39. Avian encephalomyelitis.

Question 1

Occurrence and aetiology?

Answer 1

Occurrence

• 1932 USA
• Worldwide, widespread infection
• 1968 Hungary
• Clinical form is not common

Etiology

• Avian encephalomyelitis virus
• Tremovirus genus
• 1 serotype
• High resistance ➝ infective for several months

Question 2

Epidemiology?

Answer 2

Epidemiology

• Chicken, pheasant, turkey, quail susceptible
• All age groups are susceptible to infection
• Maternal protection lasts 3-6 weeks
• Clinical signs mainly in 1-2 week old, up to 4-5 weeks of age
• Spread
- Germinative ➝ infected eggs for 3 weeks after infection
- Faeces ➝ shedding for several weeks
- Fast spread within flock
• Morbidity: 50-60%
• High lethality

Question 3

Pathogenesis?

Answer 3

Pathogenesis:

Pathogenesis

1. Per os infection, mucous membrane of gut
2. Viraemia
   - Pancreas, liver, spleen, kidney, ovarian ➝ does not kill embryo
   - Central nervous system (CNS) ➝ inflammation, necrosis
3. Shed in faeces ➝ horizontal infection
4. Good immunity and maternal protection

Question 4

Clinical signs?

Answer 4

Clinical signs

• Incubation: 1-11 days
• Chicken
- Nervous signs
- No eating, drinking, diarrhoea, opacity of lens, iridocyclitis, death
• Older animal
- Subclinical
- Egg production drops by 5-10%

Question 5

Pathology and histopath?

Answer 5

Pathology

• No gross pathologic lesions

• Histopathology

• Central nervous system (CNS), grey matter ➝ cerebellum, brain stem, spinal ord
• Lymphocytic infiltration
• Regeneration of neurons
• Glia replication

Question 6

Diagnosis?

Answer 6

Diagnosis

• Epidemiology ʹ clinical signs, histology
• Detection of the virus: PCR, IF, isolation of the virus
• Detection of the Abs: AGID, VN, ELISA (quite reliable)

Question 7

Differential diagnosis?

Answer 7

Differential diagnosis:

1. NDV (CNS, resp, diarrhoea, haemorrhage),
2. Avian influenza, Marek disease,
3. encephalomalatia

Question 8

Prevention?

Answer 8

Prevention

• General epidemiological methods
• In case of fresh infection hatching for 1 month is not allowed
• Vaccination with live vaccine in drinking water (retained virulence, isolation of animals!) ʹ
• vaccinate 4-5 weeks before the laying period
• Layers have to be vaccinated 1 month before laying
• Virus shed, 5-10% of the animals are vaccinated in the flock ʹ spread