Infectious laryngotracheitis

Description

Infectious laryngotracheitis (ILT) is a viral respiratory disease caused by Gallid herpesvirus 1 (GaHV-1). This disease is highly contagious and spreads either by direct contact with infected birds or indirectly by people and contaminated materials. Two important factors contribute to the spread of ILT in poultry flocks:

• mixing of birds from various sources
• inadequate biosecurity

Both severe and mild forms of the disease are possible in poultry flocks at the same time, commonly affecting:

• chickens
• pheasants and pheasant-crosses
• peafowls

Less commonly affected are turkeys, partridges, grouse and guinea fowl.

The percentage of birds in the flock affected by this disease can vary from 5 to 100%. Mortality varies from no death loss to 20% or more. The infection can cause illness in birds lasting from days to weeks, and predispose the birds to other respiratory pathogens. It is possible to see both severely and mildly affected birds in the same flock at the same time.

Milder disease may occur due to exposure to certain ILT vaccine strains that revert to virulence, or due to less virulent field viral strains. Milder cases may also indicate previous exposure of the flock to the virus. As a result, some birds may have enough immunity to protect them from clinical disease or reduce the severity of the signs.

Most species of wild birds, including crows, sparrows and pigeons, and pet birds including canaries and budgerigars are resistant to infection with ILT virus but may still spread it.

There is no evidence to suggest that ILT virus is transmissible to humans or other mammals.

How to report

All suspected or confirmed cases must be reported to the Office of the Chief Provincial Veterinarian (OCPV) within 24 hours:

Hours: 8:15 am to 4:30 pm (open Monday to Friday, closed statutory holidays)
Phone: 780-427-3448
Toll free: 310-0000 before the phone number (in Alberta)
Fax: 780-415-0810

Clinical signs

Although ILT affects all ages of poultry, the most characteristic signs of the disease can be observed as early as 3 weeks of age. The ILT virus can affect the larynx, trachea (windpipe), lungs, nasal sinuses and conjunctiva (mucus membrane lining of eyelids).

The clinical signs of ILT are very similar to other viral infections of poultry such as avian influenza, Newcastle disease and infectious bronchitis. In suspect cases, until a diagnosis is made, it is important to contact your veterinarian or the OCPV and to stop all movements of birds and potentially contaminated tools or equipment in and out of the premises.

Clinical signs generally appear 6 to 14 days following exposure and vary depending on the strain of the virus and severity of the infection. Signs of ILT can include:

• depression
• reduction in feed consumption
• sudden drop in egg production
• sneezing
• swelling of eyelids and face
• discharges from the nose or eyes
• coughing
• gurgling sounds (rales) and coughing blood or blood-stained mucus
• difficulty breathing (gasping for air with neck extension and open-beak breathing) due to obstruction of trachea and larynx
• increase in flock mortality

Where it’s found

Rare in commercial poultry operations in Alberta, ILT is more common in hobby or fancy poultry flocks. Adequate biosecurity is difficult in flock operations that add new birds from various sources on an ongoing basis.

How it spreads

Introduction of an infected (carrier) bird into the flock is the most common method of spread. Transmission of ILT between infected and susceptible birds occurs through nasal, ocular (eye) and oral routes. Aerosols from infected birds can travel over short distances (1 to 2 meters) and potentially farther. Although highly contagious, the virus normally travels slowly through flocks housed in separate cages, coops or runs. Transmission is also possible via contaminated objects such as people, footwear, vehicles and equipment. Contamination of eggshells with ILT virus may occur if laying birds are infected.

Birds recover from illness in approximately 10 to 21 days but will carry the virus for the rest of their life, becoming carriers. If stressed – such as at the onset of laying, during inclement weather, after new flock introductions, caused by nutritional deficiencies or other diseases – carrier birds can shed the virus and infect susceptible birds. These chronically infected carrier birds may appear healthy yet still be a source of the virus. Vaccinated birds may also shed the virus later in life or be susceptible to different viral ILT strains, showing milder to no upper respiratory symptoms.

The ILT virus can survive in the environment for variable lengths of time depending on ambient temperature (for example, warmer temperatures reduce survivability). Susceptible birds placed in a contaminated environment are at risk of ILT.

Although resistant to infection with ILT virus, wild birds, rodents, and pets may still spread it by carrying it on their body. Waterfowl (ducks and geese) show no signs, but ducks have been known to carry ILT for up to 2 weeks.

Risk to humans

As there is no evidence to suggest that ILT virus is transmissible to humans or other mammals, there is no human health or food safety risk associated with the virus.

Prevention and control

The most effective ways to prevent and control ILT outbreaks are:

• good management
• rapid diagnosis
• preventing further spread by practicing proper biosecurity
• implementing a vaccination program for all susceptible birds

Management best practices

An effective biosecurity plan is essential to prevent the introduction of infectious diseases like ILT into a flock. Continuous evaluation of biosecurity procedures is important. Commitment, dedication and persistence by all farm staff including owners and visitors is required for successful implementation of biosecurity.

