Marek's disease virus
Marek's disease virus (MDV), also referred to as Gallid herpesvirus 2 (GaHV-2), is a highly cell-associated lymphotropic alpha-herpesvirus that causes Marek's disease (MD) in domestic chicken worldwide.
Although there is a vaccine against MDV, there has been increased virulence frequently isolated in some countries, even among vaccinated chickens.
The virus is spread in dander from the birds' feather follicles and transmitted to other birds which inhale or ingest the virons. MDV can remain in the environment for months to years.