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avian encephalomyelitis

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Datasheet

avian encephalomyelitis

Summary

  • Last modified
  • 03 January 2018
  • Datasheet Type(s)
  • Animal Disease
  • Preferred Scientific Name
  • avian encephalomyelitis
  • Overview
  • Avian encephalomyelitis (AE) is most serious in young chicks, pathogenic effects being diminished in birds over two to three weeks of age. Infection of susceptible laying hens can result in temporary decreases in egg...

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Identity

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Preferred Scientific Name

  • avian encephalomyelitis

International Common Names

  • English: avian encephalomyelitis; epidemic tremor in chickens; infectious avian encephalomyelitis

English acronym

  • AE

Overview

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Avian encephalomyelitis (AE) is most serious in young chicks, pathogenic effects being diminished in birds over two to three weeks of age. Infection of susceptible laying hens can result in temporary decreases in egg production; the birds are subsequently protected for life and lay eggs containing maternally derived antibody that provides protection against disease for the chick. Consequently in regions where AE is prevalent it is most appropriate to vaccinate pullets shortly before they come into lay. Vaccination protects them from drops in egg production caused by AE virus (AEV), prevents AEV being transmitted from hen to chick, results in maternal antibody that protects offspring in the vital first three weeks of life and reduces the load of AEV in the environment. There is only one serotype of AEV, vaccines are effective, and immunity is life-long. In addition to chickens, the virus is also known to cause disease in other birds, including turkeys, pheasants and quail, there being serological evidence that other species are susceptible.

The disease was first described as an encephalitis, in the USA during the 1930s. Affected chicks sometimes exhibited ataxia but mainly a rapid tremor of the head and neck. Due to the tremor and the spread of the disease within a flock, the disease acquired the name ‘epidemic tremor’. Subsequently it was observed that tremor was not always evident. So, given the infectious nature of the disease, it was renamed avian encephalomyelitis. The disease has a worldwide distribution.

Hosts/Species Affected

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Neurological avian encephalomyelitis (AE) is manifest in chicks of less than one month of age that do not have maternal immunity. If maternal antibody is present then neurological disease is less likely and less severe. Clinical signs are less in older chicks.

The disease is also known in other galliform birds such as in turkeys (Deshmukh et al., 1971), pheasant (Welchman et al., 2009), guinea fowl (Vivo et al., 1988) and quail (Oladele et al., 2014). Bodin et al. (1981) inoculated three species of game bird, including by the oro-nasal route, with AE virus (AEV). All three species were susceptible, susceptibility being greater in grey partridge (Perdix perdix) than in red-legged partridge (Alectoris rufa) than in pheasant (Phasianus colchicus).

AE has been induced by experimental infection of ducklings, young pigeons and guinea fowl (Calnek, 2003). Steenis (1971) reported naturally occurring antibodies to AEV in sera from turkeys, pheasants, and quail, but not in sera from doves, ducks, finches, jackdaws, pigeons, rooks, sparrows and starlings. Experimental oral exposure of ducks, jackdaws, pigeons and rooks also did not result in AEV antibody production. AE antibodies have been reported in ostrich (Struthio camelus) and rockhopper penguin (Eudyptes chrysocomes) (Karesh et al., 1999).

Distribution

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Avian encephalomyelitis is present in Africa, Asia, Australia, Europe, and North and South America, although there are many countries in these regions for which data is not available.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

