Molecular epidemiology of Marek's disease virus in Italy in 2014-2016

Eighteen Marek’s disease virus (MDV-1) strains collected from clinical cases of Marek’s disease occurred from 2014 to 2016 in Italian commercial and backyard chicken flocks, were analyzed. Viruses were detected by a PCR protocol targeting the meq gene from feathers, spleen, liver or tumor samples of birds affected by classical nervous or acute forms. Nucleotide and amino acid sequences obtained, were edited and assembled using BioEdit software, then, using Clustal W, were aligned against and compared with complete homologous sequences of selected MDV-1 strains with different degrees of pathogenicity retrieved from GenBank. Phylogenetic analysis of meq genes was performed using neighbor-joining method including sequences of major vaccine strains currently used in Italy. Eight out of ten strains from vaccinated commercial chickens and two from unvaccinated backyard flocks, affected all by acute form, clustered together and with published Polish strains isolated in the last decade. Their sequences may be ascribed to virulent and very virulent MDVs. Six out of eight strains from unvaccinated backyard chickens with classical form were, as expected, closely related to mild and attenuated ones. Sequences of two strains from vaccinated white layer pullets with a clinical nervous form were instead very close to the sequence of a commercial vaccine. Peripheral neuropathy was suspected. In conclusion high virulence MDVs seems to circulate mostly in Italian commercial compartment where vaccination is routinely applied, while the rural sector is still affected by mild viruses probably due to the absent or lower vaccine pressure.