Mareks Disease

Caused by a herpesvirus

Hosts

• The most important disease of unvaccinated backyard chicken flocks

Pathogenesis

• Replicates initially in the lungs and B cells
• Enters feather follicles: produces virus-laden dander that is shed into litter
• Reaches T cells, causing proliferation without virus protein production
• T cells localize in brain or nerves causing encephalitis
• End stage: massive visceral tumors

Epidemiology

• More virulent strains evolving: presents a challenge to vaccinal immunity

Control

• Removal of litter between batches of chicks
• Vaccines administered in ovo at 18 days