Marek's disease in genetically susceptible Cochin chickens in Italy: a case report

The present study investigates an outbreak of classical Marek's disease (MD) in backyard Cochin chickens reared for hobby in Italy. Examined chickens showed spastic paralysis of the legs and at necropsy, enlargement and discoloration of the peripheral nerves and plexuses that matched microscopic A‑ and B‑ type MD lesions. Molecular analysis of the meq gene of the detected Gallid alphaherpesvirus 2 (GaHV‑2) strain, showed typical markers of low virulence and the strain shared the entire meq gene sequence with strains circulating in Italian backyard chickens. Furthermore, the haplotype B19 of the major histocompatibility complex (MHC) was defined in the affected chickens, showing that the birds possessed a genetic profile of high susceptibility to MD, allowing the appearance of a classical nervous clinical form after infection with an apparently low pathogenicity GaHV‑2 strain. Trade of live ornamental purebred chickens occurs frequently between hobby farmers and biosecurity practices, such as quarantine periods, should be applied to avoid the introduction of infected animals. Veterinarians should raise awareness of this issue and promote the use of vaccines against MD.