A new landscape of rabbit gut microbiota shaped by the infection of precocious parasites of Eimeria intestinalis

Evaluation of the immunoprotective effect of the recombinant Eimeria intestinalis rhoptry protein 25 and rhoptry protein 30 on New Zealand rabbits

BACKGROUND

Rabbit coccidiosis is a parasitism caused by either one or multiple co-infections of Eimeria species. Among them, Eimeria intestinalis is the primary pathogen responsible for diarrhea, growth retardation, and potential mortality in rabbits. Concerns regarding drug resistance and drug residues have led to the development of recombinant subunit vaccines targeting Eimeria species as a promising preventive measure. The aim of this study was to assess the immunoprotective efficacy of recombinant subunit vaccines comprising EiROP25 and EiROP30 (rhoptry proteins (ROPs)) against E. intestinalis infection in rabbits.

METHODS

Cloning, prokaryotic expression, and protein purification were performed to obtain EiROP25 and EiROP30. Five groups of fifty 35-day-old Eimeria-free rabbits were created (unchallenged control group, challenged control group, vector protein control group, rEiROP25 group, and rEiROP30 group), with 10 rabbits in each group. Rabbits in the rEiROP25 and rEiROP30 groups were immunized with the recombinant proteins (100 μg per rabbit) for primary and booster immunization (100 μg per rabbit) at a two-week intervals, and challenged with 7 × 104 oocysts per rabbit after an additional two-week interval. Two weeks after the challenge, the rabbits were euthanized for analysis. Weekly collections of rabbit sera were made to measure changes in specific IgG and cytokine level. Clinical symptoms and pathological changes after challenge were observed and recorded. At the conclusion of the animal experiment, lesion scores, the relative weight increase ratio, the oocyst reduction rate, and the anticoccidial index were computed.

RESULTS

Rabbits immunized with rEiROP25 and rEiROP30 exhibited relative weight gain ratios of 56.57% and 72.36%, respectively. Oocysts decreased by 78.14% and 84.06% for the rEiROP25 and rEiROP30 groups, respectively. The anticoccidial indexes were 140 and 155. Furthermore, there was a noticeable drop in intestinal lesions. After the primary immunization with rEiROP25 and rEiROP30, a week later, there was a notable rise in specific IgG levels, which remained elevated for two weeks following challenge (P < 0.05). Interleukin (IL)-2 levels increased markedly in the rEiROP25 group, whereas IL-2, interferon gamma (IFN-γ), and IL-4 levels increased substantially in the rEiROP30 group (P < 0.05).

CONCLUSION

Immunization of rabbits indicated that both rEiROP25 and rEiROP30 are capable of inducing an increase in specific antibody levels. rEiROP25 triggered a Th1-type immune protection response, while rEiROP30 elicited a Th1/Th2 mixed response. EiROP25 and EiROP30 can generate a moderate level of immune protection, with better efficacy observed for EiROP30. This study provides valuable insights for the promotion of recombinant subunit vaccines targeting rabbit E. intestinalis infection.

Protection against Eimeria intestinalis infection in rabbits immunized with the recombinant elongation factors EF1α and EFG

Eimeria intestinalis is the most pathogenic species of rabbit coccidiosis, causing weight loss, diarrhea, and even acute death. The currently used anticoccidial drugs against E. intestinalis in rabbits are associated with drug resistance and residues. Immunological control might be a potential alternative. We cloned and expressed the E. intestinalis recombinant EF1α and EFG (rEi-EF1α and rEi-EFG, respectively). Rabbits were immunized subcutaneously every 14 days with 100 µg of rEi-EF1α and rEi-EFG and followed by 5 × 104 E. intestinalis sporulated oocysts orally challenge. Serum samples were collected every 7 days to measure the levels of specific antibodies and cytokines. On post-challenge day 14, rabbits were sacrificed and the anticoccidial index was evaluated. The rabbits of PBS challenged groups exhibited anorexia, diarrhea, marked intestinal wall thickening, and white nodules that formed patches, while rabbits from the rEi-EF1α or rEi-EFG challenged group exhibited milder symptoms. The rEi-EF1α group showed a 75.18% oocyst reduction and 89.01%wt gain; the rEi-EFG group had a 60.58% oocyst reduction and 56.04%wt gain. After vaccination, specific IgG levels increased and stayed high (P < 0.05). The IL-4 and IL-2 levels of rEi-EF1α immunized groups showed a significant increase after immunization (P < 0.05). Both rEi-EF1α and rEi-EFG could induce humoral and cellular immune responses. In contrast, rabbits immunized with rEi-EF1α were better protected from challenge by E. intestinalis than rEi-EFG.

