Anticoccidial activity of novel triazine compounds in broiler chickens

Anti-Eimeria tenella activity of Ethanamizuril in vitro and in vivo

The prevalence of chicken coccidiosis in the poultry industry is a significant concern, further exacerbated by the emergence of drug-resistant coccidia resulting from the indiscriminate use of medications. Ethanamizuril, a novel triazine anti-coccidial compound, has been used to combat drug resistance. Currently, it is known that Ethanamizuril acts on the second-generation merozoites and early gametogenesis stages of Eimeria. Limited information exists regarding its impact on the early merozoites and exogenous stage of Eimeria. In the present study, the anti-coccidial properties of Ethanamizuril were evaluated both in vitro and in vivo. The in vitro experiments demonstrated that Ethanamizuril effectively inhibits the sporulation of E. tenella oocysts in a dose-dependent manner and significantly reduces the sporozoite excystation rate. Furthermore, in vivo tests revealed that treatment with 10 mg/L Ethanamizuril in drinking water significantly decreased the copy number of first-generation and secondary-generation merozoites in the chicken cecum, indicating that it can inhibit the development of whole schizonts development. Moreover, treatment with Ethanamizuril demonstrated excellent protective efficacy with an anti-coccidial index (ACI) of 180.2, which was manifested through higher body weight gains, lighter cecal lesion, lower fecal oocyst shedding score and reduced liver index. Collectively, this study suggests that Ethanamizuril effectively treats E. tenella infection by inhibiting both endogenous and exogenous stages development.

Inclusion Complexes of Ethanamizuril with β- and Hydroxypropyl-β-Cyclodextrin in Aqueous Solution and in Solid State: A Comparison Study

Ethanamizuril (EZL) is a new anticoccidial drug developed by our Shanghai Veterinary Research Institute. Since EZL is almost insoluble in water, we conducted a study to improve the solubility of EZL by forming inclusion complexes with β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD). In this study, we performed molecular docking and then systematically compared the interactions of EZL with β-CD and HP-β-CD in both aqueous solution and the solid state, aiming to elucidate the solubilization effect and mechanism of cyclodextrins (CDs). The interactions were also examined in the solid state using DSC, PXRD, and FT-IR. The interactions of EZL with CDs in an aqueous solution were investigated using PSA, UV-vis spectroscopy, MS, 1H NMR, and 2D ROESY. The results of phase solubility experiments revealed that both β-CD and HP-β-CD formed inclusion complexes with EZL in a 1:1 molar ratio. Among them, HP-β-CD exhibited higher Kf (stability constant) and CE (complexation efficiency) values as well as a stronger solubilization effect. Furthermore, the two cyclodextrins were found to interact with EZL in a similar manner. The results of our FT-IR and 2D ROESY experiments are in agreement with the theoretical results derived from molecular simulations. These results indicated that intermolecular hydrogen bonds existing between the C=O group on the triazine ring of EZL and the O-H group of CDs, as well as the hydrophobic interactions between the hydrogen on the benzene ring of EZL and the hydrogen of CDs, played crucial roles in the formation of EZL/CD inclusion complexes. The results of this study can lay the foundation for the future development of high-concentration drinking water delivery formulations for EZL.

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.

Distinct non-synonymous mutations in cytochrome b highly correlate with decoquinate resistance in apicomplexan parasite Eimeria tenella

BACKGROUND

Protozoan parasites of the genus Eimeria are the causative agents of chicken coccidiosis. Parasite resistance to most anticoccidial drugs is one of the major challenges to controlling this disease. There is an urgent need for a molecular marker to monitor the emergence of resistance against anticoccidial drugs, such as decoquinate.

METHODS

We developed decoquinate-resistant strains by successively exposing the Houghton (H) and Xinjiang (XJ) strains of E. tenella to incremental concentrations of this drug in chickens. Additionally, we isolated a decoquinate-resistant strain from the field. The resistance of these three strains was tested using the criteria of weight gain, relative oocyst production and reduction of lesion scores. Whole-genome sequencing was used to identify the non-synonymous mutations in coding genes that were highly associated with the decoquinate-resistant phenotype in the two laboratory-induced strains. Subsequently, we scrutinized the missense mutation in a field-resistant strain for verification. We also employed the AlphaFold and PyMOL systems to model the alterations in the binding affinity of the mutants toward the drug molecule.

