Avian encephalomyelitis (AE) is a viral infection of the central nervous system of poultry, primarily chickens, turkeys, Japanese (coturnix) quail, and pheasants. It is found worldwide and is characterised by ataxia (loss of muscle coordination) and tremors, especially of the head and neck, and a drop in egg production and hatchability in hens. Ducklings, pigeons, and guinea fowl can be infected experimentally. The mortality rate from this disease can be high.
The disease is most common in chickens 1-6 weeks of age. Symptoms usually appear at 7-10 days of age, although they may be present at hatching or delayed for several weeks. Affected chicks may first show a dull expression of the eyes, followed by unsteadiness, sitting on hocks, tremors of the head and neck, paresis (weakness or partial paralysis), and finally total paralysis. Feed and water consumption decreases and birds will lose weight. All stages of the disease can usually be seen in affected flocks. Muscle tremors are best seen after exercising the bird and head tremors are best seen by holding the bird inverted. In adult birds, a slight transient drop in egg production may be the only symptom. The disease in turkeys is often milder than in chickens.
AE is caused by a picornavirus. Vertical transmission is the most common way the disease is spread but it is also spread by direct contact between susceptible hatchlings and infected birds. Most commercial poultry are exposed in the hatchery when 1 day of age, although further spread occurs later within the flock. The virus present in droppings may survive for more than 4 weeks. Recovered birds are immune and do not spread the virus.
There is no treatment for AE. Control of the disease is through prevention. To prevent flocks becoming infected, hatcheries should only accept hatching eggs from immune breeder flocks. Lifetime immunity is acquired through vaccination or recovery from the disease. Breeder pullets should be vaccinated between 9-16 weeks of age. It is also recommended for replacement egg layer pullets to be vaccinated at this age to prevent a temporary drop in egg production.
To minimise the impact of the disease in an infected flock, remove all affected birds and provide good nursing, including fresh food and water, to the remaining birds. Affected birds should be killed and incinerated.