Alterations in the jejunal microbiota and fecal metabolite profiles of rabbits infected with Eimeria intestinalis

Background

Rabbit coccidiosis is a major disease caused by various Eimeria species and causes enormous economic losses to the rabbit industry. Coccidia infection has a wide impact on the gut microbiota and intestinal biochemical equilibrium. In the present study, we established a model of Eimeria intestinalis infection in rabbits to evaluate the jejunal microbiota and fecal metabolite profiles.

Methods

Rabbits in the infected group were orally inoculated with 3 × 10³E. intestinalis oocysts. On the eighth day of infection, jejunal contents and feces were collected for 16S rRNA gene sequencing and liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis, respectively. Jejunum tissues were harvested for hematoxylin and eosin (H&E), periodic acid-Schiff (PAS), and immunohistochemistry (IHC) staining.

Results

Histopathological analysis showed that the whole jejunum was parasitized by E. intestinalis in a range of life cycle stages, and PAS staining showed that E. intestinalis infection caused extensive loss of goblet cells. IHC staining revealed that TNF-α expression was higher in the E. intestinalis infection group. Moreover, both the jejunal microbiota and metabolites significantly altered after E. intestinalis infection. At the genus level, the abundances of Escherichia and Enterococcus significantly increased in the infected group compared with the control group, while those of Oscillospira, Ruminococcus, Bacteroides, Akkermansia, Coprococcus, and Sarcina significantly decreased. In addition, 20 metabolites and two metabolic pathways were altered after E. intestinalis infection, and the major disrupted metabolic pathway was lipid metabolism.

Conclusions

Eimeria intestinalis infection induced intestinal inflammation and destroyed the intestinal homeostasis at the parasitized sites, leading to significant changes in the gut microbiota and subsequent corresponding changes in metabolites.

Graphical Abstract

Fecal metabolomic analysis of rabbits infected with Eimeria intestinalis and Eimeria magna based on LC-MS/MS technique

Rabbit coccidiosis is a common parasitic disease leading to economic losses in the rabbit industry. The intestinal flora plays a key role in pathogenesis of coccidiosis, and fecal metabolome mediates host-microbiome interactions as a functional readout of the gut microbiome. In this study, the E. intestinalis-infected and E. magna-infected rabbit models were established to investigate metabolic alterations and metabolic pathways based on LC-MS/MS technique for the first time. Multivariate OPLS-DA analysis was performed to explore differential metabolites. In total, 288 metabolites were detected from infected and uninfected rabbits. The level of 33 metabolites increased and 4 decreased in rabbits infected with E. intestinalis. Eight pathways were significantly perturbed during E. intestinalis infection including biosynthesis of unsaturated fatty acids, fatty acid biosynthesis, etc. After rabbits infected with E. magna, 13 metabolites were altered and 7 metabolic pathways were dysregulated. These metabolites and metabolic pathways were mainly involved in tuberculosis, parathyroid hormone synthesis, etc. Besides, 25 metabolites differed in abundance between E. intestinalis infection group and E. magna infection group, the major perturbed metabolic pathways were lipid metabolism and endocrine system, respectively. In general, it is confirmed that E. intestinalis and E. magna infection destroyed the intestinal flora, which caused corresponding changes in metabolites, and provide novel insights into the molecular mechanisms of rabbit-parasite interactions.