RESULTS

We obtained two decoquinate-resistant (DecR) strains, DecR_H and XJ, originating from the original H and XJ strains, respectively, as well as a decoquinate-resistant E. tenella strain from the field (DecR_SC). These three strains displayed resistance to 120 mg/kg decoquinate administered through feed. Through whole-genome sequencing analysis, we identified the cytochrome b gene (cyt b; ETH2_MIT00100) as the sole mutated gene shared between the DecR_H and XJ strains and also detected this gene in the DecR_SC strain. Distinct non-synonymous mutations, namely Gln131Lys in DecR_H, Phe263Leu in DecR_XJ, and Phe283Leu in DecR_SC were observed in the three resistant strains. Notably, these mutations were located in the extracellular segments of cyt b, in close proximity to the ubiquinol oxidation site Qo. Drug molecular docking studies revealed that cyt b harboring these mutants exhibited varying degrees of reduced binding ability to decoquinate.

CONCLUSIONS

Our findings emphasize the critical role of cyt b mutations in the development of decoquinate resistance in E. tenella. The strong correlation observed between cyt b mutant alleles and resistance indicates their potential as valuable molecular markers for the rapid detection of decoquinate resistance.

In Vitro Transcriptional Response of Eimeria tenella to Toltrazuril Reveals That Oxidative Stress and Autophagy Contribute to Its Anticoccidial Effect

Intestinal coccidiosis is a common parasitic disease in livestock, caused by the infection of Eimeria and Cystoisospora parasites, which results in great economic losses to animal husbandry. Triazine compounds, such as toltrazuril and diclazuril, are widely used in the treatment and chemoprophylaxis of coccidiosis. Unfortunately, widespread drug resistance has compromised their effectiveness. Most studies have focused on prophylaxis and therapeutics with toltrazuril in flocks, while a comprehensive understanding of how toltrazuril treatment alters the transcriptome of E. tenella remains unknown. In this study, merozoites of E. tenella were treated in vitro with 0.5 μg/mL toltrazuril for 0, 1, 2 and 4 h, respectively. The gene transcription profiles were then compared by high-throughput sequencing. Our results showed that protein hydrolysis genes were significantly upregulated after drug treatment, while cell cycle-related genes were significantly downregulated, suggesting that toltrazuril may affect parasite division. The expression of redox-related genes was upregulated and elevated levels of ROS and autophagosomes were detected in the parasite after toltrazuril treatment, suggesting that toltrazuril may cause oxidative stress to parasite cells and lead to its autophagy. Our results provide basic knowledge of the response of Eimeria genes to toltrazuril and further analysis of the identified transcriptional changes can provide useful information for a better understanding of the mechanism of action of toltrazuril against Eimeria.

Label-free quantitative proteomic analysis of ethanamizuril-resistant versus -sensitive strains of Eimeria tenella

Background

Avian coccidiosis is an important parasitic disease that has serious adverse effects on the global poultry industry. The extensive use of anticoccidial drugs has resulted in an increase in drug resistance. Ethanamizuril (EZL) is a novel triazine with high anticoccidial activity.

Methods

We compared oocyst production and sporulation between EZL-sensitive (S) and EZL-resistant Eimeria tenella strains (R10 and R200) and used label-free quantitative proteomics to identify differentially expressed proteins (DEPs) between these strains.

Results

We generated two EZL-resistant E. tenella strains: strain R10, which was induced using a constant dose of 10 mg EZL/kg poultry feed, and strain R200, which was generated by gradually increasing the EZL dosage to 200 mg EZL/kg poultry feed. With an increase in resistance, the total oocyst output decreased, but the percentage of sporulation did not change significantly. We identified a total of 7511 peptides and 1282 proteins, and found 152 DEPs in the R10 strain versus the S strain, 426 DEPs in the R200 strain versus the S strain and 494 DEPs in the R200 strain versus the R10 strain. When compared with the S strain, 86 DEPs were found to have consistent trends in both resistant strains. The DEPs were primarily involved in ATP and GTP binding, invasion, and membrane components. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses of the DEPs suggested that they are involved in transcription and translation processes. Protein–protein interaction network analysis of the 86 DEPs showed that 10 proteins were hubs in the functional interaction network (≥ 8 edges) and five of them were ribosomal proteins.

Conclusions

The results of the present study indicate that the resistance mechanisms of E. tenella against EZL might be related to the transcriptional and translational processes, especially in the factors that inhibit the growth of parasites. The DEPs found in this study provide new insights into the resistance mechanisms of E. tenella against EZL. Further research on these potential targets holds promise for new chemotherapeutic approaches for controlling E. tenella infections.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05412-6.

