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United States Department of Agriculture

Agricultural Research Service

Healthy Animals Newsletter

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Issue 17, January 2004
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ARS Keeps Up Fight Against Marek's Disease

Marek's disease is a naturally occurring, cancer-like disease that can lead to death or production losses in chickens. It is generated by a herpesvirus that suppresses the immune system and causes abnormal cell growth in nerves and tumors in the major internal organs. ARS scientists are at the forefront of efforts to wipe out this costly disease of commercial layers and broilers.

Retired ARS scientist Richard Witter and his colleagues at the ARS Avian Disease and Oncology Laboratory (ADOL) in East Lansing, MI, first discovered in the 1960s the herpesvirus that causes Marek's disease, and were the first to develop a vaccine in 1970.

Although there are now several vaccines that have substantially reduced losses, they are not 100 percent effective. New and more pathogenic viral strains are continually emerging.

Once a chicken is infected with Marek's disease, it will most likely die. Young chickens are most susceptible, but older, unvaccinated birds develop the disease, too. Hens do not pass the disease to their offspring through their eggs. The virus is shed from feather follicles. Chickens become infected when they inhale the virus through dander in their environment. Economic losses are estimated to be about $160 million a year in the United States.

ChickensIn 2000, ARS scientist Lucy Lee and her colleagues at ADOL sequenced the genetic code of the virus that causes the disease (see AR magazine story). With this genetic code, they are now studying the molecular mechanisms by which it causes the disease and hope to create new vaccines. Another ARS team in New York sequenced another strain, as well as a harmless variant in turkeys that is used to vaccinate chickens.

ARS researchers have different approaches in several disciplines to combine their strengths and gain a better understanding of how the virus interacts with its host. They are inoculating test chickens with genetically altered viruses to see if they will either cause disease symptoms or stimulate a response in the immune system. Armed with this information, they are designing recombinant vaccines that protect against very virulent strains.

Besides new vaccines, breeders must also follow proper management and hygiene procedures and have resistant stocks to prevent Marek's disease. That's why ADOL researchers are developing inbred chicken lines with disease-resistant traits linked to one or more genes, which helps them isolate and identify genes with disease resistance. They want to identify genes, proteins and biological pathways associated with immune responses. They've identified several Marek's-disease-resistant genes and immunological responses that confer resistance.

In related work, ARS Geneticist Hans H. Cheng and other ADOL researchers are part of an international team mapping the chicken genome. A complete map (anticipated for early 2004) would provide researchers the tool to develop chickens with resistance to diseases, and Marek's is the first one targeted.

For more information, contact:

Aly M. Fadly, East Lansing, MI

Research Briefs

ARS has teamed-up with Purdue University to find more humane methods of rearing poultry used in food production systems.
Heng-Wei Cheng
(765) 494-8022

An ARS researcher and a Mississippi State University researcher received a grant to further study a method they developed to track pathogen infections in live pigs.
Donald C. Lay
(765) 496-7750

Ground was recently broken on an expansion and upgrade of an ARS forage and livestock research facility in Oklahoma.
Phillip Sims
(580) 256-7449

ARS researchers are studying how stable flies have moved from being pests mainly on cattle in the barnyard to become problems in pastures and rangeland areas as well.
Phil Scholl
(402) 437-5267

A new approach to experimental vaccines has been developed by ARS scientists against exotic Newcastle disease in poultry.
Darrell Kapczynski
(706) 546-3471

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About This Newsletter

ARS Animal Health Research Laboratories

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Last Modified: 2/6/2007
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