AzerbaijanNo information availableOIE Handistatus, 2005
BahrainDisease never reportedOIE Handistatus, 2005
BhutanDisease never reportedOIE Handistatus, 2005
Brunei DarussalamNo information availableOIE Handistatus, 2005
ChinaPresentHao et al., 2014
-Hong KongDisease not reportedOIE Handistatus, 2005
Georgia (Republic of)Disease never reportedOIE Handistatus, 2005
IndiaPresentJana et al., 2005
IndonesiaReported present or known to be presentOIE Handistatus, 2005
IranPresentAsasi et al., 2008
IraqReported present or known to be presentOIE Handistatus, 2005
IsraelNo information availableOIE Handistatus, 2005
JapanNo information availableOIE Handistatus, 2005
JordanDisease not reportedOIE Handistatus, 2005
KazakhstanDisease never reportedOIE Handistatus, 2005
Korea, DPRDisease not reportedOIE Handistatus, 2005
Korea, Republic ofReported present or known to be presentOIE Handistatus, 2005
KuwaitDisease not reportedOIE Handistatus, 2005
LebanonNo information availableOIE Handistatus, 2005
MalaysiaPresentPresent based on regional distribution.
-Peninsular MalaysiaDisease not reportedOIE Handistatus, 2005
-SabahSerological evidence and/or isolation of the agentOIE Handistatus, 2005
-SarawakReported present or known to be presentOIE Handistatus, 2005
MongoliaDisease never reportedOIE Handistatus, 2005
MyanmarLast reported1998OIE Handistatus, 2005
NepalNo information availableOIE Handistatus, 2005
OmanNo information availableOIE Handistatus, 2005
PhilippinesReported present or known to be presentOIE Handistatus, 2005
QatarNo information availableOIE Handistatus, 2005
SingaporeLast reported1987OIE Handistatus, 2005
Sri LankaReported present or known to be presentOIE Handistatus, 2005
SyriaDisease not reportedOIE Handistatus, 2005
TaiwanNo information availableOIE Handistatus, 2005
TajikistanNo information availableOIE Handistatus, 2005
ThailandDisease not reportedOIE Handistatus, 2005
TurkeyNo information availableOIE Handistatus, 2005
TurkmenistanNo information availableOIE Handistatus, 2005
United Arab EmiratesNo information availableOIE Handistatus, 2005
UzbekistanDisease never reportedOIE Handistatus, 2005
VietnamNo information availableOIE Handistatus, 2005
YemenNo information availableOIE Handistatus, 2005

Africa

AlgeriaNo information availableOIE Handistatus, 2005
AngolaNo information availableOIE Handistatus, 2005
BeninNo information availableOIE Handistatus, 2005
BotswanaNo information availableOIE Handistatus, 2005
Burkina FasoNo information availableOIE Handistatus, 2005
BurundiNo information availableOIE Handistatus, 2005
CameroonNo information availableOIE Handistatus, 2005
Cape VerdeDisease not reportedOIE Handistatus, 2005
Central African RepublicDisease not reportedOIE Handistatus, 2005
ChadNo information availableOIE Handistatus, 2005
Congo Democratic RepublicNo information availableOIE Handistatus, 2005
Côte d'IvoireReported present or known to be presentOIE Handistatus, 2005
DjiboutiDisease not reportedOIE Handistatus, 2005
EgyptDisease never reportedOIE Handistatus, 2005
EritreaDisease not reportedOIE Handistatus, 2005
EthiopiaDisease never reportedOIE Handistatus, 2005
GhanaNo information availableOIE Handistatus, 2005
GuineaDisease never reportedOIE Handistatus, 2005
Guinea-BissauNo information availableOIE Handistatus, 2005
KenyaNo information availableOIE Handistatus, 2005
LibyaDisease not reportedOIE Handistatus, 2005
MadagascarDisease never reportedOIE Handistatus, 2005
MalawiNo information availableOIE Handistatus, 2005
MaliNo information availableOIE Handistatus, 2005
MauritiusDisease not reportedOIE Handistatus, 2005
MoroccoNo information availableOIE Handistatus, 2005
MozambiqueNo information availableOIE Handistatus, 2005
NamibiaDisease not reportedOIE Handistatus, 2005
NigeriaPresentOladele and Onwuka, 2013
RéunionNo information availableOIE Handistatus, 2005
RwandaNo information availableOIE Handistatus, 2005
Sao Tome and PrincipeLast reported2000OIE Handistatus, 2005
SenegalNo information availableOIE Handistatus, 2005
SeychellesDisease not reportedOIE Handistatus, 2005
SomaliaNo information availableOIE Handistatus, 2005
South AfricaReported present or known to be presentOIE Handistatus, 2005
SudanPresentJeddah et al., 2007
SwazilandDisease not reportedOIE Handistatus, 2005
TanzaniaNo information availableOIE Handistatus, 2005
TogoDisease never reportedOIE Handistatus, 2005
TunisiaDisease not reportedOIE Handistatus, 2005
UgandaNo information availableOIE Handistatus, 2005
ZambiaNo information availableOIE Handistatus, 2005
ZimbabweDisease not reportedOIE Handistatus, 2005

