| Avian encephalomyelitis (AE), i.e. Epidemic tremor, caused by Avian Encephalomyelitis virus(AEV), is a worldwide infectious viral disease which is characterized by neurological signs such as ataxia, paralysis and tremors of the neck and head. It not only causes the chicken loss but also can make the decrease of hen reproduction. AE often breakouts suddenly and the duration is hard to be forecasted, so it has been one of the main viral diseases which threatens the poultry breeding of the world. At present AE has no effective treatment, and its prevention can only depends on the vaccines. The inactivated vaccine is not used wildly for its shortcomings such as the prolonged antibody production, the shorter immunological length, the higher cost and the troublesome in use. On the contrary the live vaccine can be easily and effectively given by water and their offsprings can attain passive immunity via the maternal antibody. Now the live vaccine is used in many countries. At present, the attenuated vaccines used are maily from abroad and ther is not successful report of its preparation in China. The high cost limited its widely application. Therefore developing of our own attenuated vaccine can not only control the incidence of AE, but also save foreign exchange expenses, and it has large economical benefit. Based on the identification of an AEV Strain isolated from our country, the virulence of the strain was determined, indicating that it is an attenuated strain, from which the attenuated vaccine was prepared. The paper is divided into three parts: The first part is the identification of the AEV-HD strain used in this test: the general identification were conducted, such as physical and chemic characters, hemagglutination trial (HA) and the virus conformation. The results showd that the characters of AEV-HD were stable, its rivulence wasn't influenced by Trypsin, Aether, Chloroform and temperature (57 ℃1 h), could not agglutinate gallinaceous erythrocyte. The virus presents iniquitous rotundity with a simillar size. The diameter was 25~30 nm observed under transmission electrical microscope. Meanwhile, a pair of primers were designed according to the published AEV gene for RT-PCR identification, and the purpose gene section of 900bp was gained. These results proved that AEV-HD is a strain of AEV. The next,AEV-HD's speciality and virulence were checked: AEV-HD was mixed with anti-AEV antibody positive serum at at 37℃for one hour, then the mixture was inoculated to a group of 6-day old SPF chicken embryos by yolk bag, and the AEV-HD alone was also inoculated to another group as controll. As a result, the incidence of AE in the mixture group's chicken was 10% after birth, while the AEV-HD group was up to 75%. This showed that AEV-HD can be neutralized by AEV antibody. Also AEV-HD didn't present the significant pathological changes to embryos, the average brain index of these embryos was 4.65% being closed to the healthy embryos(4.67%), but the index of AEV-VR was 3.67%, and the pathological changes were very obvious. One-day old SPF chicken didn't show AE symptom untill on the tenth day after inoculated AEV-HD into brains, while the chicken incubated with AEV-VR showed the symptom on the fourth or fifth day, indicating that the AEV-HD was a weak strain. The last part is the preparation of attenuated vaccine of AEV-HD. At first, the virus purity was examined according to the quality standard of animal biological produce of the People's Republic of China. The results showed AEV-HD was pure, it wasn't contaminated by bacteria,mycoplasma and other viruses. So attenuated vaccine of AEV-HD was prepared and its immunity was examined. The result of safety test indicated that 8-week old SPF chicken presented no abnormal behavior after taken orally 10 doses of the vaccine (1000 EID50 per does). the efficacity trial showed that the ratio of 8-week old SPF chicken producing AE antibody in the second week after taken orally one doses of the vaccine was 75%, up to 100% after 3 weeks. All the immunized chicken didn't get sick after challeged with AEV-VR in brain. There is no significant difference of antibody levels between the attenuated AEV-HD vaccine and the imported 1143-strain vaccine. Thus, we could safely get the conclusion that the AEV-HD attenuated vaccine is safe and has considerable immunological efficiency. From the results above, AEV-HD was a strain of AEV, and its weak virulence fit with the requirement of attenuated vaccine; the prepared vaccine was safe, the immuno-activity and immunological efficiency were satisfied. This test offered basic for AEV attenuated vaccine and prevention of AE in China.
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