Marek’s disease control still a challenge for poultry industry
While not changing rapidly, the Marek’s disease virus is gradually evolving over time, which keeps it front and center as a serious health problem for the broiler and egg layer industries.
The development of the first Marek's disease vaccine in the late 1960's was a major accomplishment in the history of animal health, according to Dr. Isabel Gimeno, associate professor, College of Veterinary Medicine, North Carolina State University. She told the audience at the "Managing Marek's disease for your most valued birds" webinar, sponsored by Zoetis and presented by WATT Global Media on December 18, 2013, that the original Marek's vaccine was the first successful vaccine for a tumor-causing disease.
Gimeno, whose primary research interest is Marek's disease, said that the Marek's disease virus has evolved over time, and it will continue to present a challenge for poultry producers. She said that the original HVT vaccine for Marek's disease was effective from its introduction in 1969 until the 1980s, when it was replaced with bivalent vaccines, which were replaced themselves in the 1990s with the Rispens vaccines. The Maerek's disease viruses in the field continue to evolve and become more virulent, she said.
Management and correct use of vaccines are critical for protecting against the Marek's disease virus, according to Gimeno. She said that in ovo vaccination provides better protection against the Marek's virus for the bird than does subcutaneous vaccination. For farms that have a severe Marek's challenge, she recommended in ovo vaccination with HVT followed by day-of-age vaccination with a Rispens vaccine. She cautioned that, in all cases, it is important to administer the full dose of vaccine to all birds.
High challenge situations
Dr. Kalen Cookson, director of clinical research, Zoetis, said that Marek's disease related mortality is just the "tip of the iceberg" when evaluating the true cost of the disease. He said that the immune suppression that non-fatal Marek's infections can cause is a major threat for flocks.
Cookson said that on farms with a strong Marek's disease virus challenge from a particularly virulent strain, using a Rispens vaccine gives significantly better protection than do conventional bivalent vaccines in both broilers and breeders and table egg layers. He said that Low-passaged "European" Rispens CVI-988 gives the greatest margin of efficacy in high challenge situations.