Investigation Of Avian Encephalomyelitis In Shaanxi Province And Study Of The Methods Of Its Diagnosis And Control And Isolation And Identification Of Its Virus

Avian Encephalomyelitis (AE) in 24 groups of chicken from Baoji and Weinan regions of Shaanxi province was investigated. All stocks involved had the history of the disease or a decreasing egg laying with average reducing extent of 17.2%. 256 serum samples from the stocks were tested with Agar Gel precipitin (AGP). It showed that 85.6% of the chickens were AE positive in average, especially 100% in 10 stocks. Further detection in 2 groups of breeding chickens indicates that the chicken appeared the clinical symptoms of AE in 3 days after hatched. The brain sample preparations from the sick chicken were injected into chicken embryos of 6 days to isolate the virus which were tested to be positive for AE using AGP and embryo virus neutralization test from the third generation. Neutralization index was 316.Purified with the method of differential centrifugation and stained with 1% sodium phosphotungstate, the morphometrics of the isolated virions were observed under the transmission electronic microscope, it shows that the virion takes the shape of hexagon or near circular, without envelope and varies from 25nm-30nm in size. The physicochemical and physical properties characterize that the virions were resistant to aether, chloroform, acid and trypsin, as well as to the heat at 50癈, 60min. The same cases as the primary affection are able to duplicate when the 1 day old chickens were inoculated with the virus, further, the typical symptoms of AE were observed in 3 months roosters infected with a large doses of the isolated virus. The most typical histopathological changes in infected chicken were as follows: the non-purulent encephalomyelitis in the central nervous, the hyperplasia of the glia cells and perivascular cuff in cerebrum and the aggregation of lymphocytes within the gizzard, glandular stomach, duodenum and pancreas which were of the unique diagnosis significance. The results indicated that the isolate is the AE virus.The isolate virus strain was injected into chicken embryo yolksac of 6 days. And its brains gastrointestinal tracts and pancreas of the embryos were collected at 16 days. After homogenization and inactivation, They were used as the AGP and produced specific precipitate line with the AE positive standard serum, while with ND, EDS-76, AI, IB positive serum and the serum from SPF chicken had no precipitate line. The antigen was used to test 60 serum samples. 48 of them were AE positive, just the same as that from the standard AE antigen.The antigen prepared through inoculating the isolated virus into chicken embryos of 6 days and chickens of 1 day was used to make inactivated vaccine by mixing and emulsifying with oil at a proper proportion. The effects of the vaccine were compared with the AE attenuated vaccine imported abroad by vaccinating the male Nico chickens of 1 Id separately. It results that the levels of the specific antibody against AEV reached its peak on 30d after inoculated, presenting no prominent difference in the antibody level between the two vaccines (P>0.05). All the chicken above were inoculated with the isolated virus at 50d post-immunization, no anomaly was observed in the vaccinated groups and the control group of the AE attenuated vaccine 25d thereafter, while 8 chicken in the control group of the inactivated vaccine revealed slight clinical symptom of AE. By AGP test, the brain and pancreas of the sick chicken were detected to be AE. Further more, the 18 flocks inoculated and their next generation were investigated no AE occurred during the 2 years, while AE occurred in some chicken flocks juxtaposing the 9 tested chicken houses inoculated the activate vaccine or no vaccinating was done. Therefore, the inactivated vaccine prepared is of security, effectivity, and can be used to prevent the occurrence of AE.