Abstract
Marek’s disease virus (MDV) and reticuloendotheliosis virus (REV) cause Marek’s disease (MD) and reticuloendotheliosis (RE), respectively. Co-infection with MDV and REV is common in chickens, causing serious losses to the poultry industry. However, experimental studies of such co-infection are lacking. In this study, Chinese field strains of MDV (ZW/15) and REV (JLR1501) were used as challenge viruses to evaluate the pathogenicity of co-infection and the influence of MD vaccination in chickens. Compared to the MDV-challenged group, the mortality and tumor rates increased significantly by 20.0% (76.7 to 96.7%) and 26.7% (53.3 to 80.0%), in the co-challenged group, respectively. The protective index of the MD vaccines CVI988 and 814 decreased by 33.3 (80.0 to 47.7) and 13.3 (90.0 to 76.7), respectively. These results indicated that MDV and REV co-infection significantly increased disease severity and reduced the vaccine efficacy. The MDV genome load showed no difference in the feather pulps and spleen, and pathogenicity-related MDV gene expression (meq, pp38, vIL-8, and ICP4) in the spleen significantly increased at some time points in the co-challenged group. Clearly, synergistic pathogenicity occurred between MDV and REV, and the protective efficacy of existing MD vaccines was attenuated by co-infection with Chinese field MDV and REV strains.
Highlights
Marek’s disease virus (MDV) is an oncogenic alphaherpesvirus that causes Marek’s disease (MD), a major viral oncosis that affects poultry health worldwide [1]
Cytopathogenic effects (CPEs) in MDV ZW/15-infected chicken embryo fibroblasts (CEFs) were observed and confirmed by immunofluorescence assays (IFAs) using a MDV gE-specific monoclonal antibody (Figure S1A), and reticuloendotheliosis virus (REV) JLR1501 infection was determined by IFA using a REV gp90-specific monoclonal antibody (Figure S1B)
These results suggest that MDV and REV co-infection in specific pathogen-free (SPF) chickens significantly promoted the significantly promoted the expression of the pathogenicity-associated MDV genes at the mRNA level expression of the pathogenicity-associated MDV genes at the mRNA level at some time points during at some time points during the progression of viral infection
Summary
Marek’s disease virus (MDV) is an oncogenic alphaherpesvirus that causes Marek’s disease (MD), a major viral oncosis that affects poultry health worldwide [1]. Infection of chickens with virulent strains of MDV causes a serious group of severe symptoms, including T-cell lymphomas and solid visceral tumors, strong immunosuppression, and neurological disorders, leading directly to death or health complications in infected chickens [2,3]. Several MDV-encoded genes, including meq (MDV EcoRI-Q-encoded protein) [6,7,8], pp (MDV phosphoprotein 38) [9,10], vIL-8 (MDV-encoded CXC chemokine viral interleukin 8) [11,12], and ICP4 (MDV infected-cell peptide 4) [13,14,15], play important roles in MDV pathogenesis. The immune-protection mechanisms induced by MD vaccines are not fully understood currently, it is recognized that effective immunity to MD requires the involvement and coordinated activation of innate and adaptive immune responses [16]
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