Infectious laryngotracheitis (ILT) is a contagious respiratory disease that is characterised by gasping, neck extension and conjunctivitis (inflammation of the membrane around the eye).
In Queensland, ILT is a notifiable disease under the Stock Act because ILT is similar to the early stages of virulent Newcastle disease, an exotic disease that is as close to Australia as West Irian. If owners, vets, laboratory staff or others suspect this disease, they must report it to Biosecurity Queensland on 13 25 23 or the Emergency Disease Watch Hotline on 1800 675 888.
ILT is caused by a virus that can live for 8 to 10 days in droppings and up to 70 days in carcasses; hence correct disposal is essential. The virus may survive for up to 80 days in tracheal exudate (throat exudate) if not disturbed. This demonstrates the importance of sound clean-up procedures and high-pressure hosing.
ILT affects fowls, pheasants and turkeys. Water fowls (ducks and geese) show no signs but ducks have been known to carry ILT for up to two weeks. Wild birds may act as carriers.
Early signs may include bouts of hard swallowing, ruffled feathers on the back of the head, squinting and the watering of one or both eyes (conjunctivitis).
After the incubation period of 3 to 14 days (though 5 to 12 is most common), increased mucus forms in the trachea, often followed by tracheal haemorrhage. This causes the bird to cough and extend its head in a characteristic manner to breathe. In some cases, only mild respiratory signs are visible but one eye may completely close.
The classic signs are gasping, coughing, and extending the neck forward and upwards with each breath to clear the mucus in the trachea (windpipe). In fact, many birds die from this disease due to suffocation, as the windpipe becomes completely blocked. There has been up to 70 per cent mortality in acute cases.
There is a marked variation in the pathogenicity (potency) of various virus strains. Three major forms are known:
The ILT virus is released from the respiratory tract and followed by rapid airborne transmission among birds in close contact, such as cage or pen mates. The virus enters the bird through the eye, nose or mouth. The coughed-up mucus and blood contains the virus and is another way that the disease quickly spreads.
In the past, most outbreaks have been traced to the movement of poultry, people and equipment. However, if environmental conditions are suitable, windborne spread may also be a factor.
The virus depends on a transporting agent to spread. The virus is not transmitted through the egg, so chickens are not infected at hatching. The virus can be spread via the following means:
Eye-vaccinated birds usually start to show signs on days 3 to 5 and normally finish shedding virus by days 11 or 12.
Wild or field strains cause the birds to shed virus over a longer period than vaccine strains. Again, the period of shedding depends on the incubation time, which is usually longer than for vaccine strains (up to 14 days). The length of the shedding period depends on when the last birds in the building became infected.
This situation can be short-circuited by vaccination; however, a resultant carrier state, where the bird appears normal but may shed virus when stressed, is established in many birds.
The virus can survive for 10 days or more in droppings and up to 70 days in carcasses. The virus lasts longer in winter due to the cool temperature. The virus may survive up to 80 days in tracheal mucus on non-conductive material such as wood. One per cent lysol or three per cent cresol will inactivate the ILT virus in less than a minute.
Sunlight, heat and desiccation (drying) are the three natural enemies of the ILT virus.
|Diagnosis and control|
Acutely affected birds show free blood in the trachea, which is generally associated with a mucus plug that inhibits normal breathing. The symptoms rapidly spread throughout the flock.
Birds with subacute and mild infections may show only slight difficulty in breathing and perhaps a mild watering of one or both eyes. However, the disease can still be easily transmitted from one bird to another. A mild ILT infection may look like any other respiratory or viral infection.
Laboratory diagnosis will always be required to determine whether the ILT virus is present.
ILT may be controlled by:
|Treatment and prevention|
Antibiotics have no effect on the virus. Vaccination and the vaccine's short incubation period is used to halt an outbreak.
The disease is prevented by vaccination. Because ILT is similar to early exotic Newcastle disease, it is maintained as a notifiable disease.
The virus is not transmitted through eggs, so chickens are not infected at hatching.