B302 - AVIAN INFECTIOUS LARYNGOTRACHEITIS

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B302 - AVIAN INFECTIOUS LARYNGOTRACHEITIS

Nature of the disease
Avian Infectious Laryngotracheitis (ILT) is a disease of poultry caused by an Herpesvirus and which causes acute respiratory disease.
Classification
OIE, List B disease
Susceptible species
Chicken, turkeys, pheasant and peacock.
Distribution
ILT is worldwide distributed. In the Pacific Region it is reported in Australia, Guam and New Zealand, serologic evidence have been found in Cook Islands, Kiribati, Tonga, and Wallis and Futuna.
Clinical signs 
Incubation period ranges from 5 to 10 days. Severity may vary accordingly to the strain of virus.

In the acute form symptoms include:

  • Rhinitis,
  • Swollen head (oedema),
  • Breathing difficulty,
  • Drop in productivity,
  • Loss of appetite,
  • Haemorrhagic tracheal exudate that may recover the beak, 
  • Sometimes pneumonia or broncho-pneumonia
  • Mortality reaches 50%. Animals recover after 2-4 weeks.

The subacute form causes mild respiratory symptoms (coughing and gasping) and reduced productivity. Mortality approximates 15%. Mild ILT may extend over months with deaths occurring at irregular intervals. 

Post-mortem findings 
In the acute form post-mortem lesions are limited to the upper respiratory tract and consist of haemorrhagic tracheitis with blood clots and blood-stained mucus along the length of the trachea. 

In the subacute form lesions consist of mucoid exudate with or without blood in the trachea. Yellow caseous diphtheritic membranes may be found adherent to the larynx and upper tracheal mucosa.

Differential diagnosis 
Specimens required for diagnosis 
Best specimen for identification of the virus are tracheal exudate and tracheal tissue samples, techniques include direct electron microscopy, immunofluorescence, agar gel immunodiffusion (AGID) and an enzyme-linked immunosorbent assay (ELISA) to demonstrate viral antigen in mucosal scrapings. PCR is also available.

Serological methods include virus neutralisation test, AGID, indirect immunofluorescence, or ELISA.

Transmission   
ILT is very contagious and transmission occurs by contact with respiratory droplets, infected feed, husbandry materials.

Sub clinically infected animals carry the disease for months and are often the cause of introduction of the disease.

Risk of introduction   
ILT could be introduced by importation of subclinically infected animals. OIE also considers hatching eggs and day-old chicken.
Control / vaccines  
Vaccines based on live attenuated virus are available but are not completely satisfactory.

Control of ILT is difficult and isolation of flocks should be considered with testing of introduced animals.

References
  • Infectious Laryngotracheitis, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p. 1982-1983
  • Office International des Epizooties, 2002
  • Office Vétérinaire Fédéral Suisse
  • SAVILLE P. South Pacific Commission, Infectious Bronchitis and Infectious Laryngotracheitis, Animal Health Advisory Leaflet 4, Noumea 1996