Comparision of pathogenicity and horizontal transmission ability between recombinant Marek’s disease virus field strain with REV-LTR and a very virulent reference strain

Abstract:

Abstract： [Objective] GX0101 is a recombinant field strain of Marek’s disease virus (MDV) with a long terminal repeat (LTR) insert from reticuloendotheliosis virus, a chicken retrovirus. In this study, GX0101 strain was compared to a very virulent reference strain Md5 for their pathogenicity and transmission ability. [Methods]MDV genomic DNA in feather tips was tested and compared by dot blot hybridization with MDV specific probe in control chickens kept in the same isolators in which chickens were challenged with GX0101 or Md5. [Results] mortality and tumor rates of GX0101 were 28.6% and 7.1% for SPF chickens viccinated against Marek's disease virus.Mortality and tumor rates of vvMd5 were 63.1% and 19.0% in the same viccinated SPF chickens. Mortality and tumor rates of GX0101 were lower than that of vvMd5. However, horizontal transmission ability of GX0101 was stronger than that of Md5. After 28 days challenged by GX0101, MDV was detected in 6 of 15 samples. after 35 days challenged by vvMd5, MDV was detected in 2 of 14 samples. [Conclusion] Horizontal transmission ability of MDV isolates was not necessarily parallel to their pathogenicity.It is suggesting that the increased horizontal transmission may be one of selective competitive advantages. Such advantages may help recombinant viruses with the LTR-insert become more and more popular gradually in chicken flocks.