Using Comparative Genomics to Manage Marek's
December 6, 2006
The genetic code for a virulent
strain of Marek's disease virus was cracked a few years ago. Now, to determine
how best to cripple it and other infectious strains, Agricultural Research
Service (ARS) scientists are working to
decipher the genomes of several nonvirulent Marek's disease (MDV) vaccine
Spatz at the ARS
Poultry Research Laboratory in Athens, Ga., and
Silva at the ARS
Disease and Oncology Laboratory in East Lansing, Mich., have teamed up to
compare nonvirulent MDV strains used in vaccines.
Marek's disease is the first cancer-causing virus for which a
tumor-preventing vaccine was developed. In the United States, 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 programs, 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 program. 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
ARS is the U.S. Department of
Agriculture's principal scientific research agency.