Study On The Safety Inspection And Immunoprotection Of Eimeria F₂,An Attenuated Vaccine Strain

Coccidiosis is one of primary poultry parasitosis, which has a wide range of distribution, high frequency of incidence and also causes large economic loss. This disease mainly outbreaks in domesticated chicken populations, and caused all global farmers of poultry a loss of3,000,000,000U.S. dollars every year. As one of seven coccidians species which can lead to chicken coccidiosis, Eimeria tenella is the most pathogenic and the greatest harmful, as well as the most important pathogen for chicken coccidiosis. At present there are two methods to control coccidiosis, one is the vaccine and the other is the drug. As a result of drug resistance caused by widely used of coccidiostats, as well as the demand for green food, the use of coccidiostats has been restricted. Therefore the vaccination of coccidian vaccine is now and also will be the main method to prevent the disease in the future.In this research the optimum immune dose, security and immune protection period of attenuated vaccine, Eimeria tenella strain F2, have been evaluated. The results showed that the vaccine has the ability to protect chickens to live Eimeria tenella infection effectively, when the number of oocyst in oral vaccine has reach4000/each. And when the dose of vaccine was more than4000oocysts/each, the antibody titer of experiment chickens had no significant increase. It means that the optimum immune dose of vaccine, Eimeria tenella F2which break by ultrasonic, is4000oocysts/each. After immunized ten times optimum immune dose,4×104oocysts/each, growth rate of experiment chickens had no significant difference to the control group, and there was no lesions in the intestinal, as well as oocysts excreted in feces. It means that the security immune dose of the vaccine is4×104oocysts/each the following. The oocysts were test under microscope as well as the animal challenge experiment after the re-sporulation of Eimeria tenella strain F2which attenuated by ultrasonic. There was no sporulated oocysts has been found after tested under microscope. After challenged with re-sporulation of Eimeria tenella strain F2, the experiment chickens grew normally, and there was no oocysts excreted in feces, as well as lesions in the intestinal. It means that the vaccine does not have phenomenon of atavism. After evaluation of the immune protection period, the result showed that the immune protection period of the vaccine was more than59days. By using the method of ELISA, the titer of antibody in the immune period was more than 31.5ng/L after immuned. The titer of antibody was higher and the range of change was small, and the vaccine has the ability to protect chickens to against the infection of Eimeria tenella.