Prevention of Marek's disease using a filtered air positive pressure house

A facility for keeping chickens free of Marek's disease (MD) was obtained by adopting a system of filtered air under positive pressure (FAPP) for ventilation, and by imposing restrictions on entrance of articles, materials and personnel. During 741 days of the FAPP operation, there has been no evidence of infection with MD virus even though MD was enzootic in flocks housed on the same farm.