By Dr. Maral Rahmani
PoultryMed Veterinary Services
March 2025
Introduction
Infectious laryngotracheitis (ILT) is a highly contagious respiratory disease affecting chickens and some gallinaceous birds such as pheasants and peafowl (but not turkeys). Caused by a herpesvirus, ILT has been an ongoing concern in poultry-dense regions like the Fraser Valley, BC, where it remains a reportable disease.
Why is ILT a Major Concern?
ILT is particularly problematic in areas with high poultry density and multi-age flocks, where both wild-type and vaccine virus strains can spread rapidly. The persistence of the virus is often due to:
- Inconsistent biosecurity practices
- Poor communication within the industry
- Failure to follow disease control protocols
Without strict preventive measures, ILT outbreaks can cause significant economic losses, impacting flock health, egg production, and overall farm productivity.
Transmission
ILT spreads through respiratory secretions, entering birds via the upper respiratory tract or eyes. The virus can be inhaled or transmitted through contaminated equipment, clothing, and people handling birds. It has been detected in dust up to 500 meters from infected barns. Once introduced, ILT spreads primarily bird-to-bird, with acutely infected birds shedding the virus more readily. Multi-age farms pose a higher risk of transmission from older to younger flocks. ILT-infected flocks are considered lifelong carriers of the virus and can serve as a source of future infections for other flocks.
Clinical Signs
ILT symptoms vary based on the virus strain and infection severity, but common signs include:
- Gasping and difficulty breathing (dyspnea)
- Ocular discharge and sinusitis
- Frothy eye
- Nasal discharge (common with less severe strains)
- Reduced egg production
- Coughing up mucus or blood (in severe cases)
Figure 1: Frothy eye – Photo by Dr. Maral Rahmani
Post-mortem Lesions
Upon necropsy, ILT often presents as:
- Swelling of the conjunctiva and infraorbital sinuses in mild cases of ILT
- Hemorrhagic inflammation of the trachea and the presence of bloody mucoid casts in severe cases
Figure 2: Hemorrhages in trachea – Photo by Dr. Maral Rahmani
How is ILT Diagnosed?
While presumptive diagnosis can be made based on clinical signs and lesions, a definitive diagnosis requires microscopic examination of the trachea and conjunctiva from affected birds.
Strategies for ILT Prevention and Control
1. Vaccination
While ILT vaccines do not prevent infection, they help reduce disease severity and economic impact, especially in areas where the disease is endemic. The most common used vaccines in Canada are:
- Recombinant ILT vaccines, given at the hatchery, help reduce clinical signs and maintain bird performance but are less effective at limiting virus shedding.
- Live attenuated TCO vaccines provide stronger protection against respiratory symptoms and mortality, while also reducing virus replication and shedding. TCO vaccines are highly attenuated, ensuring strong immunity without regaining virulence or spreading between birds
2. Biosecurity and Farm Management
- Strict biosecurity measures are essential in stopping ILT transmission. Key practices include:
Sanitizing equipment, vehicles, and personnel to prevent virus introduction - Controlled movement of people and birds to limit disease spread
- Thorough cleaning and disinfection of barns after flock shipment
- Extended downtime before next placement to break the virus cycle
- All-in/all-out operation
Final Thoughts
ILT remains a serious challenge for poultry producers, but a proactive approach combining vaccination, biosecurity, and effective farm management can significantly reduce its impact. Educating poultry farmers and ensuring compliance with disease control protocols are key to keeping flocks healthy and minimizing industry losses.
Important: ILT is a reportable disease in British Columbia. If you suspect ILT in your flock, immediately self-quarantine the premises and contact your veterinarian for guidance and testing.
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References
Chin, R.P. et al. Intervention Strategies for Laryngotracheitis: Impact of Extended Downtime and Enhanced Biosecurity Auditing. Avian Diseases. 2009; 53:574-577.
Guy, James S. and Trevor J. Bagust. Chapter 4: Laryngotracheitis. Diseases of Poultry. 13th edition. Ames: Wiley-Blackwell, 2013. Print.
Dufour-Zavala, Louise. Epizootiology of Infectious Laryngotracheitis and Presentation of an Industry Control Program. Avian Diseases. 2008; 52:1-7.
Volkova, Victoriya et al. Factors Associated with Introduction of Infectious Laryngotracheitis Virus on Broiler Farms During a Localized Outbreak. Avian Diseases. 2012; 56: 521-528.
