December 8, 2006

USDA scientists to unravel Marek's disease genome to find vaccine

Scientists at the Agricultural Research Service (ARS) are working to decipher the genomes of several nonvirulent Marek's disease (MDV) vaccine strains, to identify ways to fight the disease.

Microbiologists Stephen Spatz at the ARS Southeast Poultry Research Laboratory and Robert Silva at the ARS Avian Disease and Oncology Laboratory have teamed up to compare nonvirulent MDV strains used in vaccines.

Marek's 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 have been very successful, the problem still persists.

Part of the reason is because selective pressures imposed on the virus in vaccinated birds cause new variants to evolve, which meant new vaccines have to be developed to keep up.

Researchers initiated a comparative genomics research programme which involves determining the DNA sequences of various strains of MDV. While some of these are nonvirulent ones used as commercial vaccines, 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.

Once identified, improved vaccines containing modifications in the virulence genes can be engineered and used to protect against current and future strains.