Managing Marek's disease through genomics
Scientists at the Agricultural Research Service (ARS)
are working to decipher the genomes of several nonvirulent Marek's disease (MDV)
vaccine strains, in order to identify how to best fight virulent and other
infectious strains of the disease.
is the first cancer-causing virus for which a tumour-preventing
vaccine was developed. In the US, most commercial chickens are vaccinated
against Marek's disease virus type 1 (MDV1) while inside the egg. In Europe,
chicks are vaccinated when they are one day old. While these very successful
vaccination programmes, begun in the 1960s, have saved the industry billions of
dollars, the MDV problem still persists.
That's because selective pressures imposed on the virus in vaccinated birds
cause new variants to evolve that could pose a threat to the poultry industry.
Because the virus is constantly evolving, new vaccines have to be developed to
keep them in check.
To investigate the differences between the variants, Spatz and Silva
initiated a comparative genomics research programme. It involves determining the
DNA sequences of various strains of MDV. Some of these are nonvirulent ones used
as commercial vaccines, while others cause severe disease in chickens. By
examining the differences between these strains at the DNA level, the two
researchers hope to identify the genes involved in virulence - that is, the
virus' ability to cause disease.
Once these genes have been identified, improved vaccines containing
modifications in the virulence genes can be engineered and used to protect
chickens against current disease-causing MDV strains, as well as against future
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