Avian encephalomyelitis (AE) Epidemic tremor

Occurrence: Worldwide.
Species affected: All.
Age affected: 1-3 weeks, adults and birds in lay
Causes: Picornavirus.
Effects: Young birds - drowsiness, lack of coordination, unsteady gait, 5-10% mortality. In adults there is a drop in egg production and cataract formation.

Detailed causes:
AE is a peracute disease affecting all poultry species. Young birds from one and three weeks of age and adult birds in lay are affected. The AE virus is a small RNA picornavirus lacking an envelope. It is spread vertically through the egg for 5-12 days after infection and horizontally by contaminated faeces and fomites.

Clinical signs:
Incubation period is 1-7 days. Signs include trembling of the head, lateral recumbency (birds down on their sides), etaxia, and dull eyes. In chicks, drowsiness, lack of coordination, unsteady gait, and mortality of 5-10% is seen in chicks, a drop in egg production and cataracts (opacity of lens) can be seen in adults.

Diagnosis is by virus isolation AE can be confirmed by inoculating susceptible chicks or embryos at 57 days and observing the hatched chicks for clinical signs. Histopathology of the brain (cerebellum), spleen and heart lesions, and virus neutralisation test or ELISA to measure antibodies are helpful. Lateral recumbency in chicks is a presumptive diagnosis for AE. Blindness due to cataracts may develop in chickens that have recovered from an early AE infection during the first three weeks.

Treatment and control:
There is no treatment. Chicks should be purchased only from immune parents. Vaccinate pullets at 10-16 weeks by wingweb or eyedropper. The vaccine spreads rapidly through pullet flocks reared on the floor system (contact with faeces) so all birds do not have to be vaccinated. New recombinant fowl pox vaccine containing part of the AE gene can be given by wing web puncture and will not spread or cause lesions.