Comparison Of Virus Plaque Measurement And Antibody Induction Of Four Marek’s Disease Commercial Live Vaccines

In recent years, many variant MDV strains were prevalent in chickens that theirvirulence and pathogenicity were enhanced. Although chickens were vaccinated, the MD wasstill outbreak. The evolution of MDV strains and vaccine failure could result in a significanteconomic loses in poultry farming. The national standard content of CVI988/Rispens, usuallychoose for prevention and control MD, was2,000PFU/mL. The virus titer of MD livevaccine is a very important factor for inducing protective antibody in chicks. However, thedosage of commercial live vaccines from each manufacturer is usually different. Therefore,the virus titrations of commercial live vaccines and induction of antibody need to beevaluated that will be provide clinical guidance for the immunization and prevention of MD.1. In this study,16samples of four batches of commercial vaccines (CVI988/Rispensstrain) from four manufacturers (A, B, C, D) were selected and examined in chicken embryofibroblast cells (CEF) for viral titers by plaque assay. The PFU average showed that virustiters of the four vaccines A, B, C and D reached the national standard2,000PFU/mL, whichwere4,088PFU/mL,3,975PFU/mL,9,475PFU/mL and6,338PFU/mL respectively.2. The internal reference standards (IRS) are different between four manufacturers. TheIRSs of manufacturer A and B were4,000PFU/mL. The IRSs of manufacturer C and D were10,000PFU/mL and6,000PFU/mL, respectively. The differences of virus titers were notsignificant between IRSs provided by the manufacturers and our results. Base on IRS, thequalified rates of manufacturer vaccine A, B, C and D were75%,50%,0%and100%,respectively. Only the vaccine C did not reach its own manufacturer’s standard. Comparisonof actual viral titers and IRS, The coincidence rate of manufacturer A, B, C and D were100%、99%、95%and100%.3.1day old chicks were immunized by different vaccines, and antibody levels were detected by ELISA at day1,7,14and28to arrive at the antibody variation law of different PFUvaccine-induced. The results showed that the induced antibody levels shown in manufacturerswere C> D>A. The results indicated that high virus contents of vaccines can induce high level of antibody in shorten time after immunization, improving the effectiveness of MD’s earlyprevention.