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Also known as: '''''AE''''' — '''''Epidemic Tremor in Chickens''''' — '''''Avian Encephalomyelitis Virus — AEV'''''

Also known as: '''''AE''''' — '''''Epidemic Tremor in Chickens''''' — '''''Avian Encephalomyelitis Virus — AEV'''''

{{Taxobox

{{Taxobox

==Introduction==

==Introduction==

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 encodes 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 is approximately 26 nm in diameter and has 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>.  ''Avian encephalomyelitis-like virus 1'' 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.  

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 shares greater resemblance with that of the ''hepatitis A viruses'' than the other picornavirus genera.  The virus has a non-enveloped capsid with icosahedral symmetry and is approximately 26 nm in diameter and has buoyant density of 1.31 g/ml in caesium chloride.  ''Avian encephalomyelitis-like virus 1'' 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.  

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 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 survive are considered unlikely to be profitable'''.

==Epidemiology==

==Epidemiology==

The virus replicates in the epithelial cells of the alimentary tract and is circulated in the bloodstream to other organs and the central nervous system (CNS). The virus is shed within 3 days of oral ingestion and in young chicks can continue to be shed for over two weeks. Shedding ceases once specific antibody's are produced. 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.   

The virus replicates in the epithelial cells of the alimentary tract and is circulated in the bloodstream to other organs and the central nervous system (CNS). The virus is shed within 3 days of oral ingestion and in young chicks can continue to be shed for over two weeks. Shedding ceases once specific antibodies are produced. 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.  

'''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.  

:Agar gel test

:Agar gel test

:Embryo susceptibility test  

:Embryo susceptibility test  

:and more recently an [[ELISA testing|'''Elisa test''']]<br>

:and more recently an [[ELISA testing|'''ELISA''']]<br>

All of the tests show the presence of antibodies and indicate exposure to the disease and not necessarily a current infection. Diagnosis can be confirmed by either histopathology or by virus isolation. Classic diagnosis is typically made by the presence of brain lesions shown histologically.

All of the tests show the presence of antibodies and indicate exposure to the disease and not necessarily a current infection. Diagnosis can be confirmed by either histopathology or by virus isolation. Classic diagnosis is typically made by the presence of brain lesions showing histologically.

'''Pathology'''<br>

'''Pathology'''<br>

Grossly, lymphocytic infiltration of the muscular region of the ventriculus has also been noted as well as perivascular infiltration within the brain and chord, with the exception of the cerebellum, where lesions can be found only in the nucleus cerebellaris.  '''Pathognomonic lesions can be found within the midbrain and rotundua and ovidalis nucleus  (microglisosis)''' and '''proventriculus (dense nodules within the muscular wall)'''.  Lesions can also be present in the pancreas.  

Grossly, lymphocytic infiltration of the muscular region of the ventriculus has also been noted as well as perivascular infiltration within the brain and chord, with the exception of the cerebellum, where lesions can be found only in the nucleus cerebellaris.  '''Pathognomonic lesions can be found within the midbrain and rotundua and ovidalis nucleus  (microglisosis)''' and '''proventriculus (dense nodules within the muscular wall)'''.  Lesions can also be present in the pancreas.  

'''Differential diagnoses''' include [[Newcastle Disease Virus|Newcastle disease (ND)]], [[Equine Viral Encephalitis|Equine encephalomyelitis infection]], nutritional disturbances ([[Rickets|rickets]], encephalomalacia, riboflavin deficiency), and [[Mareks Disease|Marek’s disease]] <ref name="Calnek, 2003">Calnek, B.W.(2003) '''Avian Encephalomyelitis'''. In: Saif, Y.M., Barnes, H.J., Glisson, J.R., Fadly, A.M., McDougald, L.R., Swayne, D.E., eds. Diseases of Poultry. Ames, Iowa, USA: ''Iowa State Press'', 271-282.</ref>

'''Differential diagnoses''' include [[Newcastle Disease Virus|Newcastle disease (ND)]], nutritional disturbances ([[Rickets|rickets]], encephalomalacia, riboflavin deficiency), and [[Mareks Disease|Marek’s disease]].

==Distribution==

==Distribution==

==Treatment==

==Treatment==

There is '''no treatment''' for chicks infected with avian encephalomyelitis.  <ref name="Calnek, 2003" />. Surviving chicks will be '''immune to AE for life'''.

There is '''no treatment''' for chicks infected with avian encephalomyelitis. Surviving chicks will be '''immune to AE for life'''.

==Control==

==Control==

In regions where AE is prevalent, an effective way of preventing AE is to '''vaccinate pullets''' several weeks before they come into lay. Vaccination protects the flock from a reduction in egg production and prevents vertical transmission of the virus to chicks by providing the chicks with a sufficient level of maternal derived antibodies because there is only one serotype for the AEV.  There are live and attenuated vaccinations available which can be administered in '''drinking water''' or as an '''eye drop''', the latter being more effective. Vaccination by eye-drop of only 10% of a flock gave the same results as drinking water application <ref name="Shafren, 1992">Shafren, D.R., Tannock, G.A., Groves, P.J. (1992) '''Antibody responses to avian encephalomyelitis virus vaccines when administered by different routes'''. ''Australian Veterinary Journal'', 69(11):272-275; 10 ref.</ref>

In regions where AE is prevalent, an effective way of preventing AE is to '''vaccinate pullets''' several weeks before they come into lay. Vaccination protects the flock from a reduction in egg production and prevents vertical transmission of the virus to chicks by providing the chicks with a sufficient level of maternal derived antibodies because there is only one serotype for the AEV.  There are live and attenuated vaccinations available which can be administered in '''drinking water''' or as an '''eye drop''', the latter being more effective. Vaccination by eye-drop of only 10% of a flock gave the same results as drinking water application.

==References==

==References==

{{CABI source

{{CABI source

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|date = 25/06/2011

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[[Category:Hepatoviruses]]

[[Category:Hepatoviruses]]

[[Category:Avian Viruses]]

[[Category:Avian Viruses]]

[[Category:Reproductive Diseases - Birds]]

[[Category:Reproductive Diseases - Birds]]

[[Category:Neurological Diseases - Birds]]

[[Category:Neurological Diseases - Birds]]

[[Category:CABI Expert Review]]

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