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Avian Encephalomyelitis Egg Drop

Extracted From:
A Pocket Guide to
Poultry Health
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By Paul McMullin
© 2004
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Avian encephalomyelitis virus infection in laying bird causes inapparent infection or drops in egg production. See Avian Encephalomyelitis, Epidemic tremors for its effect in young birds. It affects chickens, turkeys, quail, pheasants and occurs in most poultry-producing countries. Morbidity 5-60%, mortality none. The means of transmission is unknown but probably by faecal contamination of environment, feed, water etc. with an oral infection route. Virus in faeces may survive 4 weeks or more. Predisposed by immunosuppression.


  • Drop in egg production, small (5-10%) and lasting no more than 2 weeks.
  • In breeders there may be a drop in hatchability of about 5%, and there is serious disease in the progeny (see next section).

Post-mortem lesions

  • None.


History, rising titre to AE virus, subsequent disease in progeny if breeders. Serology - The embryo protection test has been used in the past, now Elisa is used more commonly. Differentiate from Infectious Bronchitis, lentogenic Newcastle disease, EDS­76.




Vaccination of breeders/layers at 9-15 weeks, attenuated or not. Immunity is usually long lasting.

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