Atypical cells in the peripheral blood of chickens exposed to Marek's disease agent.

Atypical cells, containing opaque blue cytoplasmic globules when stained with Wright's or May-Grünwald-Giemsa stain, were observed in Gamefowl (GF-WSU) experimentally exposed by contact to a classical Marek's disease (MD) agent, and in White Leghorn chickens (RPL Line 7) in which group "spontaneous" cases of classical MD developed. Such cells were absent in uninfected control birds. The cells were most readily demonstrated in stained films of white blood cells of the peripheral blood after 24-hour culture in vitro. The atypical cells were present in the peripheral blood of chickens exposed to MD, but in numbers so few that the cells were rarely detected in direct blood smears.