North America

BermudaDisease not reportedOIE Handistatus, 2005
CanadaReported present or known to be presentOIE Handistatus, 2005
MexicoReported present or known to be presentOIE Handistatus, 2005
USAReported present or known to be presentOIE Handistatus, 2005

Central America and Caribbean

BarbadosReported present or known to be presentOIE Handistatus, 2005
BelizeNo information availableOIE Handistatus, 2005
British Virgin IslandsDisease not reportedOIE Handistatus, 2005
Cayman IslandsDisease not reportedOIE Handistatus, 2005
Costa RicaNo information availableOIE Handistatus, 2005
CubaLast reported1998OIE Handistatus, 2005
CuraçaoDisease not reportedOIE Handistatus, 2005
DominicaDisease not reportedOIE Handistatus, 2005
Dominican RepublicLast reported2003OIE Handistatus, 2005
El SalvadorNo information availableOIE Handistatus, 2005
GuadeloupeNo information availableOIE Handistatus, 2005
GuatemalaNo information availableOIE Handistatus, 2005
HaitiDisease not reportedOIE Handistatus, 2005
HondurasDisease never reportedOIE Handistatus, 2005
JamaicaReported present or known to be presentOIE Handistatus, 2005
MartiniqueNo information availableOIE Handistatus, 2005
NicaraguaNo information availableOIE Handistatus, 2005
PanamaDisease not reportedOIE Handistatus, 2005
Saint Kitts and NevisDisease never reportedOIE Handistatus, 2005
Saint Vincent and the GrenadinesDisease never reportedOIE Handistatus, 2005
Trinidad and TobagoDisease never reportedOIE Handistatus, 2005

South America

ArgentinaReported present or known to be presentOIE Handistatus, 2005
BoliviaNo information availableOIE Handistatus, 2005
BrazilPresentFreitas and Back, 2015
ChileLast reported1988OIE Handistatus, 2005
ColombiaDisease not reportedOIE Handistatus, 2005
EcuadorReported present or known to be presentOIE Handistatus, 2005
Falkland IslandsDisease not reportedOIE Handistatus, 2005
French GuianaDisease not reportedOIE Handistatus, 2005
GuyanaDisease not reportedOIE Handistatus, 2005
ParaguayReported present or known to be presentOIE Handistatus, 2005
PeruNo information availableOIE Handistatus, 2005
UruguayReported present or known to be presentOIE Handistatus, 2005
VenezuelaDisease not reportedOIE Handistatus, 2005

Europe

AndorraNo information availableOIE Handistatus, 2005
AustriaNo information availableOIE Handistatus, 2005
BelarusDisease never reportedOIE Handistatus, 2005
BelgiumNo information availableOIE Handistatus, 2005
Bosnia-HercegovinaNo information availableOIE Handistatus, 2005
BulgariaNo information availableOIE Handistatus, 2005
CroatiaLast reported1996OIE Handistatus, 2005
CyprusDisease not reportedOIE Handistatus, 2005
Czech RepublicDisease not reportedOIE Handistatus, 2005
DenmarkNo information availableOIE Handistatus, 2005
EstoniaDisease never reportedOIE Handistatus, 2005
FinlandReported present or known to be presentOIE Handistatus, 2005
FranceReported present or known to be presentOIE Handistatus, 2005
GermanyOIE Handistatus, 2005
GreecePresentKoutoulis et al., 2015
HungaryPresentMalik, 1969
IcelandDisease never reportedOIE Handistatus, 2005
IrelandReported present or known to be presentOIE Handistatus, 2005
Isle of Man (UK)Disease not reportedOIE Handistatus, 2005
ItalyNo information availableOIE Handistatus, 2005
JerseyDisease never reportedOIE Handistatus, 2005
LatviaDisease never reportedOIE Handistatus, 2005
LiechtensteinDisease not reportedOIE Handistatus, 2005
LithuaniaDisease not reportedOIE Handistatus, 2005
LuxembourgDisease not reportedOIE Handistatus, 2005
MacedoniaDisease not reportedOIE Handistatus, 2005
MaltaDisease not reportedOIE Handistatus, 2005
MoldovaDisease never reportedOIE Handistatus, 2005
NetherlandsReported present or known to be presentOIE Handistatus, 2005
NorwayReported present or known to be presentOIE Handistatus, 2005
PolandNo information availableOIE Handistatus, 2005
PortugalReported present or known to be presentOIE Handistatus, 2005
RomaniaDisease not reportedOIE Handistatus, 2005
Russian FederationDisease not reportedOIE Handistatus, 2005
SlovakiaDisease not reportedOIE Handistatus, 2005
SloveniaDisease not reportedOIE Handistatus, 2005
SpainDisease not reportedOIE Handistatus, 2005
SwedenNo information availableOIE Handistatus, 2005
SwitzerlandNo information availableOIE Handistatus, 2005
UKReported present or known to be presentOIE Handistatus, 2005
-Northern IrelandReported present or known to be presentOIE Handistatus, 2005
UkraineDisease never reportedOIE Handistatus, 2005
Yugoslavia (former)No information availableOIE Handistatus, 2005
Yugoslavia (Serbia and Montenegro)Disease not reportedOIE Handistatus, 2005

