Aetiology
This is caused by RNA virus commonly known as enterovirus belonging to picornaviridae.
Host range
The disease is mainly a disease of many fowls but may occur infrequently in turkey, pheasants and guinea fowls.
Transmission
The mode of transmission is primarily vertical through the egg but also horizontal by ingestion of contaminated feed and water.
Source of infection include carrier adult, egg and actively infected chickens. The faeces from carrier and clinically affected chicks served as source of infection.
Clinical signs
In vertical infected chicks, incubation period is 2-3 days or longer but when there is horizontal transmission between chicks, incubation period is about 2 weeks. The early stage of the disease starts with dullness of the eyes followed by progressive ataxia and muscular incordination. In severely affected birds, there is reluctance to move or when forced to move, they present a shaky gait or crawl on their hocks and shanks. In advanced cases, tremor occurs in affected chicks. Mortality may occur for two reasons such as starvation due to inability to reach feed and water and trampling over by other chicks. In the later stages when most of the clinical signs are subsided, survivors may present with corneal opacity and blindness. The disease is in-apparent in adult birds except for a temporary drop in egg production. The disease is much milder in chicks than turkeys.
Post-mortem lesions
There is no gross detective lesion in avian encephalomyelitis. In the brain and spinal cord, lesions observed are disseminated non-purulent encephalomyelitis and ganglionitis.
Diagnosis
A tentative diagnosis is reached by considering the age of birds, clinical signs, absence of appreciable gross lesions which can be strengthened by histology.
A definitive diagnosis is based on isolation and recognition of the virus.
Control
The control can be achieved by management and hygienic practice which minimize infections by horizontal means.
Ensure that chicks are sourced from disease free breeder flocks.
Vaccines are available but usually targeted at breeder stock on which they are applied before the onset of egg production usually at 12-16 weeks of age.
Progeny from vaccinated birds or naturally infected flocks retain antibodies for about 8 weeks and should not be vaccinated before 10 weeks of age.