Infectious laryngotracheitis (ILT)
Infectious laryngotracheitis (ILT) is an extremely contagious virus that affects chickens and other fowl-type birds, such as turkeys and peacocks.
The virus attacks the cells of the trachea (windpipe), leading to bleeding within the trachea and the bird having difficulty breathing. Birds can die of asphyxiation when the disease is severe enough.
ILT is a nationally notifiable disease where suspicion of the disease in South Australia must be reported to PIRSA under the Livestock Act 1997.
ILT is endemic in Australia and the virus is commonly present in long-lived birds, such as egg-laying chickens. The severity of disease after infection is variable depending on the age of birds, and birds can develop natural immunity after infection. However, once birds are infected they become carriers for life and can shed the virus during periods of stress, posing a risk to young birds.
Commercial farms at risk of ILT infection routinely vaccinate their birds to minimise disease, and therefore losses, from occurring. Read more about vaccinations and antibiotics for poultry.
How ILT spreads
The virus survives well in the environment, particularly in cool, wet conditions. It is easily transmissible through physical contact or aerosol (small droplets in the breath). Aerosol spread only occurs from infected birds who are coughing large volumes of the virus into the air.
With a large population of infected birds producing a plume of virus (for example, when transporting infected birds on live-haul vehicles), and favourable environmental conditions, ILT can travel to infect other birds. It is important to consider which routes trucks should take when:
- moving uninfected birds – to minimise becoming infected from nearby infected farms
- moving infected birds – to minimise infecting nearby uninfected farms.
Spreading the virus via physical contact mostly occurs during movement of people and equipment. People on an infected farm can have their clothing contaminated with the virus, which poses a risk to birds on an uninfected farm.
Wild bird species such as pigeons and waterfowl are able to carry the virus without showing signs of disease. Therefore, contact between wild birds and poultry flocks should be minimised as much as possible.
Infectious laryngotracheitis is not a human health risk.
ILT in South Australia
An outbreak of ILT was declared in SA in September 2018 and the last associated case was notified in December 2019.
During this time there were 85 notifications of ILT, mainly affecting commercial broiler farms. All of these were the Class 7 ILT virus type, except 2 which were Class 1 – reaction to vaccinations. Over 50 of these notifications were re-infections, i.e. the same farms became re-infected with new batches of birds.
With strict biosecurity, cleaning and sanitation in all sectors of the industry, and strategic vaccination, there have been no more cases associated with this outbreak.
Since then, a few cases have been notified in the layer industry, all with the Class 7 strain. These were confined to the individual farms and were due to poor or no vaccination. These cases are a reminder of the importance of the vaccination program and correct technique.
ILT interstate
New South Wales (NSW) and Victoria have historically had greater incidence of ILT disease than South Australia. These states have also experienced more virulent classes of the ILT virus (Classes 8, 9 and 10), which occurred from mutation of the Class 7 virus.
This is why movements of birds from interstate must be carefully managed.
Reduce the risk of ILT on your farm
If your birds are showing any signs of difficulty breathing, immediately contact your local veterinarian – and you must report any suspicion of ILT infection to the Emergency Animal Disease Hotline.
Vaccination for ILT
To prevent disease from occurring, pullet farms that rear birds for commercial egg-production must routinely vaccinate all birds against ILT. This is best done by eye-drop vaccination to ensure that all birds receive the appropriate dose – as opposed to water vaccination.
PIRSA Biosecurity strongly recommends using A20 or SA2 vaccines (Class 1 ILT virus type), due to the possible nature of the Nobilis ILT vaccine (Class 7 ILT virus type) becoming associated with a disease outbreak and mutation.
It is difficult to vaccinate commercial broiler farms adequately, for these reasons:
- performing eye-drop vaccination for the large number of birds present on farms is not possible; therefore, vaccination must be done in-water
- the vaccine is fragile in the water, requiring protection from UV light and chlorine and only lasts about 4 hours
- birds cannot be managed to drink all of the water within 4 hours, but not too quickly that some get too high a dose, and others none.
Despite industry attempts, full vaccination coverage cannot be provided to the birds in commercial broiler farms. Good biosecurity is the main tool to eradicate the disease.
For more information please read about vaccinations and antibiotics for poultry.