| Rabbit coccidiosis is one of the most common protozoan diseases in rabbits worldwide.To date,11 species have been found to cause this disease,and all of them belong to family Eimeria,in which Eimeria stiedai colonize the bile duct epithelial cells of the liver,and other species usually parasitize in the epithelial cells of the intestinal mucosa.Rabbit coccidiosis is a common and serious disease,with high morbidity and mortality,that has serious impact on the development of the rabbit industry.As one pathogeny of rabbit coccidiosis,E.intestinalis is characterized by strong fertility and high virulence,and rabbit infected with E.intestinalis experience symptoms such as diarrhea,dry excrement,and constipation without feces,and even death in severe cases.In this study,a precocious Line of E.intestinalis was selected from the E.intestinalis Guangxi field strain by serial passages through rabbits of the first oocysts produced during infection,and the comprehensive biological characteristics and immunoprotective effects of this precocious line were studied,which would provide a foundation for the development of live attenuated coccidia vaccines.First,a precocious line of the E.intestinalis Guangxi strain was passaged and selected,after 20 generations of early maturation,and the latent period of the E.intestinalis Guangxi strain was shortened,from 198 h to 148 h.This early-maturing strain was identified by a specific PCR method,and the strain was judged to be a single species;therefore,a precocious lines of the E.intestinalis Guangxi strain was successfully obtained.The second part of this study was to determine the biological characteristics of the precocious lines of the E.intestinalis Guangxi strain,including the latent period stability,oocyst morphology,fertility,ovulation and virulence.The latent period of this strain was determined to be stable,at 148 h,primarily parasitizing the middle and posterior segments of the small intestine.The oocysts were pear-shaped and had oocyst residue after sporulation.The size was 24.1-33.8?m×16.3-23.4?m,the shape index was 1.40 to 1.56,the peak of ovulation was 9 to 11 days after infection,and the fertility was strong.The infection of 1×10~4 sporulated oocysts per rabbit resulted in the ejection of 10~9-grade oocysts.The pathogenicity of the precocious stain was significantly lower than that of the parent strain.When both strains were infected at 3×10~3 sporulated oocysts per rabbits,the weight gain of the precocious strain group was 44.8 percent higher than that of the parental strain group.In the parental strain group,the feces of the rabbits were basically abnormal,and diarrhea was predominant.In the precocious line group,the feces were normal and no diarrhea occurred.The third part of this study was to determine the immune protective effect of the precocious line of E.intestinalis,including the optimal immunization dose,the immunization period and the immunization duration.Throughout the study,it was found that the precocious line of E.intestinalis had good immunogenicity,and the optimal immunization dose was 200 sporulated oocysts per rabbit.14 days post immunization.The rabbits were challenged with a virulent strain of E.intestinalis virulent strain 14 days post immunization.Compared with the control group,the status of the mental state,appetite,and feces were relatively normal in the immunized group.The weight gain results showed that the relative weight gain rate of the immunized group was 22.5 percent higher than that of the control group,and the relative OPG reduction rate was 94.2 percent.In addition,the test results showed that the precocious line of E.intestinalis could produce good immunity on the 11th day after immunization,and the immunity protection could last until the end of the breeding period(70-90 days old). |
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