Studies On UV-attenuated Eimeria Tenella YL Strain And Its Biological Characteristics

Eimeria tenella, which caused avian coccidiosis characterized by poor weight gain and inefficient feed conversion, is a parasitic protozoan belonging to the Phylum Apicomplexa and the most pathogenic species of Eimeria. Currently, some degree of resistance to all anticoccidial drugs has developed, and the reports of drug-residues in food have heightened the consumer's concerns. Live attenuated parasites of several species were proved to be effective in preventing coccidial infection. The physical methods of attenuated oocysts were mainly refrigeration, heat, ultrasonic and radicalization etc. In order to achieve purified attenuated vaccines, the experiments were conducted to research the effects of ultraviolet(UV) radiation on the E. tenella Yangling(YL) strain and separate and analysis the biological characteristics of the attenuated strain. The results as followings:1 When chicken oocysts of E tenella YL Strain were exposed to different amount of ultraviolet ray which wavelengh was 2650 ?, the percentage of sporulation was observed to analyse the attenuated function to vaccine . The results showed that the relative percentage of sporulation with different UV-time (10 min,20 min,30 min,40 min,50 min,60 min)were 94.39%,81.63%,72.96%,53.06%,21.94%and 8.16%,respectively. With the prolongation of UV-time, the relative percentage of sporophyte was dramatically decreased, meanwhile the development of oocysts was obviously effected. It suggested that appropriate UV-time was about 30min when chicken oocysts of E. tenella YL strain were discontinuously exposed to different amount of UV.2 The sporocysts in irradiated oocysts has good definition after cultured for several hours. By determined percentage of relative weight gain, livability, score of cecal lesions and OPG, the results indicated that the activity of oocysts was not significantly influenced by UV-time(10min).With the prolongation of UV-time, the activity of oocysts gradually decreased . In the condition of UV-time(30~40min), the percentage of relative weight gain was about 70%, and the amount of oocysts remained relative level.3 The sporulated oocysts of E. tenella YL attenuated strain were used to infect chickens perorally, then the abundant sporulated oocysts were collected by saturated saline floating measure. The size of the attenuated oocysts was about 19.8~21.2×15.5~16.6μm and the conformation of the strains were integral.4 The prepatent period of E. tenella YL attenuated strain and parental strain were 159 hrs and 168 hrs, respectively, and the period of the attenuated strain shorten about 9 hrs than the parental strain, but which has no significant difference.5 The reproductive potential of single oocyst of the attenuated strains were 2560,1035 and 567 , and the parental strain were 2630,1128 and 708 followed infection dosages increasingly. The results indicated that reproductive potential and infection dosages showed negative relationship and the reproductive potential of the attenuated strains decreased compared with the parental.6 After infected with 1×103,5×103,10×103 attenuated oocysts per chick for 6 d, the percentages of relative weight gain in the experiments were 82.4, 56.2 and 48.5 , respectively. Under the same infection dosage, the score of cecal lesions had different between the attenuated strains and parental strain. The results indicated that the pathogenicity of the attenuated strains was reduced compared with the parental. This study provided the basic materials for further research of attenuated vaccines through radicalization.