Systematic Veterinary Virology

TRANSMISSION

• The virus is transmitted through the egg (vertically) to a few birds in a flock, these birds carry the virus (as latent infection) until the flock comes into lay at which time they begin to excrete virus and infect birds kept in the same house.
• The virus is shed in the faeces and spread can be by contaminated water and fomites. Sporadic outbreaks have also been attributed to wild birds contaminating water. Horizontal spread occur through infected litter. Man and contaminated fomites such as crates or trucks can spread virus, which also can be transmitted by needles when vaccinating and drawing blood.
• Insect transmission is possible but not proved.  After horizontal or experimental infection, the virus grows to low titers in the nasal mucosa. This is followed by viremia, virus replication in lymphoid tissue, and then massive replication for ~8 days in the oviduct, especially in the pouch shell gland region.
• Changes in the eggshell occur coincidentally. Both the exterior and interior of eggs produced between 8 and ~18 days after infection contain virus. A copious exudate in the lumen of the oviduct is rich in virus, and this contaminates the droppings.