Case of necrotic enteritis associated with campylobacteriosis and coccidiosis in an adult Indian peacock (Pavo cristatus)

Background

To date, Campylobacter jejuni has not been found to be pathogenic to peafowl. The available publications show that out of a total of 44 samples tested from peafowl, this bacterium was isolated only in two cases. Eimeria pavonina infestations in the peafowl have been described, but no fatal cases have been reported yet.

Case presentation

The four-year-old peacock was presented with chronic diarrhea, emaciation and weakness. Post mortem examination revealed enlarged and pale kidneys, small intestinal mucosal necrosis and thickening of intestinal wall, and pericardial effusion. The histopathological examination revealed necrotic enteritis with marked mononuclear cells infiltration associated with the presence of coccidia, additionally there was histological evidence of septicemia in liver and kidneys. Bacteria identification was based on light microscopy of the small intestine sample, culture, and biochemical tests. Further identification was based on PCR. Antimicrobial susceptibility profile was created by determination of minimal inhibitory concentration (MIC) values for 6 antimicrobial agents from 5 different classes. PCR assays were performed to detect virulence factors genes responsible for motility, cytolethal distending toxin production, adhesion and internalization. Bacteriology of the small intestine sample showed abundant growth almost exclusively of Campylobacter jejuni, resistant to ciprofloxacin, gentamycin and ampicillin. Bacteria was sensitive to Amoxicillin + clavulanic acid, tetracycline, and erythromycin. All tested virulence factors genes have been detected. The parasitological examination was performed by microscopic examination of fresh faeces and intestinal content, and revealed the moderate number of Eimeria pavonina, Histomonas meleagridis, single Capillaria spp. eggs as well Heterakis spp. like parasites.

Conclusion

The above case shows that a virulent isolate of Campylobacter jejuni in combination with a parasitic invasion may cause chronic enteritis in peafowl, which most likely led to extreme exhaustion of the host organism and death.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03260-1.

Controlling the causative agents of coccidiosis in domestic chickens; an eye on the past and considerations for the future

Coccidiosis is a potentially severe enteritis caused by species of obligate intracellular parasites of the genus Eimeria. These parasites cause significant economic losses to the poultry industry, predominantly due to compromised efficiency of production as well as the cost of control. These losses were recently estimated to cost chicken producers approximately £10.4 billion worldwide annually. High levels of Eimeria infection cause clinical coccidiosis which is a significant threat to poultry welfare, and a pre-disposing contributory factor for necrotic enteritis. Control of Eimeria parasites and coccidiosis is therefore an important endeavour; multiple approaches have been developed and these are often deployed together. This review summarises current trends in strategies for control of Eimeria, focusing on three main areas: good husbandry, chemoprophylaxis and vaccination. There is currently no "perfect solution" and there are advantages and limitations to all existing methods. Therefore, the aim of this review is to present current control strategies and suggest how these may develop in the future.

Absorption and Distribution of Toltrazuril and Toltrazuril Sulfone in Plasma, Intestinal Tissues and Content of Piglets after Oral or Intramuscular Administration

Piglet coccidiosis due to Cystoisospora suis is a major cause of diarrhea and poor growth worldwide. It can effectively be controlled by application of toltrazuril (TZ), and oral formulations have been licensed for many years. Recently, the first parenteral formulation containing TZ in combination with iron (gleptoferron) was registered in the EU for the prevention of coccidiosis and iron deficiency anemia, conditions in suckling piglets requiring routine preventive measures. This study evaluated the absorption and distribution of TZ and its main metabolite, toltrazuril sulfone (TZ-SO₂), in blood and intestinal tissues after single oral (20 mg/kg) or single intramuscular (45 mg/piglet) application of TZ. Fifty-six piglets were randomly allocated to the two treatment groups. Animals were sacrificed 1-, 5-, 13-, and 24-days post-treatment and TZ and TZ-SO₂ levels were determined in blood, jejunal tissue, ileal tissue, and mixed jejunal and ileal content (IC) by high performance liquid chromatography (HPLC). Intramuscular application resulted in significantly higher and more sustained concentrations of both compounds in plasma, intestinal tissue, and IC. Higher concentrations after oral dosing were only observed one day after application of TZ in jejunum and IC. Toltrazuril was quickly metabolized to TZ-SO₂ with maximum concentrations on day 13 for both applications. Remarkably, TZ and TZ-SO₂ accumulated in the jejunum, the primary predilection site of C. suis, independently of the administration route, which is key to their antiparasitic effect.