Oceania

AustraliaReported present or known to be presentOIE Handistatus, 2005
French PolynesiaReported present or known to be presentOIE Handistatus, 2005
New CaledoniaReported present or known to be presentOIE Handistatus, 2005
New ZealandReported present or known to be presentOIE Handistatus, 2005
SamoaDisease not reportedOIE Handistatus, 2005
VanuatuDisease not reportedOIE Handistatus, 2005
Wallis and Futuna IslandsNo information availableOIE Handistatus, 2005

Pathology

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The gross lesion associated with avian encephalomyelitis virus (AEV) infection is whitish areas in the muscularis of the ventriculus, due to infiltrating lymphocytes (Calnek, 2003). Microscopic lesions have been observed in the central nervous system (CNS) and in some visceral tissues such as the proventriculus and pancreas. Calnek (2003) has summarized microscopic findings. In the CNS there is a disseminated, non-purulent encephalomyelitis and a ganglionitis of the dorsal root ganglia. There is a perivascular infiltrate in all portions of the brain and spinal chord, except in the cerebellum, where it is confined to the nucleus (n) cerebellaris.

Calnek (2003) has described a number of lesions that can be considered to be pathognomonic; in the midbrain, two nuclei, rotundus and ovoidalis are, invariably affected with a loose microgliosis; and central chromatolysis (axonal reaction) of the neurons in the nuclei of the brain stem, especially those of the oblongata. The proventriculus exhibits another pathognomonic change, obvious dense nodules in the muscular wall. AE causes the number of lymphocyte follicles in the pancreas to increase several-fold.

Diagnosis

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Clinical diagnosis

Avian encephalomyelitis (AE) is largely a disease of chicks of up to two to three weeks of age. A dullness of the eyes is seen, which becomes more pronounced. There is progressive ataxia, although this is not always observed. The chicks in later stages sit on their hocks and some move whilst still on their hocks or shanks. When they move they have poor coordination and may fall on their sides. There may be fine tremors of the head and neck, though these may not be apparent in all birds, and severity is variable. Ataxic signs usually, but not always, appear before tremor. Chicks older than two to three weeks of age are less unlikely to demonstrate the above clinical signs. Birds in lay do not exhibit neurological signs, though may have a temporary drop in egg production.

Lesions

The gross lesion associated with AE virus (AEV) infection is whitish areas in the muscularis of the ventriculus, due to infiltrating lymphocytes (Calnek, 2003). Microscopic lesions have been observed in the central nervous system (CNS) and in some visceral tissues such as the proventriculus and pancreas. Calnek (2003) has recently summarized microscopic findings. In the CNS there is a disseminated, non-purulent encephalomyelitis and a ganglionitis of the dorsal root ganglia. There is a perivascular infiltrate in all portions of the brain and spinal chord, except in the cerebellum, where it is confined to the nucleus (n) cerebellaris.

Calnek (2003) has described a number of lesions that can be considered to be pathognomonic; in the midbrain, two nuclei, rotundus and ovoidalis are, invariably affected with a loose microgliosis; and central chromatolysis (axonal reaction) of the neurons in the nuclei of the brain stem, especially those of the oblongata. The proventriculus exhibits another pathognomonic change, obvious dense nodules in the muscular wall. AE causes the number of lymphocyte follicles in the pancreas to increase several-fold.


