28. Infectious laryngotracheitis of chicken.

Question 1

History, Causative agent?

Answer 1

Infectious laryngotracheitis (ILT) of poultry ʹ upper resp tract illness & conjunctivitis of mainly chickens

History,

• occurrence: first description ʹ USA,
• 1925; Viral origin (1930),
• the 1st poultry vaccine (1932),
• worldwide distribution

Causative agent:

• GaHV-1, Alphaherpesvirinae, Iltovirus
• Propagation in CAM, in chicken cell cultures
• 1 serotype, several virulence variants
• Chicken, pheasant, turkey, peacock, quail susceptible (mostly chicken)

Question 2

Epizootiology, pathogenesis?

Answer 2

Epizootiology, pathogenesis

• Air-borne infection: upper airways, conjunctiva (NOT in bronchi & parenchyma of lungs)
• Local multiplication: no viraemia!
• No germinative infection
• Convalescent birds are long-term carriers & shedders
• Very contagious: quick spread in the population
• Virus multiplication in the mucosa of the upper third of the resp tract epithel & endothel damage,
• exudates, oedema, haemorrhages

Question 3

Clinical signs?

Answer 3

Clinical signs:

• mainly in growers & adults
• Incubation: 6-12 days (2-4 days) : severity depends on the virulence of the strain & the immunity of the host
• Typical form: (virulent virus): Don’t say coughing/sneezing birds die because they can’t cough-> suffocate!)
• Dyspnoea (gasping), rattling, extension of the neck during inspiration
• The mouth & beak may be blood-stained from the tracheal exudate
• Eyelid oedema, conjunctivitis, haemorrhages, exudate
• Shady cornea, ulceration, uveitis, fibrin precipitation, almond-shape eyes
• Reduced egg production
• Anorectic, inactive birds
• Haemorrhage & fibrin precipitation in the trachea ʹ cheesy plugs ʹ occlusion
• Mortality in adults 10-20 (50-70)%, recovery w/in 2-6 weeks
• Mild form (low virulence strains):
• Conjunctivitis, swollen sinuses, nasal discharge
• Mortality ~ 5%
• Production loss (layers, broilers)
• Secondary bact infections (Ornithobacterium rhinotracheal, E. coli, Mycoplasma)
• Necrotising MM inflammation
• formation of pseudomembranes is typical form fibrinous plaque
• which gets into the pharynx & obturating it-> chicken cant’t get cough so remove the plug
• (suffocate)

Question 4

Pathology/histopathology?

Answer 4

Pathology, histopathology

• Trachea mucosa swollen, red, bleeding, pseudomembrane, cheesy plug
• Desquamative,
• necrotising tracheitis:
• cilia disappear,
• cellular infiltration, degeneration of the
• capillary walls,
• nuclear inclusion bodies

Question 5

Diagnosis?

Answer 5

Diagnosis

• Typical -signs, pathology findings
• Mild ʹ lab confirmation necessary
• Isolation, IF, PCR, in situ hybridisation

Question 6

Differential diagnosis?

Answer 6

Differential diagnosis:

1. Newcastle disease: enteric haemorrhage, CNS
2. Avian influenza
3. Mycoplasmosis: chronic, inflammation of airsacs
4. Infectious bronchitis: younger chicken, oviduct involved, no fibrin precipitates, gout
5. Swollen head syndrome (Metapneumovirus): milder tracheal lesions, egg deformities
6. (Fowlpox : proliferative tracheal lesions)

Question 7

Prevention?

Answer 7

Prevention

• Sporadic: slaughtering and replacement
• Epizootic: immunisation
• Eye drop w/ attenuated vaccine (Drinking, aerosol is less efficient)
• Broilers: in the 2-4 weeks
• Layers: week 4 & week 12-16 ʹ protected for 1 laying period
• Attenuated vaccines are shed by the birds
• Fowlpox vectored ILT vaccine are also marketed