Studies On Immunogenicity And Safety Of E.Acevulina Precocious Strain In Chicken

This study is to discuss the immunogenicity and safety of E. acevulina precocious strain in chicken to provide a basis for clinical application of E. acevulina precocious strain. According to the veterinary biological products experimental study technology guidelines of department of agriculture and the indicatores of duodenum lesion score, oocyst decrement, relative weight gain rate, reduction of lesion scores (RLS), and anticoccidial index (ACI), we made the basic test on identification, efficacy, periods of immune producing and duration, stability, safety and virulence return of the vaccine. Researches show that:(1) Morphological characters of precocious and parental strains:①The unsporulated oocyst size of E. acervulina precocious strains is15.2±2.3u m×13.3±1.9μm and its shape index is1.15. The sporulated oocyst size of precocious strains is19.2±2.4μm×15.9±2.1u m and its shape index is1.17. The latent period of E. acervulina precocious strains which is mainly on the duodenum and upper middle of jejunum is77h and the shortest sporulated time is17h.②The unsporulated oocyst size of E. acervulina parental strains is17.0±2.1μ m x14.1±1.4μm and its shape index is1.21. The sporulated oocyst size of parental strains is19.4±2.8μm x15.8±2.4u m and its shape index is1.23. The latent period of E. acervulina paretal strains which is mainly on the duodenum and upper middle of jejunum is96h, and the shortest sporulated time is17h.(2)1to6-day-old chicken were immunized400oocysts per chick first respectively, then were immunized800oocysts per chick again after10days. Age of chicken with first immunization increasing, the average lesion scores decreased, while the average weight gain, relative weight gain rates and ACI increased. When the chicken were immunized first at4to6days, its average lesion scores were1or less, reductions of lesion scores were70%or more, mortalities were0%, relative weight gain rates were80%or more, oocyst decrement rates were75%or more, and ACIs were180or more, suggesting that protective effect of immunization is well and the minimum of first immune day is on the4th day age.(3) Using different doses to the second immunization on the14th day, when the doses were400oocysts per chicken or more, the average lesion scores of immune groups were1or less, reductions of lesion scores were70%or more, mortalities were0%, relative weight gain rates were80%or more, oocyst decrement rates were75%or more, and ACIs were180or more, suggesting protective effect of immunization is well. Second immunizations were done every3to11days after first immunization respectively, and all immunized groups could attain good immune efficacy. The relative weight gain rates were90%or more and ACIs were185or more in the groups immunized for the second time every7to11days respectively. All the results show that the minimum dose of secondary immunization is400oocysts per chick, and the best interval between first and second immunization is7to11days.(4) Chicken infected by parental strains respectively on the3rd,5th,7th and9th day after first immunization, the relative weight gain rate, oocyst decrement, RLS and ACI were increasing gradually in immunized groups. On the9th day after the first immunization, the weight gain rate attained to76.6%, the oocyst decrement rate was73.4%, the average lesions score was1.4, RLS was60%and ACI was161.7in the immunized group, showing that the organism had partly immune protection on the9th day after first immunization. Chicken infected by parental strains respectively7th,14th,21st,28th and35th day after second immunization, the oocyst decrement rates were86%or more, RLSs were74%or more, ACIs were183or more in immunized groups and all immunized groups attained good immune efficacy, confirming that the organism can obtain good immune efficacy on the7th day after second immunization, and immune protection is sustainable for35days (49-day-old).(5) The vaccine strain liquid was orange and homogeneous maitained for12months at2to8℃avoiding light. Yellowish green precipitatioin of oocysts was in the bottom of the bottle, but disappeared after shaking. Within the prolong of the preservation, the relative weight gain rates, oocyst decrement rates, RLSs and ACIs were on downward trends, and the average lesions scores were on upward trends. The vaccine strain liquid preserved within six months had good immue efficacy, with the average lesions score being less than1, mortality being0%and ACI being180or more. We demonstrate that precocious strain of E. acevulina is stable, whereas the effective tend of the vaccine is reduced along the extension of saving time.(6) The chicken intestinal injury was slight, the lesions score was1or less and the relative weight gain rate attained to80%via the tests of single-dose vaccination safety, single-dose repeat vaccination safety and overdosage vaccination safety, showing that chicken coccidiosis vaccine (precocious strains of E. acervulina) achieve the vaccine safety requirements.(7)4batches of E. acervulina precocious strain with serial passage for5times were selected to perform the tests in the terms of oocyst content, mature rate, safety, immunogenicity and purity, showing that the oocyst content was30.0±2.2×105oocysts/bottle, mature rates were80%or more. Sterile test proved there was no bacterial growth in precocious strain. The duodenum lesions score was1or less, the mortality rate was0%and the relative weight gain rate was80%or more on safety test. Within groups immunized by selected strains, lesions scores were0.6or less with no significant difference (P>0.05), RLSs were80%or more, oocyst decrement rates were85%or more, and all groups attained good immune efficacy. Our data show that the original precocious strain of E. acervulina has genetic stability, conforms to the features of original seed (the precocious strains of E. acervulina), and has no sign of virulence return.