Molecular characterization of Marek’s disease virus detected in backyard chickens affected by classical nervous form

An outbreak of Marek’s disease nervous form in unvaccinated Cochin chickens from an Italian backyard flock is reported. After suppression two birds, showing inability to stand upright and spastic paralysis of legs, were necropsied and organs were taken for histologic examination and molecular analysis. MDV-1 was detected from feathers by PCR targeting meq gene.meq gene of the detected strain was fully sequenced along with commercial vaccines most commonly used in Italy. Nucleotide and amino acid sequences were compared to selected MDV-1 reference strains with different degrees of pathogenicity, retrieved from GenBank. The sequence analysis and the high number of PPPP repeats found in the transactivation domain of the Meq protein showed that the detected virus was closely related to mild or attenuated MDV-1 strains, but different from the analyzed vaccines. The molecular results were supported by clinical, macroscopic and microscopic findings. A- and B-type lesions, highly suggestive of a mild MDV-1 infection, were observed in peripheral nerves.MHC haplotype B19, known to be correlated with high susceptibility to Marek’s disease, was found in affected chickens by PCR and sequencing of B-LβII family genes. Because sequencing of the meq gene is not a sufficient criteria in determining the pathotype, virus isolation will be attempted in order to confirm the molecular results by in vivo experimental trials.