| Avian encephalomyelitis (AE), also called epidemic tremor, caused by AvianEncephalomyelitis virus (AEV) mianly in chickens under4weeks old, is a worldwideinfectious viral disease which is characterized by neurological signs such as ataxia, paralysisand tremors of the neck and head. It not only causes the chicken loss but also can make thedecrease of hen reproduction. AE often breakouts suddenly and the duration is hard to beforecasted, so it has been one of the main viral diseases which threatens the poultry breedingof the world. At present AE has no effective treatment, and its prevention can only dependson the vaccines. The inactivated vaccine is not used wildly for its shortcomings such as theprolonged antibody production, the shorter immunological length,the higher cost and thetroublesome in use. On the contrary the live vaccine can be easily and effectively given bywater and their offsprings can attain passive immunity via the maternal antibody. Now thelive vaccine is used in many countries. At present, the attenuated vaccines ther is notsuccessful report of its preparation in China. AEV-YBF02strains is provided by QingdaoYebio bioengineering company. The establishment of vaccine of seeds and the determinationof virulence test on YBF02are carried.(1) Virulence determination of AEV-YBF02strains: The results of virulence test on YBF02showed that EID50of AEV-YBF02is5.7.6day-old SPF chick embryos inoculated byYBF02had no distinct pathological changes. YBF02virus and different virulent virus wasinoculated into1day-old SPF chicken by intracerebral passage. The YBF02cause disease atthe tenth day and the other virus cause disease at fifth day. This showed that AEV-YBF02ischicken inoculated into.At the age of6days after inoculation of SPF chick embryos do notcause apparent chick disease. Intracerebral inoculation of1day old SPF chickens in tenthdays before onset, and the virulent strain in about fifth days the pathogenesis. Results indicatethat AEV-YBF02is a weak virus strain.(2) Master stocks of AEV is established. To ensure the quality of vaccine, we carry out the research on seed batch, before we begin to use thevirus to study AEV live vaccine. The AEV-YBF02strain is serial-passaged in SPF chick brainwith12generations, and then is serial-passaged in SPF chick embryos with6generations.EID50of each generation is tested. The bacteria, mycoplasma and exogenous virus detectionare carried out. We do the specificity test, virulence test of the second, fifth, tenth, fifteenth,eighteenth generation. The results show that the virus has no reversion phenome duringsubculture. EID50of each generation has no significant change and virus is pure. The second,fifth, tenth, fifteenth, eighteenth generation have good specificity.(3) Safety and immune efficacy test: based on the master stocks,2,5,10,15,18generations of the strain were inoculated through oral, muscle, wing or thorn to1day oldchickens8~10-week old SPF chicken and180day age chicken, only1day age chickens byoral oncome the disease with incidence of10%, and other ways vaccination different day agechicken will not cause clinical symptoms. On2,5,10,15,18generations of poison toimmune efficacy trials, by the poison oral immune8~10–week old chicken, free after21days to all the antibody test positive, from12weeks until antibody remain high levels. At thesame time avoid after21days, with AEV-VR brain vaccination poison attack, and the resultsshow that each generation time of poison immunogenicity no significant difference, only10immune chicken are more than nine protection that the poison immunogenicity is good, andsubculture each generation to poison kind of immunogenicity have no effect.(4) Virulence reversion test: with AEV-YBF02strains12th generation foundation seedtoxic by the oral method of SPF chickens inoculated with2weeks of age, cohabitation routesof infection for five passages, taking cohabitation infection passaged viruses isolated,respectively intracerebral2-week old SPF chicks, oral vaccination of28-day-old SPFchickens and180days of laying hens. Pathogenicity of the generations is poison in theobserved passage of1,28-day-old SPF chickens and laying hens. The results showed that thevirulence of each generation is basically the same, virulence did not return to strong, stillnon-chick embryo to adapt to the poison.According to the results above, YBF02fits the requirements of attenuated vaccine. Theproperties of master stocks are safety, with good immunogenicity and no virulence reversion.Thus the master stocks establidhed with the strain YBF02is able to prepare the vaccineagainst the AEV. |
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