Occurrence: Worldwide.
Species affected: All.
Age affected: 1-3 weeks and adults.
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.
Avian encephalomyelitis (AE)
AE is a peracute disease affecting all poultry species. Young birds between one and three weeks of age and adult birds are affected. The AE virus is a small RNA picornavirus lacking an envelope. It is spread vertically through the egg for 42 days after infection and by contaminated faeces and fomites.
Incubation period is 1-7 days. Signs include trembling of the head, lateral recumbency (birds down on their sides), ataxia, 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 by inoculating embryos at 5-7 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 or cataracts in adults are a presumptive diagnosis for AE.
There is no treatment. Chicks should be purchased only from clean or immune parents. Vaccinate pullets (1-20%) at 10-16 weeks by wing-web or eyedropper. The vaccine spreads rapidly through pullet flocks 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.