Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2002
Publication Date: 10/1/2002
Citation: Gimeno, I.M., Witter, R.L., Neumann, U. 2002. Neuropathotyping: a new system to classify marek's disease virus. Avian Diseases. 46:909-918. Interpretive Summary: Marek's disease (MD), a virus-induced cancer-like disease of chickens, is considered as a major disease problem in commercial poultry. Vaccination has dramatically reduced the incidence of the disease, but very little is known about the factors of virulence of the virus and therefore about ways to classify viruses according to their pathogenicity. The objective of this research was to establish an easy method for classify MDV strains according to their neurovirulence. We have determined that neurovirulence is a good criterion for evaluating MDV pathogenesis and thereby for classifying MDV strains in neuropathotypes. This important information about neuropathotyping will help scientists in academia and industry understand the biology of the more virulent strains of MDV and eventually lead to better control of the disease.
Technical Abstract: An statistical approach was used to establish a new classification system of Marek's disease virus (MDV) based on neurological responses. To develop the system, neurological response data from 15x7 chickens inoculated with 30 strains of serotype 1 MDV were statistically analyzed by a cluster analysis. The goal was to identify a statistical system that would verify if three neurovirulence groups correlated with the three pathotypes previously described. The system was also validated in two additional strains of SPF chickens, SPAFAS, and line SC (Hy-Vac). The proposed system is based on analysis of three variables: (1) frequency of birds showing transient paralysis between 9 and 11 days post inoculation (dpi), (2) mortality before 15 dpi, and (3) frequency of birds showing persistent neurological disease between 21 and 23 dpi. By use of this system, a MDV may be classified in one of three groups, designated neuropathotype A, B and C, which roughly correspond to the virulent (v), very virulent (vv) and very virulent plus (vv+) pathotypes, respectively. However, correlation between neuropathotype and pathotype was not absolute, and neuropathotyping is more a complement to the current pathotyping system than a replacement for it. Our results showed that neuropathotyping studies can be conducted in two types of commercial SPF chickens by the use of the same variables, although the system would first have to be standardized by the use of prototype viruses. Neuropathotypes can also be estimated without statistical analysis with reasonable accuracy. By use of this analysis, we established that MDV strains within the vv pathotype may be subdivided into neuropathotypes B and C, thus establishing a previously unrecognized pathotypic classification. This finding illustrates how neuropathotyping may extend important information not identified by conventional pathotyping.