat-containing protein (EtANK) was expressed differently between drug-sensitive (DS) and drug-resistant strains. In this study, we cloned EtANK and analyzed its translational and transcriptional levels using quantitative real-time PCR (qPCR) and western blotting. The data showed that EtANK was significantly upregulated in diclazuril-resistant (DZR) strain and maduramicin-resistant (MRR) strain compared with the drug-sensitive (DS) strain. In addition, the transcription levels in the DZR strains isolated from the field were higher than in the DS strain. The translation levels of EtANK were higher in unsporulated oocysts (UO) than in sporozoites (SZ), sporulated oocysts (SO), or second-generation merozoites (SM), and the protein levels in SM were significantly higher than in UO, SO, and SZ. The results of the indirect immunofluorescence localization showed that the protein was distributed mainly at the anterior region of SZ and on the surface and in the cytoplasm of SM. The fluorescence intensity increased further with its development in vitro. An anti-rEtANK polyclonal antibody inhibited the invasive ability of E. tenella in DF-1 cells. These results showed that EtANK may be related to host cell invasion, required for the parasite's growth in the host, and may be involved in the development of E. tenella resistance to some drugs.

Ponazuril: Clinical efficacy, ultrastructure, and histopathology studies of in vivo anticoccidial action against Eimeria tenella

Ponazuril, a novel antiprotozoal drug in the class of triazine, has shown a promising application on apicomplexan infections in poultry and livestock. However, the effect and mechanism of action of ponazuril against Eimeria tenella (E. tenella) are unclear. The efficacy against E. tenella was initially studied by administering different doses of ponazuril in drinking water. The treated stage and site of ponazuril on E. tenella were observed through ultrastructural and histopathological analyses. Chicks were orally treated with a dose of 15 mg/kg body weight of ponazuril at different endogenous stages of E. tenella post-infection. According to the clinical study, the values of anticoccidial indices (ACI) were 157.0, 162.3, 196.9, 194.5, and 190.9, respectively, when the ponazuril was administered in drinking water at doses of 5, 10, 20, 40, and 50 mg/L for two consecutive days after infection. Among them, the 20 mg/L ponazuril group showed the best anticoccidial effect, which was superior to that of the toltrazuril treatment group, with an ACI value of 191.7. Histological analysis indicated that ponazuril effectively relieved cecal lesions, and decreased the number of merozoites. Transmission electron micrographs (TEM) observed that merozoites became irregular in shape, and some apparent protrusions of the outer membrane were presented especially the second-generation merozoites. Additionally, abnormalities in the development of WFBI and WFBII in the macrogametocyte were observed, which may affect the formation of the ovule wall. Moreover, merozoites in the treated group showed uneven and marginalized chromatin and mitochondrial swelling. These results suggested ponazuril is a potential anticoccidial drug, providing information on the mechanism of anticoccidial effects.

The multifaceted roles of Myb domain-containing proteins in apicomplexan parasites

Apicomplexan parasites are a large and diverse clade of protists responsible for significant diseases of humans and animals. Central to the ability of these parasites to colonize their host and evade immune responses is an expanded repertoire of gene-expression programs that requires the coordinated action of complex transcriptional networks. DNA-binding proteins and chromatin regulators are essential orchestrators of apicomplexan gene expression that often act in concert. Although apicomplexan genomes encode various families of putative DNA-binding proteins, most remain functionally and mechanistically unexplored. This review highlights the versatile role of myeloblastosis (Myb) domain-containing proteins in apicomplexan parasites as transcription factors and chromatin regulators. We explore the diversity of Myb domain structure and use phylogenetic analysis to identify common features across the phylum. This provides a framework to discuss functional heterogeneity and regulation of Myb domain-containing proteins particularly emphasizing their role in parasite differentiation.