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Scientists Crack Code of Virus That Causes Key Chicken Disease

In a step towards creating new chicken vaccines, Agricultural Research Servicescientists have cracked the biochemical code of the herpesvirus that causes Marek’s disease.

Severe cases of Marek’s can cause cancerlike tumors, partial paralysis and other disorders in afflicted birds. Although vaccines made from benign or disabled Marek’s strains are commercially available, some are failing to immunize the birds against virulent new forms of the virus that have emerged. Bird deaths, diminished egg laying and carcass condemnation costs at processing plants due to Marek’s cause an estimated $1 billion annually worldwide, and up to $100 million in the United States alone.

In recently published studies, ARS researchers led an effort to chart the nucleotide sequences for two Marek’s disease strains--MDV1-Md5 vv and MDV1-GA--and a non- disease-causing variant in turkeys called serotype 3, which is used to vaccinate chickens. Nucleotides are chemical subunits whose arrangement spells out the DNA alphabet for the virus’s 100-plus genes.

Now available on the GenBank database, Marek’s nucleotide coding will help speed the identification of viral genes and mechanisms by which the pathogen survives in nature, evades a host’s immune system and causes disease, according to Sanjay Reddy, a medical safety officer at ARS’ Avian Disease and Oncology Laboratory, East Lansing, Mich.

There, Reddy and colleagues Lucy Lee, Robert Silva and Richard Witter are using information gleaned from Marek’s nucleotide coding to study the genes it uses to produce tumors in chickens, as well as silence them. They’ve also begun using gene- splicing techniques to design recombinant vaccines to better protect chickens from GA and Md5 vv, as well as other virulent Marek’s disease strains.

Both are tumor-causing members of a herpesvirus family that researchers around the world have been studying for more than 20 years and--until now--only partially decoded, notes Lee, a research chemist.

A more detailed story about the work appears in this month’s issue of Agricultural Researchmagazine.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.