Differential diagnosis


The clinical signs of AE are similar to those of some other diseases: Newcastle disease (ND), equine encephalomyelitis infection, nutritional disturbances (rickets, encephalomalacia, riboflavin deficiency), and Marek’s disease (Calnek, 2003). Consequently various factors should be taken into account before reaching a diagnosis, including the age of the chicks (typical signs of AE are usually only seen in chicks of up to two to three weeks of age), the AEV immunity status of the parent flocks and histopathological analysis. Although typical AE is associated with very young chicks, ND can affect birds of the same age. The pathognomic lesions described above differentiate AE from ND. Encephalomalacia generally occurs two to three weeks later than AE and the lesions revealed by histopathological analysis are very different from those of AE. Marek’s disease occurs in older chicks and exhibits changes not seen in AE; peripheral nerve involvement and the nature of lymphomatosis of visceral organs is different.


Laboratory diagnosis

Tannock and Shafren (1994) have reviewed the use of chicks, embryos and various cell cultures for the isolation and propagation of AEV. Chicks and embryos must be from AEV-susceptible flocks. Day-old chicks are inoculated intracerebrally, whilst embryos are inoculated via the yolk-sac at 6 to 7 days of age. Some strains have been adapted to grow in embryos, the most widely used adapted strain being that of Van Roekel. Growth of field strains in various cell cultures usually results in low titres. Chicken embryo brain cells have been used, although these tend to be overgrown by fibroblasts. Chick embryo fibroblasts, chicken embryo kidney cells and chicken pancreatic cells have been used, but with very low yields of AEV. Liu et al. (1999) described the use of the mammalian continuous cell line BGM-70 for the isolation of AEV from the brain of diseased broilers. The authors observed cytopathic effect by the third passage.

Various agar gel precipitin (AGP) tests have been devised to detect antibody to AEV, summarized by Tannock and Shafren (1994). Extracts of the brain or gastrointestinal tract of experimentally inoculated susceptible embryos have been used as the source of antigen for the AGP test, with conflicting results as to which source is best. Although an inexpensive test, the AGP test has largely been replaced by ELISAs, the results from which have been shown to correlate well with the results of virus neutralization tests. Tannock and Shafren have described the AEV ELISAs as being ‘sensitive, specific, rapid, relatively cheap and amenable to large scale screening.’ Procedures for ELISAs include those of Smart and Grix (1985), Smart et al. (1986), Garrett et al. (1984) and an improved procedure of Shafren et al. (1989). An antigen-capture ELISA, to detect AEV in embryo and chicken tissues, has also been described (Shafren and Tannock, 1988).

Real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assays for rapid detection of AEV have been described (Liu et al., 2014; Xue et al., 2016).

List of Symptoms/Signs

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SignLife StagesType
General Signs / Ataxia, incoordination, staggering, falling Sign
General Signs / Dysmetria, hypermetria, hypometria Sign
General Signs / Exercise intolerance, tires easily Poultry:Day-old chick Sign
General Signs / Inability to stand, downer, prostration Sign
General Signs / Increased mortality in flocks of birds Sign
General Signs / Lameness, stiffness, stilted gait in birds Poultry:Day-old chick Diagnosis
General Signs / Reluctant to move, refusal to move Poultry:Day-old chick Sign
General Signs / Trembling, shivering, fasciculations, chilling Sign
General Signs / Underweight, poor condition, thin, emaciated, unthriftiness, ill thrift Sign
General Signs / Weakness, paresis, paralysis of the legs, limbs in birds Sign
General Signs / Weakness, paresis, paralysis, drooping, of the wings Sign
General Signs / Weight loss Sign
Nervous Signs / Dullness, depression, lethargy, depressed, lethargic, listless Sign
Nervous Signs / Tremor Sign
Ophthalmology Signs / Blindness Poultry:Day-old chick,Poultry:Young poultry Sign
Ophthalmology Signs / Cataract, lens opacity Sign
Reproductive Signs / Decreased hatchability of eggs Sign
Reproductive Signs / Decreased, dropping, egg production Sign
Respiratory Signs / Change in voice, vocal strength Poultry:Young poultry Sign
Respiratory Signs / Hoarse chirp in birds Poultry:Day-old chick Sign

Disease Course

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The manifestation of avian encephalomyelitis (AE) depends on age and immune status. Chicks of less than one month of age from non-immune hens develop neurological disease, which can be fatal. Chicks hatched from eggs laid during an outbreak of AE develop neurological disease. In these circumstances the virus induces paralysis, ataxia and muscular dystrophy (Tannock and Shafren, 1994; Calnek, 2003). Older chicks exhibit fewer neurological signs and in more mature birds the infection can be unapparent, though there can be a temporary drop in egg production and hatchability. Chicks and older birds are protected from neurological signs by maternal antibody. The course of the disease in turkeys is similar to that in chickens (Holstein et al., 1970).

