Systematic Veterinary Virology

TRANSMISSION

• The virus is highly infectious and, once it is present in a flock, it spreads rapidly to unvaccinated poultry. Healthy birds can be carriers and infect others. The virus can remain alive in the environment for as long as eight months.
• Virus replication and release occurs in the epithelial cells of feather follicles and copious amounts of infectious virus are shed in dust and dander. Susceptible birds are infected via the respiratory tract through contact with viral contaminated airborne dust particles. Three to five days post-infection B lymphocytes of the bursa of Fabricius, spleen and thymus become infected.
• The virus subsequently infects T lymphocytes of mostly the CD4+ phenotype; infection becomes latent and the virus spreads throughout the host by a cell-associated viremia. There is a secondary cytolytic infection of the feather follicle epithelium from which cell-free virus is produced and shed in feather dander and debris.
• Latently infected T lymphocytes are transformed leading to lesions of lymphomatosis in visceral organs. The main target cells for transformation are CD4+ T cells and probably CD8+ T cells. It is not spread from the hen to the chicken through the egg (No vertical transmission)