Dual Infection of Chickens with Acute and Mild Strains of Marek's Disease Herpesvirus

SUMMARY Chickens became dually infected with acute and mild strains of Marek's disease herpesvirus (MDHV) within 3 to 4 weeks of exposure to litter contaminated with both strains of MDHV. Viremia due to the acute strain of MDHV (Id-l strain) alone was observed as early as the first week after exposure in the White Leghorn Cross (WSU-VS) and Gamefowl (GF-WSU) birds, but not until the second week in meat-type birds. Infection of birds with one strain of MDHV, whether acute or mild, did not prevent the subsequent infection by the other strain. The response of birds appeared different between different genetic lines of chickens even though exposed to the same contaminated environment.