The key elements of an ILT biosecurity strategy include:

• Maintain a closed flock (no additions from other flocks) or only purchase birds from a reliable source known to be free of ILT.
• Introduce eggs or day-old chicks instead of adult birds to add new genetics to your flock. Remember, adult birds can be infected with and shed ILT virus while appearing healthy.
• If you purchase birds or have birds returned from shows/exhibitions, isolate (quarantine) them away from your resident flock for a minimum of 21 days before mixing with your resident birds. During this time, they should be monitored for any signs of illness.
• Strict biosecurity procedures should be in place to prevent any illnesses from spreading to your birds:
  • Do not allow other people to enter your barns, especially if they have contact with other poultry.
  • Use designated footwear if you choose to visit other poultry farms or barns.
  • Provide clean footwear for everyone who enters your barn or bird-holding areas.
  • Always wash your hands before and after handling the birds or their environment.
  • Restrict vehicle traffic to specific areas away from your birds.
  • Restrict the access of other animals (such as dogs, cats, rodents, wild birds) to your poultry barns.
  • Prevent contamination of feed and water sources.
  • Store carcasses in a closed container until they can be disposed of according to the requirements of the Disposal of Dead Animals Regulation. Confirm with your local authorities regarding appropriate carcass disposal (for example, incineration, burial, composting.
  • Employees of commercial poultry farms should not own poultry or fancy birds to prevent spread of infectious diseases from birds at home.
  • Perform a thorough cleanout and disinfection, followed by a minimum of 4 weeks downtime, between flocks to avoid carryover between the successive flocks.

For more information see:

• Cleaning and disinfecting backyard poultry flock premises
• Resources for poultry owners
• National Avian On-Farm Biosecurity Standard

Diagnosis

Because no test can reliably detect ILT in a healthy carrier bird, there is no way to determine if a symptom-free flock or bird is carrying the virus.

Consult a veterinarian as soon as clinical signs are observed to determine the cause of illness or death in your flock. ILT can be confirmed by examination of the dead birds and by specific laboratory tests through Alberta’s small-flock disease investigation program.

Vaccination

In consultation with your veterinarian, conduct a risk assessment for your flock to determine if vaccination against ILT is deemed necessary.

Three types of ILT vaccines are available:

1. Tissue culture origin (TCO) vaccine – (most recommended) is administered as an eye drop to each chicken 4 weeks of age or older. This vaccine can be administered during an ILT outbreak to help reduce shedding of the virus. This live virus vaccine is unlikely to revert to virulence and is the one currently recommended in Alberta.
2. Recombinant vector (rILT) vaccines – may be administered at the hatchery in ovo (18-day-old embryos) or to day-old chicks. This vaccine may also contain protection against Marek’s Disease or Fowlpox. rILT vaccine virus is not shed; therefore, unvaccinated birds are not at risk when exposed to birds vaccinated with this vaccine. Contact your hatchery for more information.
3. Chick embryo origin (CEO) vaccine – strongly discouraged because this vaccine virus can revert to virulence and cause severe disease in vaccinated and unvaccinated birds.

Important to know

• Vaccinated birds can still shed the virus. Any new bird introduced into an ILT vaccinated flock should also be vaccinated.
• Vaccinating sick birds during an ILT outbreak helps reduce viral shedding, decreasing contamination of the environment with the ILT virus.
• ILT vaccines should only be used under veterinary guidance and according to manufacturer’s directions.
• Incorrect use of ILT live vaccines can lead to the emergence of virulent ILT strains responsible for severe outbreaks of the disease.

Treatment

There is no specific treatment for ILT. Affected flocks should be provided with clean water, high quality feed, good ventilation and a comfortable environment to aid in their recovery. Treatment with antibiotics is not effective because ILT is a viral infection. Your flock veterinarian may prescribe antibiotics to help prevent secondary bacterial infections. Although vaccines are available, early slaughter or depopulation of the ILT-infected flock is in some cases the best solution to prevent the spread of the disease.

Alberta’s response to ILT cases

The diagnosis of ILT in a flock initiates notification to:

• poultry boards
• hatcheries
• feed companies
• producers registered in the Premises Identification System (PID) whose flocks are located within 20 km of the positive flock

Notifications do not include confidential information, such as the exact location of the outbreak and producer information. They simply serve as a reminder to producers and industry to enhance the biosecurity of their flocks and to report any suspicious losses to the OCPV.

In June of 2018, the Alberta government changed the way it responds to ILT positive cases in small poultry flocks. Under the new policy, quarantine and a farm visit by Alberta government staff no longer occurs for ILT positive farms. Alberta government staff continue to provide a telephone consultation about the disease, options to manage the disease, and biosecurity advice. The Alberta government tracks and publishes quarterly confirmed cases of reportable and notifiable livestock diseases, including ILT.

Flock owners are encouraged to work with a private veterinarian for continuing disease management to ensure flock health and welfare.