Avian encephalomyelitis is a viral disease that affects young chickens between 1-2 weeks of age. It is caused by an enterovirus from the picornaviridae family. The virus is resistant to many physical and chemical agents but can be killed by formaldehyde. Infected chickens may show depression, muscular incoordination, tremors and reduced egg production. Upon examination, white areas can be seen in the gastrointestinal tract and histopathological examination reveals changes in the central nervous system. There is no effective treatment for infected birds so control relies on vaccination, sanitation and destroying affected flocks.

1. Prepared By
Dr. Sushil Neupane
Institute of Agriculture and Animal Science(IAAS)
Paklihawa Campus, Rupandehi, Nepal
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AVIAN ENCEPHALOMYELITIS

2. INTRODUCTION
 Viral disease of young chicken
 Characterized by muscular incoordination and rapid tremors,
esp. of head and neck so often known as ‘epidemic tremor’
 Affects adults, but most flocks show no clinical signs of the disease
other than drop in egg production

3. ETIOLOGY
 Enterovirus, non-enveloped single-stranded RNA virus of
picorna viridae family
 Relatively resistant to physical and chemical agents as well
heat and cold
 Resistant to: chloroform, trypsin, pepsin
 Susceptible to: formaldehyde fumigation
 Affinity for enteric and nervous tissues

4. EPIDEMIOLOGY
 It is a disease of young chickens (1 to 2 weeks)
 First reported in 2 week-old Rhode island chicks from a
commercial flock(jones, 1932)
 Emerging disease in all the corners of the world
 Morbidity rate is 40 to 60%; Mortality is 25% and may exceed
50%

5. SUSCEPTIBLE HOST
 Disease occurs in poultry, turkeys, Japanese quail and
pheasants
 Baby chicks of 1-2 weeks of age are mostly susceptible
 Human beings aren't affected

6. TRANSMISSION
 Vertical transmission (through egg)
 Contaminated water and feed
 Fomites
 Infected chicks (horizontal)

7. PATHOGENESIS
Young chicks are infected orally
Primary infection of the alimentary tract especially in the duodenum.
Viremia
Subsequent infection of the pancreas and other visceral organs (liver, heart, kidney
and spleen) and skeletal muscle and finally the CNS

8. .
 Mortality is due to inability of the chicks to reach to food and
water.
Purkinje cells and the molecular layer of the cerebellum are apparently favored sites of
virus replication.
Persistence of virus infection is common in the CNS, alimentary tract and pancreas.

9. SYMPTOMS
 Incubation period(chicks which hatch) : 1-7 days
 Incubation period(chicks which are infected after hatching) : 11
days
 Young chicks are primarily affected with high morbidity and
mortality.
 Depression, muscular incoordination(ataxia), tremors
 In layers, there is drop of egg production with reduced
hatchability (5-10%)
 Nervous symptom at 1 week of age

10. SYMPTOMS

11. POSTMORTEM FINDINGS
 Whitish areas in gizzard and proventriculus caused by masses of
lymphocytes.
 Histopathological examination of pons, medulla and spinal cord
show eccentricity and chromatolysis of nucleus.
 Non- purulent encephalomyelitis is observed.
 Gliosis occurs in molecular layer of cerebellum.
 Central chromatolysis of neurons of brain stem .
 Huge lymphocytic proliferation in proventriculus, pancreas,
gizzard and heart muscles.

12. Fig: Central Chromatolysis of Neuron

13. Whitish areas in muscle of the gizzard and proventriculus

14. DIAGNOSIS
 Histopathological changes.
 Demonstration of virus by isolation
 Embryo susceptibility test
 Laboratory tests include histopathological examination of brain,
fluorescent antibody test, ELISA, embryo susceptible test, agar-
gel-precipitation test, virus neutralization test.

15. DIFFERENTIAL DIAGNOSIS
 Newcastle Disease: sharp drop in egg production Digestive,
respiratory and nervous symptoms
 Marek’s Disease: occurs later around 2 to 3 months of age,
peripheral nerve involvement
 Vitamin A deficiency : Excessive urates in kidneys and ureters,
Pustules in mouth and pharynx, Poor growth, Poor feathering,
Nasal and ocular discharge

16. TREATMENT
 No effective treatment for the infected birds.

17. CONTROL
 Affected birds are to be segregated immediately and it is
advisable to destroy the affected birds
 Sanitation and hygienic measures are to be adopted.
 Vaccination(live vaccine) is to be done 10-16 weeks of age
,prior to egg laying.
 AE vaccine is usually combined with fowl pox vaccine and
given by wing-web inoculation.

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