Avian Encephalomyelitis (AE)
Avian encephalomyelitis (AE) is a viral disease of young chickens caused by a virus from the Hepatovirus family and characterised by central nervous system signs (Epidemic Tremors). Primarily a viral infection of poultry, chickens, turkey and pheasants. First reported in 1932, the virus grows in the yolk sac and brain of the chicken embryo in eggs from nonimmune hens. Most prevalent in chickens 1 to 6 weeks of age. Susceptible chickens more than 5 weeks old will develop antibodies to AE, but do not show clinical signs at the time of infection.
AE occurs world wide and occurs in all seasons of the year, but most cases are reported from January to June. Egg-passage transmission from infected hen to chick is the most common mode of spread, but direct contact of susceptible hatchlings with infected birds accounts for spread within the flock. Indirect spread via fecal contamination of feed and water also occurs. The virus can survive at least 4 weeks in droppings.
Clinical signs appear at 7 to 10 days of age. Tremors of the head and neck are presumptive of the disease in the flock hence the name "Epidemic tremor". Affected chicks first may show a dull expression of the eyes, followed by progressive in coordination, sitting on hocks, tremors of the head and neck, and finally paralysis or prostration.
Muscular tremors are best seen by exercising the bird. Affected birds are inactive; some may refuse to walk or walk on their hocks. Diagnosis is confirmed by fluorescent antibody test, virus isolation and agar gel precipitin test. AE must be differentiated from other encephalitic diseases such as ND, EEE, MD etc.