Pharmacokinetics and anticoccidial activity of ethanamizuril in broiler chickens

The treatment effect of ethanamizuril (EZL) to broiler chickens experimentally infected with 8 × 104Eimeria tenella was evaluated. On the third day after infection, the broiler chickens were treated with EZL by gavage at doses of 2, 4, and 8 mg/kg body weight (bw) for once. For double administration, the challenged broiler chickens were administered EZL at doses of 1, 2, 4, and 8 mg/kg bw by gavage continually on the third day and fourth day and once a day. Throughout the experimental period, performance parameters including body weight gain, mortality, cecal lesion score, bloody diarrhoea and oocyst output were recorded. The anticoccidial efficacy was evaluated using the anticoccidial index (ACI). Meanwhile, the concentrations of EZL in chicken cecal contents were measured, and the data were analyzed with a non-compartmental model. The results indicated that EZL showed good anticoccidial activity at single dose of 4 mg/kgbw, with the corresponding ACI of 175.73. When the challenged chickens were treated with EZL under double administration, the EZL showed a medium level of anticoccidial activity at a dose of 2 mg/kg bw, with the corresponding ACI of 162.48. The maximum concentrations (Cmax) of EZL in content were 2.43 ± 1.16, 4.28 ± 1.56, and 8.57 ± 1.33 mg/kg after the chickens were administrated at doses of 2, 4, and 8 mg/kg bw, respectively. The respective areas under the curve were 36.93 ± 8.91, 96 ± 16.31, and 262.76 ± 51.52 mg/kg h. The respective half-lives (T1/2) were 10.82 ± 2.02, 10.53 ± 2.23, and 10.60 ± 1.50 h. The results show that when the concentrations of EZL in chicken cecal contents reached 4.28 ± 1.56 mg/kg, there is a significant therapeutic effect on chicken coccidiosis.

Evaluation of optimum conditions for decoquinate nanoliposomes and their anticoccidial efficacy against diclazuril-resistant Eimeria tenella infections in broilers

Decoquinate (DQ) is used for prophylaxis against coccidian infections within the digestive tract of chickens, but DQ is extremely insoluble in water. Hence, improving the water solubility of DQ is extremely important. First, decoquinate nanoliposomes (DQNLs) were prepared by the thin-film dispersion-ultrasonic method. The preparation conditions of DQNLs were optimized using the orthogonal test. The optimal preparation conditions of DQNLs were: a ratio of egg-yolk lecithin:drug (w/w) of 10:1, ratio of egg-yolk lecithin:cholesterol (w/w) of 5:1, rotary-evaporation temperature of 50 ℃, and ultrasound duration of 15 min. The encapsulation efficiency of DQNLs prepared under these conditions reached 99.24 % and drug loading was 5.67 %. The characterization of optimized DQNLs was also done. Transmission electron microscopy of DQNLs showed that they had the characteristic structure of liposomes. The mean particle size was 115.6 nm. The polydispersity index was 0.175. The zeta potential was -39.1 mV. The stability of DQNLs was high upon storage at 4 ℃. In vivo studies demonstrated that the lower dose (5 mg/L) of DQNLs in drinking water obtained the similar anticoccidial efficacy to that of 40 mg/kg DQ in feed against diclazuril-resistance Eimeria tenella isolate. The in vitro inhibitory effect of DQNLs on the sporulation of Eimeria tenella oocysts was dose-dependent. Therefore, the anticoccidial efficacy of DQ was enhanced significantly after being encapsulated into nanoliposomes.

Population pharmacokinetics of ethanamizuril in normal and coccidiosis-infected chickens through ultra-performance liquid chromatography-Tandem Mass Spectrometry

Ethanamizuril is a new triazine compound that shows potential for application in novel anticoccidial treatment. In this study, a pharmacokinetic model of ethanamizuril was established on the basis of the blood concentration of 81 experimental animals. The final model showed that ethanamizuril was distributed as a two-compartment model with first-order absorption after oral administration in chickens. Its clearance rate and volumn of central compartment distribution (V_c ) were affected by age and body weight, and volumn of central compartment distribution (V_c ) and volume of peripheral compartment distribution(V_p ) were influenced by weight and infection. External verification revealed that the model had good prediction accuracy and stability.

