Avian Encephalomyelitis (Epidemic Tremor)
Avian Encephalomyelitis also known as Epidemic tremor.
Avian Encephalomyelitis (Epidemic Tremor) is an acute viral disease of very young chickens (1-21 days) characterized by ataxia, paralysis, tremors in head and neck.
Etiology
- Avian Encephalomyelitis (Epidemic Tremor) is caused by genus Enterovirus in the family Picornaviridae, a single stranded RNA virus.
- The virus is susceptible formaldehyde fumigation and inactivation with ß- Propiolactone.
- There are two distinct pathotypes of virus namely field strain (enterotropic) and shed in faeces, embryo adopted strain is highly neurotropic and causes severe neurological signs.
Host affected
- Chicken, turkeys, Japanese quail, pheasants and pigeon.
- Morbidity rate: 40-60% and Mortality rate: 25% and may exceed 50%.
Source of infection
- The very young chicks excrete the virus through faeces for more than two weeks.
Transmission
- Vertical transmission.
- Horizontal transmission (Ingestion is the portal of entry of virus).
Clinical manifestation
- Dull expression of eyes.
- Progressive ataxia from incoordination of muscle.
- Sit on their hocks, lateral recumbency, fine tremor of head and neck.
- Chicks with marked ataxia and prostration are frequently trampled by their penmates.
- Reduced egg production and hatchability.
- Opacity of lens, either unilateral or bilateral.
- Nervous signs may seen at or soon after hatching, but most commonly at 1 week of age.
Pigeon
- Paralysis of the wings, opisthotonus, torticollisis and head tremor
- Diarrhoea
Necropsy Findings
- Whitish area in the muscularis of ventriculus (due to mass of infiltration of lymphocytes.
- CNS- disseminated non-suppurative encephalomyelitis, perivascular infiltrate in all portion of brain and spinal cord are seen.
Sample collection
- Brain, pancreas and duodenum.
Diagnosis
- Isolation of virus by inoculation of tissue homogenate in yolk sac route 5-7 days of embryonated egg- muscular dystrophy is evident in embryo.
- Nested PCR is used to detect viral antigen in clinical sample.
- VNT and ELISA are used for detection of antibodies in serum.
Control
- Live and inactivated vaccines are available.
- The live vaccine most commonly used, this given in drinking water.
- Vaccination by wing web inoculation of AEV practiced, but this some risk of causing clinical disease.
- Generally vaccination is done after 8 weeks of age and atleast 4 weeks before egg production.
