Egg Drop Syndrome (EDS-76)

• EDS-76 is an adenovirus-induced disease of poultry characterized by the production of pale, thin-shelled, soft-shelled, or shell-less eggs.
• It is a disease of laying hens or ducks.
• The full name EDS 76 is used to distinguish it from the flaviviral disease of ducks, which is called ‘egg drop syndrome in ducks’ or ‘duck egg drop syndrome’, creating potential for confusion.

Etiology:

• Duck adenovirus 1, also called Egg Drop Syndrome virus (EDSV)
• ds DNA virus
• virus is resistant to a pH range of 3-10 and to heating for 3 hours at 56°C.
• Infectivity is lost after treatment with 0.5% formaldehyde or 0.5% glutaraldehyde.
• Virus commonly infects both wild and domestic ducks and geese.

Epidemiology:

• This disease was first described in Northern Ireland in 1976
• It is believed to have been introduced in chickens through the use of contaminated vaccine.
• The natural host for this disease is ducks and geese.
• All ages and breeds of chicken are susceptible to infection.
• Disease is most severe in heavy broiler breeders and hens that produce brown eggs.

Transmission:

• Although feces donot contain virus, droppings are contaminated by exudate from oviduct.
• Contaminated needles, biting insects also transmit disease.
• Disease spread in 3 patterns:

i. Classical form:

• Breeders are infected.
• Main method of spread is vertical transmission.
• Infected chicks donot excrete virus until egg production reaches 50%. Virus is reactivated and excreted resulting in lateral spread.

ii. Endemic form:

• Disease spreads laterally between flocks.
• It is due to contaminated egg or trays and usually seen in commercial egg layer.
• Spread is faster in litter system but slow in cage system.

iii. Sporadic form:

• Occurs in occasional isolated cases.
• Occurs through direct contact or indirectly through contaminated water.

Clinical Findings:

• First clinical sign of disease is production of pale-shelled eggs. It is soon followed by thin-shelled, soft-shelled and shell-less egg.
• Eggshell may show mineral deposit.
• Birds are usually healthy; sometimes diarrhea has been described.
• Classical form of disease is characterized by either by drop in egg production by 40-50% around peak or by a failure to achieve or hold expected production.

PM Findings:

• Inactive ovaries and decrease in size of oviduct are only PM findings.
• These findings are not present always.

Diagnosis:

• Sudden fall in egg production, associated with thin-shelled, soft-shelled and shell-less eggs is almost diagnostic.
• Detection of antibodies against egg drop syndrome by HI and SNT
• ELISA
• Isolation of virus in embryonated duck or goose eggs.

Differential Diagnosis:

1. New Castle Disease (ND):

• Absence of illness/severe illness
• Neurological signs are present.

2. Avian influenza (AI):

• Disease spreads rapidly and high mortality
• Respiratory signs; coughing, rales
• Cyanosis of comb, wattle

3. Infectious bronchitis (IB):

• Presence of respiratory signs
• Malformed eggs and thin watery albumen which is absent in EDS 76.

Treatment and Control Measures:

• There is no effective treatment for EDS 76
• Classic form has been eradicated from primary breeders.
• Dedicated equipment should be used for each farm.
• Washing and disinfecting plastic egg trays before use can help to control endemic form.
• Separating chicken from other birds; especially waterfowl to control sporadic form.
• Contaminated water should be chlorinated before use.
• Inactivated vaccines with oil adjuvant are available and if properly administered, prevent the disease successfully. It is administered at age of 14-18 weeks old.