Studies On The Preparation Of Uv-Attenuated Eimeria Tenella YL Strain Vaccine And Its Preventive Effect

Coccidiosis is recognized as a major parasitic disease of poultry and is caused by the apicomplexam protozoan Eimeria. The annual economic losses of poultry industry in the world is estimated at about US$ 3 billion because of higher morbidity (50%～70%), and the disease has been largely controlled through the use of anti-coccidial drugs added directly into feed. However, coupled with another factor that the question of drug residue in poultry products is increasingly concerned, rapid appearance of resistant Eimeria strains and very few new drugs developed have stimulated studies on alternative control methods, one of which is vaccination with a live vaccine. Therefore, the present studies were carried out to develop new live vaccines against chicken coccidiosis, and the results were as the followings:(1) E. tenella YL oocysts were irradiated in 6 methods by ultraviolet. 8-day-old chickens were infected with irradiated and unirradiated sporulated E. tenella YL oocysts. The dose was 1×10~5. The pathogenicity was determined by examining lesion score, oocysts per gram feces (OPG), relative weight gain rate, mortality, blood feces etc.. The results showed that chickens were affected severely by unirradiated sporulated E. tenella YL oocysts. Symptoms and pathological lesion were serious, and some chickens were dead. The mortality was above 5%. But the pathological effects of irradiated sporulated E. tenella YL oocysts were significantly decreased. In testing groups, the chickens had no death, but many oocysts were found in feces examined by a microscope. The pathological effects of the irradiated sporulated E. tenella YL oocysts in method 5 on chickens were the lightest. Its relative weight gain rate and lesion score were obvious smaller than that of other irradiated groups.(2) The chickens were vaccinated with irradiated sporulated E. tenella YL oocysts prepared in 6 methods, and the optimal attenuated method was chosen. The results showed that, after vaccinated with E. tenella YL strain attenuated in method 5 by ultraviolet ray, the day average weight curve of chickens increased stability, the total oocyst productions were less than that of other experimental and the positive control groups, the OPG value curve was also lower than that of other groups. The histopathological lesions were milder than that of other groups.(3) The chickens were vaccinated with irradiated sporulated E. tenella YL oocysts prepared in the optimum attenuating method, and the optimal vaccination dose was chosen. The results showed that, the relative weight gain rate was higher than that of other groups, and the OPG value and histopathological lesions were less than that of other experimental and the positive control groups when immunizing dose was 8000 sporalated oocysts per chicken.(4) The chickens were vaccinated with irradiated sporulated E. tenella YL oocysts prepared in the optimal attenuated method, and the optimal vaccination age was chosen. The results showed that, the relative weight gain rate and survival number were higher than that of other groups and the OPG value and caecal lesion score were lower than that of other groups when the chickens was first vaccinated at 9 days old.(5) The chickens were vaccinated with irradiated sporulated E. tenella YL oocysts prepared in the optimal attenuated method, to show the number change of T cells in the lymphatic organs of the chickens after vaccination by acid-α-naphthylacetate esterase (ANAE) staining, in order to provide the histologic groundwork for the study of immunologic mechanism of vaccines against avian coccidiosis. The results showed that the numbers of T cells in thymus, spleen and cecal tonsil of the experimental group were higher than that of control group. But the crest-time and peak value in each group were different. The crest-time of the thymus was the earlist, it appeared at the 7 d after second vaccination, the peak value was 118 /100μm~2. The next was the cecal tonsil, the crest-time was at the 10 d after second vaccination, and the peak value was 64/100μm~2. The crest-time of the spleen was the last, it appeared at the 14 d after second vaccination, and the peak value was 83/100μm~2.