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==Introduction==

==Introduction==

Avian Encephalomyelitis (AE) is commonly known as epidemic tremor in chickens.  It is caused by the hepatovirus ''Avian encephalomyelitis-like virus 1''(AEV)'''single-stranded RNA''' (ssRNA) viruses.  It was formerly classified as an ''enterovirus'' but is now considered a '''''Hepatovirus''''' as its genome ecodes for a single polyprotein (2134 amino acids), which shares greater resemblance to that of the hepatitis A viruses than the other picornavirus genera.

Avian Encephalomyelitis (AE) is commonly known as epidemic tremor in chickens.  It is caused by ''Avian encephalomyelitis-like virus 1''(AEV)''' which is a single-stranded RNA''' (ssRNA) virus belonging to the [[Picornaviridae| '''''Picornaviridae''''']] family.  It was formerly classified as an ''enterovirus'' but is now considered a '''''Hepatovirus''''' as its genome ecodes for a single polyprotein (2134 amino acids), which shares greater resemblance to that of the hepatitis A viruses than the other picornavirus genera. The virus has a non-enveloped capsid with icosahedral symmetry and approximately 26 nm in diameter and a buoyant density of 1.31 g/ml in caesium chloride <ref>Tannock, G.A., Shafren, D.R., (1994) '''''Avian encephalomyelitis: a review'''''. ''Avian Pathology'', 23(4):603-620; 85 ref.</ref>.  There is only one serotype of AEV, which is not related antigenically to other avian picoronaviruses, which is why it has been referred to in the past as an enteroviruses or enterovirus-like viruses.  

It belongs to the familiy [[Picornaviridae| '''''Picornaviridae''''']]. AEV causes the disease known as [[Avian Encephalomyelitis| '''''avian encephalomyelitis''''']].

 

.  The disease is of economic concern to breeders and layers as it causes a '''decrease in egg production''' in laying hens, a '''decrease in egg hatchability''', '''neurological diseases in chicks under three weeks of age''' and '''affected chicks that that survive are considered unlikely to be profitable'''.

Avian Encephalomyelitis (AE)is of economic concern to breeders and layers as it causes a '''decrease in egg production''' in laying hens, a '''decrease in egg hatchability''', '''neurological diseases in chicks under three weeks of age''' and '''affected chicks that that survive are considered unlikely to be profitable'''.

The disease is spread '''horizontally''', via the faecal-oral route and chicks from non-immune layers under the age of three weeks are neurologically affected.  '''Vertical transmission''' can also occur from infected layers to their chicks.  The virus may be shed for several weeks. Once a bird becomes infected with the disease or is vaccinated it is immune to AE for life, some birds are left blind.  AE is not considered a zoonosis.

The disease is spread '''horizontally''', via the faecal-oral route and chicks from non-immune layers under the age of three weeks are neurologically affected.  '''Vertical transmission''' can also occur from infected layers to their chicks.  The virus may be shed for several weeks. Once a bird becomes infected with the disease or is vaccinated it is immune to AE for life, some birds are left blind.  AE is not considered a zoonosis.

==Signalment==

==Signalment==

The domestic host for AEV is the '''chicken''' but it can also infect species of '''partridge, turkey, quail, guineafowl and pheasants'''. The infection causes the most serious disease in chicks under 3 weeks of age and older chicks show fewer clinical signs.  Laying hens show a temporary reduction in their  productivity . The incubation period varies from 5 to 14 days depending

The domestic host for AEV is the '''chicken''' but it can also infect species of '''partridge, turkey, quail, guineafowl and pheasants'''. The infection causes the most serious disease in chicks under 3 weeks of age and older chicks show fewer clinical signs.  Laying hens show a temporary reduction in their  productivity . The incubation period varies from 5 to 14 days depending on the route of infection.

on the route of infection.

==Clinical Signs==

==Clinical Signs==

The disease causes a range of '''neurological signs''' in '''chicks under 3 weeks''', ranging from ataxia, '''rapid tremor of the head and neck''', drooping of the wings, weakness, paralysis, exercise intolerance to '''blindness''' and changes in vocalisation.  It also causes weight loss, lameness, and unthriftiness.  Affected chicks '''sit on their hocks''', and cannot move well and many '''fall over onto their sides'''. Mortality can be as high as 25% with higher morbity rates of up to 60%. Older chicks show fewer neurological signs and in laying hens the disease causes a '''temporary reduction (2 weeks) in egg production''' and a '''decrease in droppings'''.

The disease causes a range of '''neurological signs''' in '''chicks under 3 weeks''', ranging from ataxia, '''rapid tremor of the head and neck''', drooping of the wings, weakness, paralysis, exercise intolerance to '''blindness''' and changes in vocalisation.  It also causes weight loss, lameness, and unthriftiness.  Affected chicks '''sit on their hocks''', and cannot move well and many '''fall over onto their sides'''. Mortality can be as high as 25% with higher morbity rates of up to 60%. Older chicks show fewer neurological signs and in laying hens the disease causes a '''temporary reduction (2 weeks) in egg production''' and a '''decrease in droppings'''.

==Diagnosis==

==Diagnosis==