Isolation of chicken anaemia agent and Marek's disease virus from chickens vaccinated with turkey herpesvirus and lesions induced in chicks by inoculating both agents.

A disease that was characterised by high mortality, necrotic lesions, severe thymic and bursal atrophy, as well as Marek's disease (MD) lesions, occurred in two young layer chicken flocks vaccinated with turkey herpesvirus (HVT) at hatching. An agent similar to the chicken anaemia agent, designated CAA82-2, and a virulent MD virus strain, designated Md82-2, were isolated from the kidneys of affected chickens. Dual inoculation of young chicks with both agents resulted in early mortality associated with severe necrosis and depletion of lymphocytes in the lymphoid organs and aplasia of the bone marrow. The similarity of this disease induced in chicks to an early mortality syndrome caused by variant MD virus strains was discussed.