Egg drop syndrome

Overview

Egg drop syndrome (EDS), also known as egg drop syndrome-1976 (EDS-76), is a viral disease that affects egg-laying birds, primarily chickens and ducks. It is characterized by a sudden drop in egg production, poor shell quality, and the laying of shell-less or soft-shelled eggs. The disease is economically significant in the poultry industry due to its impact on productivity and egg quality. EDS is caused by a duck adenovirus and can spread rapidly within a flock if not properly managed.

Causes

Egg drop syndrome is caused by the duck adenovirus 1 (a member of the genus Atadenovirus). The virus originally infected ducks but has since adapted to infect chickens. Transmission can occur in several ways:

• Vertical transmission: Infected breeders can pass the virus to offspring through the egg.

• Horizontal transmission: Via contaminated water, equipment, or direct contact between birds.

• Contaminated vaccines: In rare cases, live vaccines derived from duck embryos may carry the virus.

Birds may remain asymptomatic carriers of the virus and shed it intermittently, contributing to ongoing spread within a flock.

Symptoms

Clinical signs of EDS usually appear in apparently healthy laying birds. The most prominent symptoms include:

• Sudden drop in egg production (up to 40–50%)

• Poor shell quality: thin, soft, or shell-less eggs

• Discoloration or rough-shelled eggs

• Watery albumen (egg white)

• Eggs laid outside of nesting boxes

• Little to no signs of illness in the birds themselves

Unlike many poultry diseases, EDS does not typically cause significant mortality or systemic illness, which can delay recognition.

Diagnosis

Diagnosis of EDS is based on clinical signs, laboratory tests, and exclusion of other causes of decreased egg production. Diagnostic procedures may include:

• Serological tests: ELISA or hemagglutination inhibition (HI) tests to detect antibodies against the virus

• Virus isolation: From cloacal swabs, oviducts, or albumen in embryonated duck or chicken eggs

• Polymerase chain reaction (PCR): To identify viral DNA

• Histopathology: Examination of reproductive tract tissues may reveal inflammation or damage

• Exclusion of other diseases: Such as Newcastle disease or infectious bronchitis

Treatment

There is no specific antiviral treatment for egg drop syndrome. Management focuses on prevention and controlling the spread of the virus:

• Vaccination: Inactivated EDS vaccines are available and effective when administered before the onset of laying (usually at 14–18 weeks of age)

• Biosecurity: Strict hygiene, equipment disinfection, and limiting outside bird contact help prevent introduction of the virus

• Avoid contaminated vaccines: Only use certified virus-free vaccines and vaccine production methods

• Supportive care: Maintaining optimal nutrition, lighting, and housing conditions to minimize stress and support recovery

Prognosis

With proper vaccination and biosecurity, egg drop syndrome can be effectively controlled and prevented. In flocks where EDS occurs, egg production and quality typically recover over several weeks, although some economic loss is inevitable. Recovered birds usually return to normal laying patterns, but may continue to carry the virus. The prognosis for individual birds is good, as the disease rarely causes serious illness or death.