Occurrence: Most countries.   Species affected: chickens.   Age affected: All ages.

Causes: Laryngotracheitis virus is a cuboidal, enveloped DNA herpes virus.

Effects: The virus has an incubation period of 6-12 days. Different pathotypes have differing pathogenicity. Morbidity is 90-100%. Mortality ranges from 5-70% (average 10-20%). In layers there is a drop in egg production. Early sign is watery eyes, followed by nasal discharge, gasping, tracheal rales and stretching necks. Slinging away the blood from the nose causes blood stains to be seen along the sides of the walls.

ILT is mainly acute to chronic and affects all birds, though usually those older than 4 weeks. The herpes virus is a cuboidal, enveloped DNA virus.

Older carrier birds are a common source of infection. Aerosol, fomites, ingestion of contaminated litter are also common means for viral spread.

An incubation period of 6-12 days. There are many pathotypes of the virus. Some are very mild and others can cause severe morbidity and mortality.

Mortality (average 10-20%, range 5-70%), morbidity (90-100%), drop in egg production (10-20%), watery eyes early on, then nasal discharge, gasping, tracheal rales and stretching necks are common sings. Slinging of blood from nose causes blood stains along the sides of walls.

Most birds recover in 10-14 days if infection is not complicated by immunosuppression or a secondary bacterial or mycoplasma infection.

Mucous in trachea is seen first, followed later by necrotic tissue, then blood. Inflammation of bronchi and lungs, foamy air sacs, oedema and congestion of the conjuctive and infraorbital sinuses are commonly seen.

Laboratory tests include microscopic observation of intranuclear inclusion bodies in the lesions (usually trachea).

Blood in the trachea is a important lesion.

Vaccinate chickens with live attenuated product by-water (embryo-drived), spray or eyedrop (cell culture derived) at 2-4 weeks of age only in endemic areas. Broilers are rarely vaccinated for ILT.

Revaccination of pullets at 10-14 weeks by eyedrop. Revaccinate force moulted hens.

Antibiotics for secondary invaders are helpful. Vaccinate only in endemic areas and quarantine all affected flocks.

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