Egg drop syndrome (EDS) is caused by a hemagglutinating adenovirus infection in laying hens. It is characterised by the production of soft-shelled and shell-less eggs in apparently healthy birds. Birds tend to eat the shell-less eggs, which therefore may be missed unless a search is made for the membranes.
Incidences of diarrhoea and dullness and a loss in egg yolk pigmentation may occur before the eggshell changes, however mortality from Egg Drop Syndrome is usually negligible. The natural hosts for the Egg Drop Syndrome virus are ducks and geese, which are asymptomatic (do not show symptoms) carriers. Chickens of all ages and breeds are susceptible, however the disease is most severe in broiler breeders and brown-egg layer strains. Egg Drop Syndrome was first introduced into chickens through contaminated vaccine and spread through breeder flocks. It was first described in chickens in the 1970s and was spread all over the world except to the United States and Canada. Egg Drop Syndrome is a notifiable disease in most states of Australia.
Egg Drop Syndrome can be distinguished from Newcastle disease and influenza virus infections by the absence of illness and from infectious bronchitis by the absence of ridges and malformed eggs.
There is however no successful treatment, but the endemic form in breeders can be controlled by strict hygiene, washing and sanitizing incubators and egg trays before reuse. In layers, molting will restore egg production. Prevention is through the control of vertical transmission, by vaccination. Endemic Egg Drop Syndrome is associated with commercial egg-packing stations, as contaminated egg trays can be a major factor in the spread of EDS. The virus is also present in fecal material, hence the importance of strict hygienic procedures.
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