| Rabbit coccidiosis is a disease with diarrhea as the main symptom. It caused by one or more species of the genus Eimeria which parasitize on the liver or intestinal epithelial cells of rabbit. Eimeria magna is one of the most prevalent Eimeria species with a high level of pathogenicity, which make great economic impact on rabbit industry.Currently, the control of rabbit coccidiosis in China is mainly relied on the use of coccidoistats, but the rapid emergence of drug-resistance parasites, coupled with the drug residues in meat, increase the risk of human health and become a prominent problem. The research on avian coccidiosis has made great achievements at domestic and foreign. The coccidiosis vaccines have been manufactured and used in chicken farms in China. But the study of rabbit coccidiosis vaccine in China is limited, and no commercial rabbit coccidiosis vaccine is available.In the first part of this study, the prevalence of E. magna of rabbits was investigated from Guangdong, Guangxi and Shandong Province. A total of 936 fecal samples were collected from different breeds and age groups of rabbit in nine different scales of rabbit farms, which distributed in Foshan, Heyuan, Yangchun, Yulin, Guilin and Nanning. The collected stool samples were examined for the presence of oocysts using the faecal flotation procedure with saturated brine, and the rabbit coccidia oocysts were judged to species by their oocyst morphology. The results showed that the overall positive rate of E. magna was 33.11%(310/936). In the different regions, the highest infection rate was 40.06% in Yulin, the lowest infection rate was 12% in Nanning, and the infection rates of other areas were all higher than 20%. In different age groups, the infection rate of immature rabbit was the highest(60.00%), followed by the young rabbit(29.82%), and the breeding rabbits was the lowest(9.52%). In the different breeding scale, the infection rate of E. magna in the large-scale farms was the lowest(26.59%), and the medium-scale and small-scale farmers were higher(27.94% and 40.28% respectively). In the different varieties, Ira rabbit had the highest infection rate of 40.06%, and the Belgian rabbit was as low as 12%, and other varieties were higher than 25%.In the second part of this study, the single oocyst of E. magna was separated and identified, and the biological characteristics of Weifang strain was studied. The Weifang strain of E. magna was isolated from mixed oocysts by using a agarboard method. A pair of primers designed according to the published 18 S r DNA sequence of E. magna and was availiable in the Oliveira's paper were synthesized, and a PCR method was used to amplify the gene fragment for the specific identification and sequencing comparison. the results indicated that the Weifang strain isolated from single oocyst separation was mono-specific species of E. magna. The studies of the basic biological characteristics showed that the prepatent period of E. magna was 140 ~ 142 h, the earliest time of sporation was 32 h, and 45 hours were needed for the sporulation of more than 80% oocysts. One hundred oocysts of E. magna were randomly selected and measured. The oocysts of the Weifang strain were elliptical in shape and had average dimensions of 35.76 ?m×21.91 ?m, and the shape index was 1.63. 40-day-old rabbits were orally inoculated with 500, 1000 or 3000 sporulated oocysts respectively to measure its fecundity, and the results showed that the fecundity decreased with the increase of inoculated sporulated occysts. 40-day-old rabbits were orally inoculated with 10000, 30000 or 50000 sporulated oocysts respectively, and the results showed that E. magna have a high pathogenicity, and the infected rabbits were depressed, loss of appetite and diarrhea. Both the jejunum and ileum were found to have pathological changes. The intestinal serosa of rabbits inoculated with 30,000 or 50,000 sporulated oocysts were obviously hyperemia. The intestinal lumen was significantly expanded, and the wall was thin, and a lot of mucus-like substance and the button-like necrosis were existed. The microscopy of scraped intestinal mucosa showed a large number of schizont.In the third part of this study, the precocious lines of E. magna Weifang strain was passaged and selected, and then the size, the latent period, the pathogenicity and the stability of precocious line were measured and compared with the parental strain. After selection of 27 successive generations, the latent period of precocious strain shortened from 142 h to 130 h, and the average size of the oocysts was 34.41 ?m × 21.13 ?m, and the shape index was 1.63. The comparion of clinical symptoms and weight gain, showed that the pathogenicity of precocious line was less than its parental strain. The comparison of the oocysts shedding showed that the shedding peak of the precocious line appeared on the eighth day post-inoculated, and the parental strain appeared on the ninth day post-inoculated, and the peak value of the parental strain was much higher.This was the first systematic study on the basic biological characteristics of E. magna and its precocious line in China which would laid a foundation on the further research of rabbit coccidiosis vaccine. |
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