Early Changes in Bursa of Fabricius from Marek's Disease

SUMMARY Seventy Line 7 X specific-pathogen-free (SPF) hybrids were inoculated with four isolates of the Marek's disease (MD) agent. The strains used were the JM and Conn-A agents, chosen as standard isolates, and materials from two field outbreaks. Whole blood from infected donors was the source of inoculum; both undiluted and phosphate-buffered saline dilutions of blood were inoculated. At 12 days postinoculation, bursas were dramatically smaller in all chicks receiving undiluted blood, and less small in those receiving dilutions of blood. Histologic evaluation revealed changes in the bursa reported by others as typical for MD infection, plus other lesions associated with early MD infection.