Several highly efficacious
vaccines are currently available for control of
Marek's disease, a lymphoproliferative disease in chickens. However, these
vaccines are unable to prevent
infection with
Marek's disease virus (MDV) in vaccinated birds. This leads to shedding of virulent MDV from feather follicle epithelium and skin epithelial cells of vaccinated and infected chickens. The objective of the present study was to study the interactions between a
vaccine strain (CVI988/Rispens) and a very virulent strain of MDV (RB1B) in feathers. We examined genome load and replication of CVI988 and MDV-RB1B strains at various time points post
infection. Moreover, we evaluated
cytokine expression in feathers as indicators of immunity generated in response to
vaccines against MDV. Analysis of feathers collected between 4 and 21 days post
infection (d.p.i.) revealed a steady level of CVI988 genome load in the presence or absence of RB1B.
Infection with MDV resulted in a significant increase in RB1B genome load peaking at 14 d.p.i. Importantly, vaccination with CVI988 resulted in a significant reduction in accumulation of MDV-RB1B in feathers. RB1B genome accumulation in feather
tips was associated with increased expression of
interferon-α at 14 d.p.i. and
interferon-Sγ at earlier time points, 4 and 7 d.p.i. compared with 10 and 14 d.p.i.
Interleukin-10 and
interleukin-6 were up-regulated at 14 d.p.i. in the infected groups. This study expands our understanding of the dynamics of replication of
vaccine and virulent MDV strains in the feathers and illuminates mechanisms associated with immunity to
Marek's disease.