Effect of Vaccination with Different Types and Dosages against a Very Virulent Marek’s Disease Virus Strain

Effect of Vaccination with Different Types and Dosages against a Very Virulent Marek’s Disease Virus Strain

Abstract

In this study, Marek’s disease(MD) vaccines including herpesvirus of turkeys (HVT) vaccine, attenuated serotype 1 Marek’s disease virus (MDV) CVI988 vaccine and nonpathogenic serotype 2 MDV (SB1 strain) culture were used individually or jointly to immunize 1-day-old specific pathogen free (SPF) chickens at different dosages, the immunized chickens were intradermally infected with 2000 plaque forming unit (PFU) of duck embryo fibroblast (DEF) passaged SD2012-1, a very virulent Marek’s disease virus. All chickens of the experiments and control chickens were observed daily throughout the entire experimental period to assess the vaccines efficacy and immunization dose against MDV SD2012- 1 Strain. CVI988, CVI988+HVT and CVI988+SB1+HVT could partially protect chickens against Marek’s disease after infection with SD2012-1. CVI988+HVT and CVI988+SB1+HVT could provide more efficient protection than CVI988 at normal and high immunization dosage. The protection was not fully satisfactory, and vaccines used at high dosage could not provide more than PI 65. Excessive dilution of these vaccines could result in obvious decrease on protection against SD2012-1. In this study, 450 feather pulp samples collected from the dead or living chickens on Day 150 were detected to be MDV positive by polymerase chain reaction (PCR), and the positive rate of MDV was 100%.