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==Introduction==

==Introduction==

Avian Encephalomyelitis (AE) is commonly known as epidemic tremor in chickens and is caused by a hepatovirus [[avian encephalomyelitis-like virus 1| '''''avian encephalomyelitis-like virus 1''''']] (AEV).  The disease is of economic concern to breeders and layers as it causes a decrease in egg production in laying hens and causes neurological diseases in chicks under three weeks of age.

Avian Encephalomyelitis (AE) is commonly known as epidemic tremor in chickens and is caused by a hepatovirus [[avian encephalomyelitis-like virus 1| '''''avian encephalomyelitis-like virus 1''''']] (AEV).  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'''.

The disease is spread commonly via the '''horizontal''', 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 layer to their chicks.  The virus may be shed for several weeks and cause a decrease in egg hatchability. 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==

==Diagnosis==

==Diagnosis==

The following methods have been used to help diagnose Avian Encephalomyelitis; Virus Neutralization test, Agar Gel test, Embryo Susceptibility test and more recently an '''Elisa test'''.  All of the tests indicate the presense of antibodies but not necessarily the presence of the disease.  Diagnosis can be confirmed by either histopathology or by virus isolation. Classic diagnosis is typically made by the presence of brain lesions shown histologically.

The following methods have been used to help diagnose Avian Encephalomyelitis; Virus Neutralization test, Agar Gel test, Embryo Susceptibility test and more recently an '''Elisa test'''.  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.

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.  

'''Worldwide''', the disease has been documented in Africa, Asia, Australia, Europe, and North and South America.

'''Worldwide''', the disease has been documented in Africa, Asia, Australia, Europe, and North and South America.

==Treatment==

==Treatment==

There is '''no treatment''' for chicks infected with avian encephalomyelitis (AE). Affected chicks that that survive are considered unlikely to be profitable <ref name="Calnek, 2003" />. Surviving chicks will be '''immune to AE for life'''.

There is '''no treatment''' for chicks infected with avian encephalomyelitis (AE). <ref name="Calnek, 2003" />. 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 antibodiesas 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 antibodiesas 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>