Avian Encephalomyelitis (AE)
or Epedemic Tremor
Cause
Avian encephalomyelitis (AE) is caused by an enterovirus
belonging to the picornavirus group.
Transmission
Egg transmission is the major route of transmission of AE
virus. Infected breeders will transmit the AE virus for several
weeks and cause a decrease in egg hatchability. Infected
chicks that hatch will show clinical signs of the disease and
spread the infection in the incubator to other newly hatched
susceptible chicks. Young chicks can also be infected on the
farm. The incubation period varies from 5 to 14 days depending on the route of infection.
Species affected
Primarily chickens are susceptible to AE, but turkeys and
pheasants have been reported as natural hosts.
Clinical signs
The disease is mainly seen in young chicks, between 1 and 3
weeks of age. Affected chicks sit on their hocks, do not move
well, and many fall on their sides. A fine, rapid trembling of
the head and neck can be seen, but especially felt when affected chicks are held in the hand. In laying and breeding flocks,
AE virus infection causes a marked drop in egg production
which returns to normal in about 2 weeks. Mortality in
naturally infected chicks varies and can be as high as 75%.
45Diagnosis
Clinical tremors in chicks, together with a drop in production
and hatchability in the parent breeders, is indicative of AE
infection. Chicks will not have gross lesions, but histological
examination of brain, proventriculus and pancreas reveals
typical lesions of AE. This will also differentiate the diagnosis
of AE from encephalomalacia (Vitamin A deficiency, crazy
chick disease). Laboratory testing of blood serum from
breeder flocks, or their hatching eggs, can determine if an
infection occurred.
Treatment and control
Preventive vaccination of breeder pullets with live AE vaccine
before egg production is the only effective means of AE
control. If a breeder flock has not been, or has been inadequately, vaccinated against AE and an outbreak occurs, it is
advisable to stop hatching eggs from the flock for several
weeks until the breeders have acquired immunity and no
longer transmit AE virus through their eggs.