Egg drop syndrome.

Egg drop syndrome '76 is a viral disease that can cause significant economic losses in poultry. The causative virus, duck atadenovirus A, is widespread among asymptomatic waterfowl. Outbreaks of respiratory disease, with elevated mortality, have been reported rarely in ducklings and goslings. However, the most significant impact of this virus is on the chicken industry. Egg drop syndrome '76 was first described in chickens in the 1970s. The initial outbreaks were linked to a contaminated Marek’s disease vaccine, which infected breeding chicken flocks. The virus subsequently spread to other flocks through infected eggs. In chickens, duck atadenovirus A causes egg production to fall, and many eggs are thin-shelled, shellless or otherwise abnormal. Although the initial outbreaks were controlled by eradicating this virus from commercial breeders, it became endemic in chickens in some parts of the world. Viruses carried in ducks and geese can also spread to chickens, either during direct contact or through sources such as contaminated water. A few outbreaks, with clinical signs similar to those in chickens, have been reported in quail and turkeys, and this syndrome might also occur in other birds.