Egg drop syndrome-76 (EDS-76)
An outbreak of sudden drop in egg production or a failure to achieve a normal peak in production despite optimum managemental and nutrition status is attributed to a viral disease called as EDS-76. The cause was identified as adenovirus, first isolated in Northern Ireland in 1976. Mortality is usually negligible. Circumstantial evidence suggests that the main route of transmission is through the eggs (vertical transmission) followed by latent infection during growing stage with viral excretion starting shortly before sexual maturity. Contamination of egg trays at packing stations and biting insects may play a part in transmission. The virus is commonly present in ducks and geese but does not cause the disease. Lateral transmission from bird to bird is slow.
Symptoms and lesions: The disease occurs during sexual maturity. Birds do not show clinical signs of the disease except drop in egg production at peak or failure to peak. Drops may be up to 50% and for 3-4 weeks duration. Rough, thin or soft-shelled eggs and shell-less eggs, loss of shell pigment, poor internal quality are the other indications.
Diagnosis: Diagnosis is made from the characteristic clinical feature of rapid drop in egg production during the peak production in broiler parents, the characteristic shape of the eggs laid and the virus isolation from the cloacal swabs. EDS-76 virus can agglutinate red cells of chicken, duck, turkeys, geese and pigeons but not mammalian cells. The virus can be propagated in 9 day embryonated duck eggs by the allantoic route in which it produces very high titre. The antibody in affected flock can be detected either by hemagglutination inhibition, virus neutralization or ELISA tests.
Prevention and control: Vertical transmission can be avoided by selection of birds from uninfected flocks and good hygiene and management. Proper disposal of infected eggs should be made as they are the most important source of the virus. Vaccination with an oil adjuvant inactivated vaccine is reported to give good protection when given at 14 to 16 weeks of age.