Kinetics of Rispens CV1988 Vaccine Virus in Single and Mixed Infections with very Virulent Marek's Disease Virus in Isa Brown Chickens

We report the kinetics of infections with serotype 1 pathogenic Marek's Disease virus (MDV) and Rispens CVI988 (Rispens) vaccine virus in the same host. We conducted a 2x3 factorial experiment with two replicates testing the effects of vaccination with Rispens (vaccinated, unvaccinated) and challenge MDV (isolates MPF57, FT158 or unchallenged) using 236 female ISA Brown chickens. The chickens were vaccinated at hatch and challenged at day 5 of age, and the experimental duration was to 56 days post challenge. Peripheral blood lymphocytes (PBL) and feather samples were collected at regular intervals during the experiment. Extracted DNA was subjected to two quantitative polymerase chain reaction (qPCR) tests specific for either pathogenic MDV1 or Rispens viruses. The results showed that the Rispens vaccination reduced the pathogenic viral load in PBL by 1.4 logs and feathers by 1.2 logs. The viral load of pathogenic MDV was significantly higher in both PBL (1 log) and feather (1.3 logs) than that of Rispens in co infected hosts. The more virulent isolate FT158 had a significantly higher viral load than MPF57 in PBL (1.1 logs), but not in feather.