Understanding infectious laryngotracheitis
Respiratory disease leads to severe losses
Responsible for major losses in the poultry industry, Infectious Laryngotracheitis or ILT is an acute respiratory disease caused by a herpes virus. Although people are not affected by ILT and because cooking destroys the virus, it is safe to eat poultry products from infected birds. But the most serious threat is to the flock itself - with deadly outcomes.
ILT usually kills between 10% and 20% of infected birds, although mortality can run as high as 70% in some cases. It is found in most areas where chickens are raised. Infected chickens serve as the primary source of infection when they shed the virus and transmit it to other chickens through respiratory secretions, and from coughing and sneezing.
People who work with Ilt-infected poultry can spread the virus through contaminated hands, footwear, clothing, equipment, vehicles, litter, and other mechanical vectors. Improperly disposed chickens that die from ILT can serve as a source of infection, especially through scavengers like domestic dogs and wild animals. Recovered and vaccinated chickens can also serve as carriers of ILT and can shed the virus when they are subjected to stressful conditions.
Clinical signs (as described below) usually appear 6 to 12 days after exposure to ILT virus. This time interval is called the incubation period and will vary according to the amount of virus and other factors such as the immune status of the chicken, environmental conditions (such as high levels of dust and ammonia), and concurrent infection with other bacteria and viruses.
Chickens suffering from a mild form of ILT usually have swollen, watery eyes (conjunctivitis), swollen sinuses, and a persistent watery or mucoid nasal discharge (Figure 1). These clinical signs are similar to other respiratory diseases of poultry. Chickens with a severe form of ILT exhibit labored, open-mouth breathing (Figure 2), frequent sneezing, and violent coughing, often accompanied by bloody mucus. These chickens will usually shake their heads to clear the mucus from their nose and mouth, resulting in bloodstained mucus on their feathers and on the walls of the chicken house or shed.
Running the course
The course of the disease ranges from 10 to 14 days but depends largely on the severity of clinical signs and lesions. Chickens that exhibit open-mouth breathing and coughing of bloody mucus usually die within a few days, but those with mild clinical signs are more likely to recover.
The severity of the clinical signs and lesions is related to the mortality seen in flocks with ILT. Mild forms of the disease result in very low morality (0.1-2%). Severe forms of the disease result in variable mortality (5-70%), with the average being 10-20%.
In ILT infections, clinical signs alone should make you highly suspicious. Even so, as with any disease, you should submit birds to the diagnostic laboratory in your area for confirmation of the diagnosis. A post-mortem examination of affected birds will generally reveal blood in the bird’s airway. The trachea or windpipe is often very bloody and may be partially clogged with mucus and blood (Figure 3). Swabs of the trachea will be used to attempt to grow the virus. Other diagnostic tests may be performed to confirm that your flock has ILT.
Protecting the flock
There are different types of vaccines that can be used to control ILT. Owners should consider the tissue culture origin (TCO) vaccine, which is administered by simple eye drop. Administration of this vaccine should occur at least 30 days prior to shows and fairs. As with all available vaccines, the labeled directions for use and administration must be strictly followed.
The introduction of ILT and other diseases onto your farm and into your flock should be the goal of all producers. It is not difficult to do if you follow some common sense guidelines. Don’t move any birds on or off your farm during an ILT outbreak; and don’t visit other poultry farms, fairs, auctions, or exhibitions during an ILT outbreak.
Implement simple biosecurity measures that can be taken to help protect flocks. Buy a pair of rubber boots and wear them only on your own premises, to avoid ‘tracking in’ disease. Use a long-handled brush to scrape off manure, mud or debris from tyres, equipment or boots, and then disinfect. Mix three parts bleach to two parts water, and use it liberally to clean rubber boots and equipment brought onto your farm. If visitors don’t want their vehicle tyres sprayed with disinfectant, ask them to park outside your gate. Don’t be shy about asking visitors to disinfect their footwear. Better yet, provide guests with disposable shoe covers, or footwear worn only on your place.
Figure 1. Swollen, watery eyes
Figure 3. Trachea filled with blood and mucus
Figure 2. Open-mouth breathing