Influence Of Marek’s Disease Vaccine Virus On The Infection With The Virulent Virus Strain

Marek’s disease (MD) is a neoplastic disease, which is caused by Gallid herpesvirus type2(GaHV-2) and characterized by neurological disorder, immune suppression and T-cell lymphoma ofchickens. The agent of MD, GaHV-2, which is a member of the Mardivirus genus in the familyHerpesviridae, is also called Marek’s disease virus serotype1(MDV1). MD is a worldwide disease andcauses great economic losses. Though MD vaccines are effective in preventing lymphoma formation inthe history of vaccinology, they still do not completely prevent the infection by virulent strains invaccinated chickens and the virulent virus spreading to the environment. The fact that none of the MDVvaccines induce sterilizing immunity leads to dual or multiple infections by MDVs, which causes theconstant change of the pathogenic processes and the ongoing evolution of MDV. However, theinterference between viruses and the pathogenesis under the condition of dual or multiple infections byMDVs are unclear.There is little specific difference between MDV CVI988vaccine virus and the virulent strains ingenome sequence and common real time quantitive PCR method can’t quantitatively distinguish themwhen MDV CVI988and virulent virus dually infected chickens. In this paper, sequence alignment wasperformed and a method of TaqMan real time quantitive PCR was established with a pair of primers anda probe designed according to the single nucleotide difference in R-LORF2gene for specific detectionof virulent MDV strain L-CY. The recombinant plasmid of MDV L-CY could be detected as lower as20copies while the recombinant plasmid of CVI988couldn’t be detected as much as107copies/μL. TheCV of the intra was no more than3%, indicating that the developed real time quantitive PCR assay isstable. With the method, the virus load of MDV L-CY could be quantified accurately without theinfluence of MDV CVI988.In order to evaluate the influence of MDV CVI988on replication of MDV L-CY, a series of animalexperiments was performed, and the load of the virulent virus at different time in different tissues wasquantified by the real time PCR in chickens under the three condition of infection by MDV CVI988andMDV L-CY at the same time and infection by MDV L-CY at7or14days post infection (dpi) by MDVCVI988. The results showed that in chickens infected at the same time, the virus load of L-CY wasstable at105-107copies/106cells from14dpi to the end of the detection. There was no significantdifference compared to infected-only chickens. This suggested that vaccine virus failed to influence theinfection by virulent strain; however, the virus load of L-CY was less than104copies/106cells under thecondition that the infection by virulent virus was at7dpi by MDV CVI988. This suggested that vaccinevirus inhibited the infection by virulent strain effectively. But the virus load of MDV L-CY in featherpulp was104-106copies/106cells, suggested that the inhibition in feather pulp was not effective;meanwhile, the virus load of L-CY was all less than103copies/106cells under the condition that theinfection by virulent virus was at14dpi by MDV CVI988, which suggested a more effective inhibiton.The real time PCR method for specific detection of MDV L-CY was developed and the influenceof vaccine virus on the infection with virulent virus under the condition of dual infection was analysed systematacially in this paper, which provided the basis for further research of pathogenesis andimmunomechanism of MD.