Submitted to: International Marek's Disease Symposium Abstracts and Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/14/2004
Publication Date: 7/14/2004
Citation: Witter, R.L., Calnek, B.W., Buscaglia, C., Gimeno, I.M., Schat, K.A. 2004. Towards a universal pathotyping methodology for Marek's disease virus [abstract]. International Marek's Disease Symposium Abstracts and Proceedings. Paper No. III-5. Interpretive Summary:
Technical Abstract: The concept of pathotype in Marek's disease (MD) dates the recognition of a more virulent form of the disease in the late 1950s. Distinctions between MD viral strains were further expanded with the description of the vv pathotype in the early 1980s and of the vv+ pathotype in the 1990s. These pathotype designations reflect important biological properties that correlate with the break-through of vaccinal immunity in the field. However, pathotyping methods applied by various laboratories have not been uniform, preventing critical comparison of results. Better uniformity of pathotyping procedures is urgently needed. The ADOL method is based on the induction of lymphoproliferative lesions in vaccinated chickens. This method has been used to pathotype more than 45 isolates and is the basis for the current pathotype classification of MDV strains. Its limitations include requirements for a specific type of chickens (15x7 ab+), large numbers of animals, and a statistical method to compare lesion responses to those of JM/102W and Md5 control strains. Because of these limitations, it is not likely to be used in other laboratories. We suggest that comparability in pathotyping could be improved by the comparison of field isolates to standard prototype strains such as JM/102W, Md5 and 648A (American Type Culture Collection) or their equivalents. Pathotype would be assigned based on a 'best fit' of the data to that of the prototypes. Data may be generated by several alternative procedures that utilize tumor induction, a mixture of tumor induction and nonneoplastic lesions neuropathotyping), or other nonneoplastic criteria (lymphoid organ weights, virus replication). Methods based on neoplastic criteria, especially when generated in MD-immunized chickens, will likely correlate most closely with that of the ADOL method and be most relevant to evolution of MD virus in the field. A modification of the ADOL method that utilizes fewer chickens of commercial SPF strains is proposed and, based on limited comparative data, is expected to provide generally comparable results. However, a variety of other criteria (see above) can also be utilized both for primary pathotyping and as adjuncts to other pathotyping methods. Advantages and disadvantages of alternative methods will be presented.