Preliminary study of the mechanism of action of ethanamizuril against Eimeria tenella

Ethanamizuril (EZL) is a novel triazine compound with excellent anticoccidial activity. We carried out a preliminary investigation of the effects of EZL on the different life cycle stages of Eimeria tenella. EZL mainly acted on the schizogony stage, with peak activity during the second-generation merozoite stage. We also studied the possible target of EZL by identifying the majorly differentially expressed gene affected by EZL in second-generation merozoites using real-time polymerase chain reaction, and screening for surface antigen proteins (SAGs). The relative expression levels of SAGs were compared by Western blot analysis showing that expression levels of surface antigen family member (SAGfm) and SAG19 were significantly downregulated by EZL. Immunofluorescence analysis indicated that SAGfm and SAG19 were localized on the surface of second-generation merozoites. In addition, fluorescence signals were significantly stronger in second-generation merozoites of infected non-medicated control (INC) group compared with that of the EZL group. Therefore, it was speculated that SAGs might be a potential target of EZL action. The inhibitory effects of anticoccidial drugs on SAG levels in coccidia thus warrant further research.

Metabolism, Distribution, and Excretion of Ethanamizuril in Chickens

Ethanamizuril(N-{4-[4-(3,5-dioxo-4,5-dihydro-3H-[1,2,4]triazin-2-yl)-2-methyl-phenoxy]-phenyl}-acetamide, EZL) is a new anticoccidiosis compound and belongs to the class of triazines. In this study, the metabolism, distribution, and excretion of EZL were evaluated in chickens after administration of EZL at a single dosage. According to the relevant drug biotransformation rules, the exact molecular mass detection, the fragmentation characteristics, and the retention times, a total of five metabolites were identified in vivo in chickens, including two phase I metabolites and three phase II conjugated metabolites. The major metabolic pathways of EZL in chickens were deacetylation, hydroxylation, and glucuronidation. Regarding ¹⁴C-tissue residues after administration, kidney was considered to be the target tissue, as ¹⁴C-tissue residues could be detected at 240 h postdose. DeacetylEZL (M3) was the main metabolite, accounting for 68.65% and 25.62% of ¹⁴C in kidney at 6 and 24 h, respectively. In heart, muscle, skin+fat, and lung tissues, EZL was the main radioactive substance accounting for 94.88%, 97.32%, 96.23%, and 91.3% of ¹⁴C, respectively. In the liver, EZL and M3 were 20.76% and 54.65% of ¹⁴C, respectively. In chicken tissues the ratio of M5 was too low to be quantitated and it was mainly detected in chicken fecal and bile samples. In chicken excreta, EZL, M3, and glucuronidation of EZL (M5) accounted for 7.02%, 12.33%, and 10.32% of the dose, respectively and were eliminated primarily. This study presents the first detection of EZL metabolites, which is helpful for further understanding of the metabolic mechanism and in vivo intermediate processes of EZL. The results of this study will be good bases for better understanding EZL's anticoccidiosis mechanism and will serve as a helpful reference for assessing the risks to animals and humans.

Proteomic analysis of the second-generation merozoites of Eimeria tenella under nitromezuril and ethanamizuril stress

Background

Eimeria tenella is a highly pathogenic coccidian that causes avian coccidiosis. Both nitromezuril (NZL) and ethanamizuril (EZL) are novel triazine compounds with high anticoccidial activity, but the mechanisms of their action are still unclear. This study explored the response of E. tenella to NZL and EZL by the study of changes in protein composition of the second-generation merozoites.

Methods

Label-free quantification (LFQ) proteomics of the second-generation merozoites of E. tenella following NZL and EZL treatment were studied by LC-MS/MS to explore the mechanisms of action. The identified proteins were annotated and analyzed by Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and protein-protein interaction (PPI) networks analysis.

Results

A total of 1430 proteins were identified by LC-MS/MS, of which 375 were considered as differential proteins in response to drug treatment (DPs). There were 26 only found in the NZL treatment group (N-group), 63 exclusive to the EZL treatment group (E-group), and 80 proteins were present in both drug groups. In addition, among the DPs, the abundant proteins with significantly altered expression in response to drug treatment (SDPs) were found compared with the C-group, of which 49 were upregulated and 51 were downregulated in the N-group, and 66 upregulated and 79 downregulated in the E-group. Many upregulated proteins after drug treatment were involved in transcription and protein metabolism, and surface antigen proteins (SAGs) were among the largest proportion of the downregulated SDPs. Results showed the top two enriched GO terms and the top one enriched pathway treated with EZL and NZL were related, which indicated that these two compounds had similar modes of action.

Conclusions

LFQ proteomic analysis is a feasible method for screening drug-related proteins. Drug treatment affected transcription and protein metabolism, and SAGs were also affected significantly. This study provided new insights into the effects of triazine anticoccidials against E. tenella.