Replication Kinetics Analysis Of Marek's Disease Virus In Chickens

Marek's disease virus serotype 1 (MDV1) is the etiologicalagent of Marek's disease (MD)-a highly contagious, malignant T-lymphomatosis of chickens. Pathopoiesis mechanism of MDV is very complicated, and not be understood exactly. But some researches show that replication of MDV1 in chickens has great relationships with its pathogenicity and horizontal transmission. Increased early viral replication rate is associated with increased virulence of MDV and with MD-related mortality.8 MDV1 strains included strain 814(an avirulent strain used vaccine against MD), strain J-1(a virulent MDV1 researched exactly before)and other 6 isolations isolated from different areas of China , infected SPF chickens experimentally for one group each. We sampled regularly up to 28 days post-infection (d.p.i.). Kinetics of replication of those MDV1, were examined in peripheral blood lymphocyte (PBL), feather tips, spleen, thymus, liver, kidney and brain by using TaqMan Probe duplex fluorescent quantitative polymerase chain reaction(FQ-PCR) method to quantify MDV1 genomes as copy number per million host cells.The results were as follow: 1. Virus load of all strains in feather tips began to raise at 7 d.p.i., and reached the highest at about14～21 d.p.i.. The peak of virus load was about 102～104 fold greater than in early infective stage (1～7 d) , and virulent strains could reach 107 copies/106 cells. Compared with other tissues and organs, virus in feather tips had higher replication levels after 14 d.p.i.. 2. During the cytolytic phase of infection, virus levels peaked in the spleen and thymus, and virulent strains could reach 107 copies/106 cells. 3. Compared with avirulent strains, virulent strains had higher replication levels.We systematicaly drew the replication kinetics curves of a avirulent MDV strain, vMDV or vvMDV strains, including standard strain J-1 and 6 isolations in recent years, in some kinds of tissues or organs. Through analysis we came to the conclusions: The pathogenicity of MDV1 had a great relationship with its replication. Current MDV1 isolations replicated fast, and caused high virus load in chickens. During the cytolytic phase of infection, virus levels peaked in spleen and thymus. Virus had higher replication levels in feather tips than in other tissues or organs after 14 d.p.i.. In generally, MDV load reached 106 copies/106 cells mean the chicken had been infected with virulent MDV, and this could be used as one index of MD diagnose.This article researched the replication kinetics of MDV1 with different pathogenicity including 6 new isolations of China, which kind of work had not been done before. It's a systematically research, including the replication kinetics of MDV1 in different tissues and organs. It provided signigicant datas for the research of MDV1 pathogenic mechanism, diagnose and new vaccines.