The virus is presumed to replicate first in epithelial cells of the alimentary tract; immunofluorescence revealed infected cells in the epithelium of the tunica mucosa of the duodenum, and in the proventriculus, jejunum and caecum (Miyamae, 1983). Afterwards the virus is believed to enter the bloodstream and spread to other organs and the central nervous system. The oral-faecal is thought to be the main route of infection, virus being detected in faeces within three days of oral administration (Calnek, 1998) Shedding may continue for more than two weeks in very young chicks but those over three weeks of age may shed virus for only about five days (Calnek, 2003). Although this is a major route of spread, the virus also spreads vertically. Following experimental infection of laying hens, infected embryos were laid in the following 5- to 13-day period. Infected eggs may exhibit reduced hatchability. Contact transmission can occur in the incubator as well as in the brooder.

Morbidity and mortality within a very young flock will vary depending on the AE history of the laying flocks from which the chicks collectively were derived; if the laying birds were immune to AE virus, their chicks will not develop the typical clinical signs of AE, in contrast to chicks originating from non-immune flocks. Chicks from an infected laying flock may exhibit morbidity of 40 to 60%, with mortality averaging 25%.

Surviving birds develop lifelong immunity, attributed to circulating antibody, though some become blind.

Epidemiology

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Avian encephalomyelitis (AE) has been most thoroughly studied in the domestic fowl, though the course of the disease in turkeys is similar. In regions where AE virus (AEV) is present, nearly all laying flocks will become infected. If they have been vaccinated, then clinical signs are unlikely to be apparent. Natural field strains are enterotropic. The virus replicates in the alimentary tract and is shed in faeces during the second week after infection. Shedding ceases as specific antibody is produced. It spreads horizontally, by the faecal-oral route, and also vertically. Birds can also become infected by the oral route, (a route by which live AE vaccines can be applied), though the faecal-oral route is considered to be the main route of natural infection. The nature of the disease depends on age and immune status. Chicks of less than one month of age from non-immune hens develop neurological disease, which can be fatal. Chicks hatched from eggs laid during an outbreak of AEV develop neurological disease.

Older chicks exhibit fewer neurological signs and in more mature birds the infection can be unapparent. Chicks are protected from neurological signs by maternal antibody. Vectors are not known to be involved; presence of virus in faeces is sufficient for transmission. AEV is quite stable, remaining in a contaminated area for long periods. There is only one serotype and immunity is life-long.

The disease is also known in other galliform birds: turkeys, pheasant and quail. AE has been induced by experimental infection of ducklings, young pigeons and guineafowl (Calnek 2003). Steenis (1971) reported naturally occurring antibodies to AEV in sera from turkeys, pheasants and quail, but not in sera from doves, ducks, finches, jackdaws, pigeons, rooks, sparrows and starlings. Experimental oral exposure of ducks, jackdaws, pigeons and rooks also did not result in AEV antibody production. AE antibodies have been reported in ostrich and penguin.

Impact: Economic

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Susceptible layers have a temporary drop in egg production, which can be substantial. Young chicks can be killed. The economic importance of avian encephalomyelitis (AE) was greatly reduced when AE vaccines became available commercially.

Zoonoses and Food Safety

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Avian encephalomyelitis has no public health significance.

Disease Treatment

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There is no treatment for affected chicks with avian encephalomyelitis (AE). Affected chicks that do not die are considered unlikely to be profitable (Calnek, 2003). Surviving chicks will be immune to AE for life.

