Cause

The disease is caused by an avian adenovirus (strain BC14, virus 127), the EDS virus does not belong to any of the 12 fowl adenoviruses.

Transmission

The virus is transmitted through the egg to a few birds in a flock. These birds carry the virus until the flock comes into lay at which time they begin to excrete virus and infect birds kept in the same house. Horizontal spread through infected litter can and does occur once a flock shows the disease. It seems however that the virus is not very infectious or the level of virus excretion is low.

Species affected

Only chickens are susceptible to clinical disease due to EDS virus. However, the virus is widespread in ducks but does not cause any problems.

Clinical signs

EDS affects only layers and breeders at the start of or during their egg production. Affected flocks show a failure to reach peak egg production or a drop in egg production accompanied by an inferior eggshell quality. In the case of brown eggs, a loss of shell color. Affected birds may also appear to be anaemic, may show a transient diarrhoea and sometimes the feed intake may be reduced. No increased mortality or other symptoms are observed. No specific internal lesions can be noted.

Diagnosis

Clinical signs provide the diagnosis for EDS. Virus isolation and antibody tests can confirm this.

Differential diagnosis

Infectious bronchitis and to a lesser extent Newcastle disease and infectious laryngotracheitis will have to be considered. Proper diagnostic tests such as the antibody tests will eliminate doubt.

Treatment and control

There is no treatment against egg drop syndrome. Vaccination with an inactivated vaccine before point of lay is the only available, effective method for the control of EDS.