title: Characterizing in vivo stability and potential interactions of a UL5 helicase-primase mutation previously shown to reduce virulence and in vivo replication of Marek's disease virus.
abstract: The unpredictable yet recurrent emergence of more virulent field strains of Marek's disease virus (MDV) in Marek's disease (MD) vaccinated flocks of chickens has prompted concerns regarding the sustainability of MD vaccines. A single non-synonymous point mutation (I682R) within the UL5 helicase-primase unit was shown to reduce virulence by over 90%. Considering in vitro attenuation is commonly used to generate MD vaccines, this result prompted further characterization of this mutation, particularly to better understand the potential of point mutations for use in vaccine development. Incorporation of a second non-synonymous point mutation (UL46-Q117R; tegument) found at high frequencies in the same attenuated MDV as the UL5 mutation did not further reduce virulence compared to the single UL5 mutation alone. Furthermore, when the UL5-containing MDV was serially passed three times in vivo, the resulting viruses did not show increases in replication or virulence, and no revertant viruses could be detected. This suggests that point mutations that reduce fitness and in vivo replication may be more stable than initially anticipated, which may alleviate some concerns regarding rationally designed MD vaccines based upon point mutations.
authors.affiliation: Genetics Program, Michigan State University, East Lansing, MI 48824, United States; USDA, ARS, Avian Disease and Oncology Laboratory, East Lansing, MI 48823, United States.
authors.forename: Evin
authors.initials: E
authors.lastname: Hildebrandt
authors.affiliation: USDA, ARS, Avian Disease and Oncology Laboratory, East Lansing, MI 48823, United States.
authors.forename: John R
authors.initials: JR
authors.lastname: Dunn
authors.affiliation: USDA, ARS, Avian Disease and Oncology Laboratory, East Lansing, MI 48823, United States. Electronic address: hans.cheng@ars.usda.gov.
authors.forename: Hans H
authors.initials: HH
authors.lastname: Cheng
mesh_terms: D000818:Animals; D002645:Chickens; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D019915:DNA Primase / Q000235:genetics / Q000378:metabolism*; D042822:Genomic Instability; D008381:Herpesvirus 2, Gallid / Q000201:enzymology* / Q000235:genetics / Q000502:physiology*; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D012692:Serial Passage; D014613:Vaccines, Attenuated / Q000235:genetics / Q000302:isolation & purification; D014765:Viral Vaccines / Q000235:genetics* / Q000302:isolation & purification; D014774:Virulence; D014779:Virus Replication
chemical_list: D050505:Mutant Proteins; D014613:Vaccines, Attenuated; D014765:Viral Vaccines; D019915:DNA Primase; D004265:DNA Helicases
keywords: Attenuated; Marek's disease virus (MDV); Replication; UL5 helicase-primase subunit; Virulence