Infectious Laryngotracheitis (ILT) is usually considered to be a backyard flock problem. However, this disease continues to plague the poultry industry with sporadic episodes across the province of Ontario. Due to the persistent, latent, infectious nature of the virus, it can perpetuate itself, even after vaccination. Rolling reaction from chicken embryo origin (CEO) vaccines and transmission from backyard flocks keeps the industry at high alert for this disease. ILT is on the list of four notifiable diseases at the request of the importing nations, China and Russia. This reminds our industry to control it now.
ILT is an acute herpes viral respiratory tract infection of chickens and pheasants that may result in severe production losses. Losses occur due to excessive mortality, decreased growth rates and decreased egg production. Disease may affect 5 to 80% of an exposed flock, taking 2 to 4 weeks to go through an entire flock. Infected birds usually die but can recover within 7 to 10 days. Mortality can climb as high as 20% in an infected flock.
Signs of infection appear 6 to 12 days after infection and are characterised by mild to severe clinical reactions. Signs include:
* conjunctivitis, watery eyes and swollen orbital sinuses.
* coughing, sneezing, extended neck, laboured, breathing, wheezing and head shaking.
* bloody exudate on the walls of cages or pens from severe cases.
Infection is usually spread by aerosol. The route of infection is through the upper respiratory tract, where the virus replicates in the trachea and the larynx. Other portals of entry include contact of the virus with the eyes and ingestion of the virus. Mechanical transmission can occur via contaminated equipment, clothing, boots, dead stock and litter.
Control focuses on management practices, emphasising strict biosecurity. Due to vaccination potential to cause disease, veterinary supervision is strongly recommended when the decision is made to go this route. Since both natural infection and vaccination have been shown to produce "carrier" birds, it is extremely important that susceptible chicken flocks are not exposed to vaccinated or previously infected chickens. Mixing of birds should only be done when a complete history of the birds is available, and it is absolutely certain that a potential ILT "carrier" is not present. Sanitation procedures, which include disinfection of equipment, boots and clothing and proper disposal of litter and carcasses, are essential components of ILT control.
It should be emphasised that it is always recommended that producers work with their poultry veterinarian for diagnosis and to develop treatment and prevention/vaccination strategies.
Submission of samples to the Animal Health Laboratory should be representative of the problem on the farm or backyard flock. Your history sheet, submitted with the birds, should include: the type of operation, the number of birds at risk, the number of birds affected and the vaccination history. Submit tissues from separate birds in tightly sealed and labelled Whirl-Pak bags for rapid distribution to the designated laboratory sections. For histology, use formalin fixed sections of trachea, larynx and bronchioles. For isolation of ILT virus, trachea and lung are required.
By Scott Gillingham - Veterinary Scientist/OMAFRA
Ministry of Agiculture, Food and Rural Affairs