| Marek’s disease (MD) is a neoplastic disease of chickens caused by the lymphotropic alphaherpesvirus, which is called Marek’s disease virus (MDV). It is characterized by T cell lymphoma and infiltration of lymphoid cells into various organs, such as spleen, liver, kidney, cardiac and peripheral nerves. According to the outbreak of recent years, Marek’s disease has been considered to be one of the most serious diseases in poultry infectious diseases.Vaccine is the key to control of the disease. Although by using CVI988/Rispens vaccine, MD has been well controlled. However, there are often reports of Marek’s disease occurred in vaccinated chickens. A CVI988/Rispens vaccinated chickens outbreak MD in a farm at Sichuan province, the morbidity and mortality tates as high as 30% and 20%. Isolation and determination of the virulence and evaluate of isolates by CVI988/Rispens protection assay is very important and significance for prevent MDV in China.Presently, we isolated a MDV wild strain witch adapt to the duck embryo fibroblast from the farm (NC strain) and ascertained to be free from contamination with avian leukosis virus, reticuloendotheliosis virus, and MDVs of other serotypes. Through analysis the Meq gene, abserve the genetic variation of the virus, evaluation the protective effect about CVI988/Rispens and HTV vaccine on SPF chickens. The results showed that Meq amino acids in 71,80,115,139,176 mutations in accord with the characteristics of domestic virulent MDV. The virus is tested for virulence by inoculation at 7 days of age into laboratory strain SPF chickens of four types:challenge group, vaccinated with turkey herpesvirus (HVT) + NC group, vaccinated with CV1988/Rispens + NC gorup, the unvaccination and unchallenged group. The results showed that morbility of chickens with HVT+NC group is 40%, mortality rate is 6.9, tumor incidence is 6.9, protection index is 58; morbility of chickens with CVI988+NC group is 51.7%, tumor incidence is 34.5, mortality rate is 20.7, protection index is 43; morbility of chickens of challenge group is 93.3, mortality rate is 36.6, tumor incidence is 50.0; morbility of chickens of unvaccination and unchallenged group is 83.3, mortality rate is 66.7, tumor incidence is 34.5. Virulence of NC strain is between virulent and very virulent. The protection index with HVT vaccine significant differences CVI988/Rispens vaccine (P<0.05), morbidity and mortality associated with the challenge control group had no significant difference (P> 0.05), HVT vaccine protection force higher than CVI988/Rispens vaccine, it is different between the other reports. In this experiment, CVI988/Rispens vaccine is repeatedly passaged, whether the vaccine can not protected by the invasion of virulent and very virulent strains after repeated passageing, or the strain antigenic variation leads to decreased immune protection force. Blood and feather pulp monitoring showed that after challenge 7-60d can be stable detection detoxification. In addition, we find that the tumor mainly occurs in cardiac of chickens which vaccinated with CVI988/Rispens, this result maybe important to research of Marek’s disease virus’s tumorigenicity. |
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