Infectious laryngotracheitis (ILT, LT, Trach)

Occurrence: Most countries. Species affected: chickens.
Age affected: All (usually older than 4 weeks).
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.

Mode of transmission

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

Clinical signs

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 signs. 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.

Postmortem lesions

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 conjunctiva and infraorbital sinuses are commonly seen.


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

Blood in the trachea is an important lesion.


Vaccinate chickens with live attenuated product by-water (embryo-derived (CEO)), spray or eye drop (cell culture derived (CEF)) at 2-4 weeks of age only in endemic areas. Revaccinate pullets at 10-14 weeks by eye drop. Revaccinate force moulted hens. The CEO vaccine virus may cause a latent infection, which can appear later causing morbidity (foamy eyes and increased mortality). The mild vaccinal form of LT is often called silent LT or almond shaped eye. New recombinant vaccine (HVT or fowl pox vector) given by in ovo to broilers or wing web stab to pullets. The vaccines work well in pullets, but their efficacy is generally not adequate for broilers.

Infectious laryngotracheitis insights

Infectious Laryngotracheitis (ILT) targets broilers

Infectious Laryngotracheitis is a viral disease most commonly found in chickens, but is also seen in other fowl. In broilers, the vast majority of outbreaks occur in flocks over 45 days of age, but the disease has been diagnosed in flocks of a younger age.