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.