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Avian Encephalomyelitis, Epidemic Tremors

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Introduction

Avian encephalomyelitis is a viral disease of the central nervous system of chickens, pheasants, turkeys, and quail. It has a worldwide distribution. Morbidity 5-60% depending on the immune status of the majority of parents, mortality high. Vertical transmission is very important, transmission occurs over about 1-2 weeks, some lateral. The route of infection is transovarian with an incubation period of 1-7 days; lateral transmission is probably by the oral route, incubation >10 days. Virus in faeces may survive 4 weeks or more.

Signs

  • Nervous signs.
  • Dull expression.
  • Ataxia and sitting on hocks.
  • Imbalance.
  • Paralysis.
  • Tremor of head, neck and wings. Tremor may be inapparent but is accentuated if chicks are held inverted in the hand.

Post-mortem lesions

  • Gross lesions are mild or absent.
  • There may be focal white areas in gizzard muscle (inconstant).
  • A few recovered birds may develop cataracts weeks after infection.
  • Microscopic - nonpurulent diffuse encephalomyelitis with perivascular cuffing.

Diagnosis

A presumptive diagnosis is based on the history, signs, and lack of significant lesions. Histopathology is usually diagnostic and IFA, and/or viral isolation may be carried out if required. The embryo protection test has been used in the past, now Elisa is used more commonly. Differentiate from Newcastle disease, vitamin deficiency (E, A, riboflavin), toxicities, EE (especially in pheasant in the Americas), Marek's disease, Mycotic Encephalitis, Brain abscess, Enterococcus hirae infection.

Treatment

None.

Prevention

Vaccination of breeders at 9-15 weeks, attenuated or not. Immunity is long lasting.