Egg Drop Syndrome (EDS ‘76) is a viral infection that affects chickens, ducks, swans and geese. It can cause a sudden drop in egg production by up to 40%. Egg Drop Syndrome can affect the quality of eggshells (even ones that were laid by healthy birds).
It was first discovered in 1974 in the Netherlands, and was first isolated in Northern Ireland in 1976. Egg Drop Syndrome has caused many issues in European countries including the United Kingdom, Ireland and France, and further outbreaks have been seen across the globe in countries such as India, Japan and Bangladesh.
Egg Drop Syndrome is a double-stranded DNA virus known as Duck Atadenovirus A. The diameter of the Egg Drop Syndrome virus is between 70 and 80mm by negative staining (contrasting thin specimen with an opaque fluid). When chicken flocks are infected with the virus, they fail to reach peak egg production.
The virus can be transmitted vertically from hens to chicks, and remains dormant until chicks reach maturity. Infected chickens can pass the virus through their eggs or droppings.
Egg Drop Syndrome can also be transmitted horizontally between chickens. Generally, this is seen in commercial egg layers when contaminated egg trays are frequently reused. The virus can survive inside the egg itself, and on the outer part of the eggshell. Egg Drop Syndrome can transfer to contaminated egg trays and the other eggs placed on that tray.
When the water supply is contaminated with droppings containing the virus, this can also contribute to the horizontal spread of Egg Drop Syndrome.
The disease has several clinical signs. The first noticeable sign is normal the loss of colour pigmentation in the egg. Afterwards, produced eggs can start appearing soft shelled, thin shelled or shell-less. The thin-shelled and shell-less eggs are very fragile. Often, they can get eaten by chickens. Other signs can include watery egg whites and reduction in egg size and a reduction in egg production.
The virus can cause infected chickens to show signs of loss of appetite, anaemia or temporary diarrhoea.
Egg Drop Syndrome can usually be distinguished from other poultry diseases such as avian influenza (AI) and Newcastle Disease due to its clinical signs. Laboratory testing is needed to eliminate doubts of the diagnosis.
Serological testing can dictate if chickens have antibodies (proteins that protect the body from unwanted substances) against Egg Drop Syndrome. This would suggest that the chicken has been infected with the virus. Serological testing works for non-vaccinated chickens. Vaccinated chickens already cause antibodies to be present.
Treatment and control
To date, there is no treatment for Egg Drop Syndrome. Prevention methods are the best cure to lower the risk of infection. This includes:
- Regularly cleaning all areas including equipment and breeding and laying areas.
- Separate healthy birds from the infected ones.
- Chlorinate contaminated water.
- Vaccinate chickens with an inactivated oil adjuvanted. Examples of vaccines are Nobilis EDS, AVIVAC-EDS-76 and Izovac EDS.
Prevention methods along with putting good biosecurity measures in place can help reduce the risk of your flock being infected with Egg Drop Syndrome.
Advice from biosecurity experts
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