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Characterisation of two highly oncogenic strains of Marek's disease virus
K A Schat1, B W Calnek, J Fabricant
1Department of Avian and Aquatic Animal Medicine, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA.
Abstract:
The RB-1B and ALA-8 strains of Marek's disease (MD) virus, which were isolated from chickens with MD and which had been vaccinated with the herpesvirus of turkeys (HVT), were evaluated for their oncogenic potential in genetically susceptible (P-line) and resistant (N-line, PDRC) chickens. RB-1B and ALA-8 were both highly oncogenic, causing a high incidence of MD in both susceptible and resistant birds. Vaccination of P-line birds with SB-1 or HVT did not protect satisfactorily against RB-1B. However, a bivalent vaccine consisting of SB-1 and HVT enhanced protection significantly. HVT alone, and the bivalent vaccine, protected PDRC and N-line chickens well against RB-1B, but SB-1 was less protective in PDRC birds. HVT protected equally well against challenge with ALA-8 and the standard JM-10 strain. Differences in the pathogenesis of viral infection could not be detected among ALA-8, RB-1B and JM-10 between 4-7 days post-infection (d.p.i.). However, after d.p.i. 12 RB-1B caused significantly higher levels of viral internal antigen and virus isolation rates than did JM-10 in the same genetic strain. Prior vaccination prevented the expression of ALA-8 at 5 and 20 d.p.i., but not that of RB-1B. Pathogenetic events such as expression of VIA or level of virus infection appeared to be directly related to the level of protection observed in challenged birds.
Insights
New Marek
Area of Science:
- Veterinary Virology
- Poultry Immunology
- Oncology
Background:
- Marek's disease (MD) poses a significant threat to poultry health and industry.
- Understanding the oncogenic potential of different MD virus (MDV) strains is crucial for effective vaccination strategies.
- Genetic resistance and susceptibility in chickens influence disease outcomes and vaccine efficacy.
Purpose of the Study:
- To evaluate the oncogenic potential of RB-1B and ALA-8 MDV strains.
- To assess the efficacy of different vaccines (HVT, SB-1, bivalent) against these strains in genetically diverse chickens.
- To investigate the pathogenesis and viral shedding differences between MDV strains.
Main Methods:
- Infection of genetically susceptible (P-line) and resistant (N-line, PDRC) chickens with RB-1B and ALA-8 MDV strains.
- Vaccination of chickens with HVT, SB-1, or a bivalent SB-1/HVT vaccine prior to challenge.
- Monitoring of disease incidence, viral antigen expression, and virus isolation rates post-infection.
Main Results:
- RB-1B and ALA-8 demonstrated high oncogenicity in both susceptible and resistant chicken lines.
- A bivalent SB-1/HVT vaccine provided significantly enhanced protection against RB-1B compared to monovalent vaccines.
- RB-1B showed higher viral antigen expression and isolation rates after 12 days post-infection compared to JM-10.
Conclusions:
- RB-1B and ALA-8 are highly virulent MDV strains requiring robust vaccination approaches.
- Bivalent vaccination strategies offer superior protection against virulent MDV strains like RB-1B.
- Pathogenesis, including viral internal antigen expression and shedding, correlates with observed protection levels.
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