Evaluation of Marek's disease field isolates by the “best fit” pathotyping assay

Abstract

Although determination of the pathotype is central to the study of Marek's disease (MD) field isolates, methods are not standardized and results from different laboratories may not compare well with the original Avian Disease and Oncology Laboratory assay. This study was designed to investigate the validity of the "best fit" pathotyping assay, a simplified method recently described for testing of field isolates of MD virus (MDV). Twenty serotype 1 MDV strains were isolated from 12 breeder and commercial flocks in eight regions of the Russian Federation and were pathotyped by the best fit assay using vaccinated and non-vaccinated chickens from Schelkovo specific pathogen free breeders. Lesion responses induced by field isolates were compared with those induced by reference strains JM/102W, Md5, and 648A representing pathotypes v, vv and vv+, respectively. Based on comparison with reference strains, we determined the pathotype of eight isolates as vv+, 11 isolates as vv and one isolate as v. Lesion responses induced by the three reference strains consistently differentiated the respective pathotypes in non-vaccinated chickens and in chickens vaccinated with FC126 (serotype 3) alone or with a bivalent FC126 + 301B/1 vaccine (serotypes 3 and 2, respectively). Variation between reference strain responses in replicate trials was minimal. In some cases, calculation of the proportional distance between pairs of reference strains aided in the classification of field isolates. These results indicate that the "best fit" pathotyping assay can be conducted with local chicken strains and, in the absence of statistical analysis, provides pathotype designations that are consistent with those obtained by the Avian Disease and Oncology Laboratory method. In addition, the pathogenicity of Russian isolates appeared comparable with that of United States isolates.

Pathotyping of Australian isolates of Marek's disease virus and association of pathogenicity withmeqgene polymorphism

“…This, together with the lack of association between virulence and year of isolation in the present study, provides no evidence of a marked evolution in virulence of MDVs in Australia between the mid-1980s and mid-2000s. This contrasts with findings of very virulent plus strains in the USA (Witter et al, 1997), Korea (Sung, 2002), Argentina (Buscaglia et al, 2004) and Russia (Dudnikova et al, 2007).…”

“…Given these findings, the provisional virulence ranking of very virulent ascribed to this virus by De Laney et al (1998) cannot be supported. The issues associated with comparative pathotyping of strains of MDV in different countries using different methods have been well reviewed by Witter et al (2005), who concluded that the best approach is to use standard US prototype strains of known pathotype in pathotyping experiments as has been done in some recent studies (Dudnikova et al, 2007). This was not done in the present study, so results are assessed against earlier pathotyping methods such as the ADOL method of Witter (1997) and the neuropathotyping method of Gimeno et al (2002), in comparison also with earlier Australian pathotyping studies.…”

Sequence analysis of the Meq gene in the predominant Marek’s disease virus strains isolated in China during 2006–2008

“…strains [2]. In recent years, a number of very virulent or variant pathotypes of MDV have been isolated from various parts of the world [3][4][5][6][7][8]. Isolation and culture of MDV field strains is essential for monitoring changes in the predominant strains, and to evaluate the effectiveness of existing vaccines [9].…”

Virus de la Enfermedad de Marek: aproximación molecular al virus y respuesta inmune del hospedero

“…MEDICINA VETERINARIA Y ZOOTECNIA La virulencia se ha relacionado íntimamente con la clasificación patotípica, en la cual se designan cuatro tipos de virus relacionados como medio (mVEM), virulento (vVEM), muy virulento (vvVEM) y muy virulento plus (vv+VEM), actualmente se sospecha de la presencia de patotipos que exceden la virulencia de vv+VEM y se ha informado por lo menos de una de esas cepas, la 584A 2,18,32,36 .…”