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The Mut UL5-I682R Marek's disease virus with a single nucleotide mutation within the helicase-primase subunit gene not only reduces virulence but also provides partial vaccinal protection against Marek's disease

Hildebrandt, Evin, Cheng, Hans H.
Avian diseases 2015 v.59 no.1 pp. 94-97
chickens, sequence analysis, neoplasms, Meleagrid alphaherpesvirus 1, evolution, immunosuppression, turkeys, nerve tissue, vaccine development, genes, viruses, recombinant vaccines, death, Marek disease, virulence, point mutation, disease incidence
Marek’s disease virus (MDV) is an oncogenic herpesvirus that afflicts chickens with the disease known as Marek’s disease (MD). This virus induces tumors, nerve lesions, immunosuppression, and death of affected birds. Vaccines are the primary control method for MD but, due to the periodic evolution of field strains, it is necessary to explore the development of new MD vaccines. MD vaccines are often attenuated MDV strains generated through serial passage in vitro. We previously used experimental evolution of MDV to provide a better understanding of the genetic basis of attenuation. During complete genome sequencing of evolved MDV populations, we identified a point mutation within the UL5 helicase-primase gene and created a UL5 recombinant virus that significantly reduced disease incidence by 89%–100%. To determine if experimental evolution also identifies mutations that provide protective qualities as potential vaccine candidates, we tested the UL5 recombinant virus as a vaccine and compared its protection to commercial herpesvirus of turkey (HVT) and bivalent (HVT + SB-1) vaccines. Both commercial vaccines resulted in higher protection against MD than did the UL5 recombinant virus, although the UL5 virus did provide protection against developing MD in 46%–70% of birds challenged. This indicates that a mutation within the UL5 helicase-primase gene not only reduces virulence but also confers protection against challenge with virulent MDV, providing support that not only can experimental evolution identify candidate mutations involved in attenuation but can also identify potential candidates for use in vaccine development.