Translator Disclaimer
11 June 2014 Molecular Evolution of Marek's Disease Virus (MDV) Field Strains in a 40-Year Time Period
Grzegorz Woźniakowski, Elżbieta Samorek-Salamonowicz
Author Affiliations +
Abstract

Marek's disease (MD) presents a serious threat in poultry production. The disease has been limited for over 40 yr by protective vaccination. The widely applied vaccination against MD is also one of the factors causing evolutionary pressure onto field Marek's disease virus (MDV) virulent strains. Molecular evolution of MDV genes involved in oncogenesis may increase the pathogenicity of MDV virulent strains. The goal of the presented study was to sum up the molecular evolution of MDV field strains isolated in the last 40 yr in Poland. In total, 85 field MDV strains collected between 1974 and 2012 were propagated in chicken embryo fibroblasts. After DNA extraction, three sets of primers were designed for PCR complementary to the MDV076 (RLORF7) region encoding the meq oncogene as well to the MDV077 (23 kDa protein binding alpha-enolase) and MDV077.5 (RLORF6) genes. The obtained 85 MDV076, 60 MDV077, and 58 MDV077.5 cloned fragments were sequenced and aligned with the sequences of reference MDV strains showing different pathogenicity levels. The retrieved nucleotide (nt) and deduced amino acid sequences of RLORF7, 23 kDa protein, and LORF6 of Polish field strains showed several mutations and substitutions homologous to those observed in reference strains with a determined pathogenicity. The observed changes indicated the continuous evolution of field MDV strains. The RLORF7 nt sequence of analyzed MDV isolates showed similarity to virulent and very virulent MDV reference strains. The obtained 23 kDa and LORF6 nt sequences provided more important data and were more similar to mildly pathogenic strains than to virulent and very virulent MDV. The specific nt motifs in all three genes may indicate an increase of MDV virulence and were found in strains starting from 2006. According to the obtained results, the strains isolated in 2012 are similar to the very virulent plus MDV group. The study showed that RLORF7, 23 kDa protein, and RLORF6 fragments harbor sequence motifs that may have some association with MDV pathogenicity level. However, the exact role of the investigated regions in pathogenicity should be further examined by knock-out MDV strains. Also, the true MDV pathotype may only be determined by traditional in vivo experiments.

Evolución molecular de cepas de campo del virus de la enfermedad de Marek (MDV) en un período de 40 años.

La enfermedad de Marek (MD) presenta una seria amenaza para la producción avícola. La enfermedad ha sido limitada durante más de 40 años por la protección inducida por la vacunación. La vacuna ampliamente aplicada contra la enfermedad de Marek es también uno de los factores causantes de la presión evolutiva sobre las cepas virulentas del virus de la enfermedad de Marek. La evolución molecular de los genes implicados en la oncogénesis del virus de Marek puede aumentar la patogenicidad de cepas virulentas. El objetivo del estudio presentado fue resumir la evolución molecular de cepas de campo del virus de Marek aisladas en los últimos 40 años en Polonia. En total, 85 cepas de campo recolectadas entre 1974 y 2012 se propagaron en fibroblastos de embrión de pollo. Después de la extracción de ADN, se diseñaron tres conjuntos de iniciadores para llevar a cabo un método de PCR complementario a las regiones MDV076 (RLORF7) que codifica para el oncogene meq y también para los genes MDV077 (proteína de unión alfa-enolasa de 23 kDa) y para el gene MDV077.5 (RLORF6). Los fragmentos clonados obtenidos, 85 para el gene MDV076, 60 para el gene MDV077 y 58 para el gene MDV077.5, fueron secuenciados y se alinearon con secuencias de referencia del virus de la enfermedad de Marek que muestran diferentes niveles de patogenicidad. Las secuencias de nucleótidos y de aminoácidos deducidos de RLORF7, de la proteína de 23 kDa y LORF6 de cepas de campo polacas mostraron varias mutaciones y sustituciones homólogas a los observados en las cepas

American Association of Avian Pathologists
Grzegorz Woźniakowski and Elżbieta Samorek-Salamonowicz "Molecular Evolution of Marek's Disease Virus (MDV) Field Strains in a 40-Year Time Period," Avian Diseases 58(4), 550-557, (11 June 2014). https://doi.org/10.1637/10812-030614-Reg.1
Received: 11 March 2014; Accepted: 1 June 2014; Published: 11 June 2014
JOURNAL ARTICLE
8 PAGES


Share
SHARE
RIGHTS & PERMISSIONS
Get copyright permission
Back to Top