Infectious laryngotracheitis

General description and impact

Infectious laryngotracheitis (ILT) is a severe contagious disease caused by a virus affecting the respiratory system of chickens (Gallus gallus). This includes commercial layers and breeding layers; but it can also affect other species such as partridges, pheasants and peacocks.

In chickens, the disease can affect birds of any age and stage of production, but the most characteristic clinical signs are observed in birds over 3 weeks of age until adulthood. The incubation period for the disease is usually 6 to 12 days. It is a disease which mainly causes mortality and growth retardation without condemnation in broiler chickens. Weight gain may be delayed by 2 to 5 days in broiler chickens. Mortality is generally between 10 and 20%. The illness may persist for a period of 2 to 6 weeks.

Source and spread of infection

ITL can be spread by contact with infected birds but is mainly transmitted indirectly through contaminated objects (vehicles, litter, transport cages, feathers, carcasses, etc.), people (boots, clothing, contaminated hands), wild or domestic animals, rodents and insects (e.g. mealworms). There have also been reports of infection caused by biosafety breaches during the use of live attenuated vaccine or poor vaccine administration technique in some cases.

Clinical signs

In addition to increased mortality, the signs are mainly those of a serious respiratory illness. For example: difficulty breathing; very noisy breathing; breathing while stretching the head and neck; shaking the head (to expel mucus and blood from the airways); bloodstains on beak and feathers. In addition to respiratory symptoms, affected flocks may also show: a reduction in feed and water consumption; a decrease in egg production; birds tending to huddle together, less active, feathers are ruffled; conjunctivitis (red, watery eyes).

Number of outbreaks and diagnosed cases of ITL from 1999 to 2023