Prevention and Control

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Control of avian encephalomyelitis (AE) is best achieved by vaccination of breeders or commercial layers with live embryo-attenuated virus several weeks before they come into lay. Calnek (1998) suggests that vaccination should be after eight weeks of age and at least four weeks before egg production. One objective of vaccination is to prevent replication of field virus so that there will be no vertical transmission of the virus to progeny. A second objective is to ensure that there are maternally derived antibodies to protect the chicks; AE virus (AEV) has its greatest effect in chicks of up to three weeks of age. Lastly, vaccination protects against drops in egg production caused by infection of mature layers. Inactivated AE vaccines may be given if previously non-vaccinated flocks that are in lay are believed to be at risk, or if application of live AE vaccine is contraindicated. Vaccination gives life-long immunity. Protection of progeny to infection correlates with the titre of antibody in the layers (Garrett et al., 1985). Anti-AE maternal antibody can be detected in chicks for up to 21 days after hatch (Shafren et al., 1992).

AE vaccines are produced using embryo-propagated AEV virus. Shafren and Tannock (1990) have described an ELISA-based method, involving embryos, for assessing the infectivity of AE vaccines that is much faster than the conventional method that involves chicks. Care must be taken not to adapt the virus to embryos, as one consequence of adaptation is selection of virus that no longer replicates well in the gut when applied by eye-drop or in drinking water, thus resulting in poor stimulation of immunity. Embryo-adapted virus given by wing-web application can result in clinical disease (Glisson and Fletcher, 1987). Calnek (1998) has reviewed the development of AE vaccines.

Live AE vaccine can be administered in drinking water. Shafren et al. (1992) compared the efficacy of antibody production, measured by ELISA, after vaccination by eye-drop with that achieved by drinking water application. They found that vaccination by eye-drop of only 10% of a flock gave the same results as drinking water application; the vaccinal virus spread to the littermates. However, when only 5% of the birds received the vaccine by eye-drop, the spread of the virus within the flock was not good enough for vaccination purposes.

Smyth et al. (1994) reported instances of clinical AE following live AE vaccination of 14-week-old chickens. Two to five weeks after vaccination, mortality reached 2%. The authors postulated that the birds had earlier been immunosuppressed, in one case probably by Marek’s disease virus, resulting in the vaccinal AE being able to produce severe lesions and mortality. The authors demonstrated by experiment that, contrary to popular opinion, AE vaccine given orally can spread to the central nervous system and produce mild encephalitis. Not withstanding, under good conditions and with proper application live attenuated AE vaccines are very good at controlling AE. AE vaccines can also be used in turkeys (Deshmukh et al., 1974).

References

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Asasi K; Farzinpour A; Tafti AK, 2008. Clinico-pathological studies on avian encephalomyelitis in Shiraz, Iran. Turkish Journal of Veterinary & Animal Sciences, 32(3):229-231. http://journals.tubitak.gov.tr/veterinary/

Bodin G; Pellerin JL; Milon A; Geral MF; Berthelot X; Lautie R, 1981. Experimental infection of game birds (pheasants, red-legged partridges, grey partridges) with avian encephalomyelitis virus. Revue de Medecine Veterinaire, 132(12):805-816.

Calnek BW, 1998. Control of avian encephalomyelitis: a historical account. Avian Diseases, 42(4):632-647; 59 ref.

Calnek BW, 2003. Avian Encephalomyelitis. In: Saif YM, Barnes HJ, Glisson JR, Fadly AM, McDougald, LR, Swayne DE, eds. Diseases of Poultry. Ames, Iowa, USA: Iowa State Press, 271-282.

Decaesstecker M; Meulemans G, 1989. Antigenic relationships between fowl enteroviruses. Avian Pathology, 18(4):715-723; 16 ref.

Deshmukh DR; Hohlstein WM; McDowell JR; Pomeroy BS, 1971. Prevalence of avian encephalomyelitis in turkey breeder flocks. American Journal of Veterinary Research, 32(8):1263-1267.

Deshmukh-DR; Patel-BL; Pomeroy-BS, 1974. Duration of immunity in recycled turkey breeder hens vaccinated with a single dose of live avian encephalomyelitis virus vaccine. American Journal of Veterinary Research, 35(11):1463-1464.

Freitas ESde; Back A, 2015. New occurance of avian encephalomyelitis in broiler - is this an emerging disease? Brazilian Journal of Poultry Science, 17(3):399-404. http://www.scielo.br/pdf/rbca/v17n3/1516-635X-rbca-17-03-00399.pdf

Garrett JK; Davis RB; Ragland WL, 1984. Enzyme-linked immunosorbent assay for detection of antibody to avian encephalomyelitis virus in chickens. Avian Diseases, 28(1):117-130; 27 ref.

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