Guide to managing infectious laryngotracheitis in poultry

Infectious laryngotracheitis (ILT) is a respiratory disease caused by the virus Gallid herpesvirus type one (GAHV-1).

Within the commercial production of broilers and layers, naive birds – those that have either not been vaccinated or exposed to wild virus – are most vulnerable.

Aonghus Lane (right), regional lead vet for Ireland at St David’s Poultry Team, explains what the risks are with ILT and why poultry producers need to stay ahead of the game.

See also: Expert tips to reduce poultry vet and medicine costs

What is the risk for producers?

ILT can be found across the world, and it is endemic in the UK. While it is not a notifiable disease in Great Britain, it is in Northern Ireland and the Republic of Ireland.

Cases that look suspicious or are confirmed must be reported to the Department of Agriculture, Environment and Rural Affairs (Daera) or Department of Agriculture, Food and the Marine, in Northern Ireland and the Republic of Ireland, respectively.

Although there are no mandatory restrictions or actions at flock level, the reporting mechanism recognises the severe implications an outbreak can have.

What is the impact on production?

The disease has high infection rates, typically affecting between 50% and 100% of flocks, and the associated respiratory distress significantly compromises welfare.

Production is heavily affected – in layers, egg production can fall by up to 30% and, in broilers, average daily weight gains can suffer. This has big economic consequences for the business.

Mortality varies widely with mild clinical disease ranges between 0.1% and 2%, and severe, acute disease up to 70%.

Daera puts typical mortality at 10-20%, but overall mortality is heavily influenced by the particular strain of ILT.

Once infected, a bird is a lifelong carrier. These so-called “latent” birds are susceptible to repeat waves of disease throughout their lifetime – triggered by environmental, physiological, and management stressors.

They also shed the virus, sometimes in the absence of clinical signs, and represent a persistent source of potential infection to birds on the affected and nearby farms.

What are the clinical signs of ILT?

Manifesting as an upper respiratory tract infection, it causes inflammation of the larynx, trachea, and conjunctiva (eyelids).

Clinical signs and severity will depend on the strain of the virus, the age of the birds, and the presence of other diseases such as infectious bronchitis.

Early signs are usually noticeable five to 12 days after infection, and include:

• discharge from the eyes
• conjunctivitis
• snicking, sneezing, squawking
• reduced feed and water intake.

Moderate and severe disease sees worsening clinical signs:

• swollen eyes
• a cough
• rales in the lungs.

Respiratory sounds are best heard after lights have gone out, which makes abnormal sounds more noticeable. Birds may also have bloodstained beaks and stained feathers from rubbing.

Severe cases can present as an outstretched neck and gasping. Asphyxiation from inflammation causing respiratory obstruction can cause sudden death.

How is ILT diagnosed?

It’s important to differentiate ILT from other respiratory diseases that could be present, from both a treatment and regulation perspective.

Vets can carry out throat swabs on live birds for PCR testing and virus isolation; the latter allows them to identify which strain of ILT is present and decide on courses of action.

Dead birds can be presented for post-mortem examination and samples taken for analysis.

Farmers need to consult with their vet and must not take suspected cases directly to the practice.

How is it transmitted?

ILT can quickly spread through a flock and if biosecurity practices are poor, it can be easily transmitted from one house to another.

Transmission between farms can occur via airborne particles, birds and feather debris, as well as vehicles, clothing and equipment.

Wind-borne transmission can also be an issue when contaminated poultry litter is transported or stored unsealed. Spreading contaminated litter also increases risk.

The disease primarily spreads through bird-to-bird contact. Discharge from the eyes and respiratory tract have the highest viral loads; ILT is also shed in faeces.

The virus can survive in warm, damp litter for 21-28 days, and for 10 days to three months in chicken respiratory exudes and carcasses.

It will also populate biofilms in drinking water lines. ILT cannot be transmitted to humans and poses no food safety risk.

How is ILT treated?

There is no medical treatment for ILT. However, birds can be nursed through episodes by optimising their environment and ensuring they have resources easily available.

This will help birds recover more quickly. Incorporating nutraceuticals will also help to stimulate appetite and drinking while providing supplementary energy and vitamins.

In cases of moderate and severe disease, humane culling may be necessary.

At turnaround, deep cleaning of the house and all equipment is essential, replacing personal protective equipment, where necessary, to prevent infection of subsequent flocks.

ILT is easily killed by disinfectant, which provides very effective control when used in the right way, at the correct dilution, usage rates and application methods.

Fumigation is strongly recommended, as is thorough disinfection of drinking lines; producers could also consider installing autoflush systems.

Weighing up the costs

The cost of infectious laryngotracheitis  is hugely variable.

It’s entirely dependent on the strain of virus, management of the birds, other diseases, and challenges present, as well as industry prices at the time.

Other costs include implementing enhanced biosecurity, the interruption of bird movement, and litter management both in and away from the house.

The vaccine is relatively inexpensive – about 6.5p a bird – but that doesn’t account for the cost of time and labour associated with vaccination.