Poultry Diseases - Infectious Laryngotracheitis (ILT)



March 2018Contact: Margaret Sexton (08) 8429 0913Poultry Diseases - Infectious Laryngotracheitis (ILT)Infectious Laryngotracheitis (ILT) is a highly contagious respiratory disease characterised by gasping, neck extension and conjunctivitis.In most states, ILT is a notifiable disease.224663021844000The Causative AgentILT is caused by a Herpes virus. It may retain infectivity for 8 to 10 days in droppings and longer in carcasses, hence correct disposal is essential. It is believed that the virus may survive for up to 80 days in coughed up mucous.Species affectedThe virus can cause disease in fowls, peahen, pheasants and turkeys. Water fowl (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.-38107937500After an incubation period of three to 14 days, there is increased mucus formation in the windpipe (trachea), often followed by tracheal haemorrhage and discharge from the eyes due to conjunctivitis. Meat chicks will show a marked reduction in feed intake and growth rate while layers will suffer a drop in egg production.The classical signs are gasping, coughing and neck extension with each breath in an effort to clear the mucus and debris build up in the windpipe. Many birds die from suffocation, the windpipe becoming completely blocked. In severe cases, there has been up to 70% mortality.Post-mortem findings include blood stained mucus or clots of blood and dead tracheal lining that has fallen off and found in the upper respiratory tract. Death is normally by suffocation.TransmissionThe ILT virus is released from the respiratory tract and there is rapid airborne transmission among birds in close contact. The virus enters the bird through the eye, the nose or the mouth. The coughed-up mucus and blood contains virus and is another means of quick spread of the disease. Most outbreaks have been traced to the movement of poultry, people and equipment. If environmental conditions are suitable, windborne spread must also be considered.The virus depends on a transporting agent to get around. It is not transmitted through the egg so chickens are not infected at the time of hatching.Introduction of infected birds; a major means of spread of the disease is by the introduction of affected birds, carrier birds or birds incubating the disease at the time of introduction. Carriers of ILT can shed virus at times of stress thus infecting susceptible in-contact birds. In show bird flocks, it is common to get outbreaks after birds have been transported to, and returned home from, a show.People and contaminated equipment; these can also carry infection into any flock. Contaminated crates and catching crews have been known to spread infection. People in contact with infected birds and on the same day contacting susceptible flocks may transfer the disease if suitable precautions are not taken.Airborne spread; ILT airborne spread depends on the prevailing conditions. There is rapid airborne transmission among birds in close contact. The virus often requires mechanical transfer to cover even short distances such as from one building to another but there is anecdotal evidence for movement between farms on strong prevailing winds. Diseased birds being transported may infect birds in sheds close to the road. Under conditions of cloud cover, humidity or showers and gusting winds, it would appear that the ILT virus can easily cover 500 metres and possibly much further. Small feathers and dander are ideal transporting agents.Litter and manure; ILT virus may survive in the birds' environment for some time, transmission occurring when susceptible birds are placed in a contaminated and unsanitised environment.Infectious PeriodIndividual birds are infectious from about the end of the incubation period and up to another two weeks. Even the vaccine strains can be shed for this period after inoculation and may cause disease in susceptible birds, although usually milder than field strains. The viral shedding period depends on when the last birds in the building became infected.Many birds develop a carrier state with the virus hiding away in the facial nerves until the bird immunity wanes. If some stress occurs, many of these birds can shed infectious virus and some may even show disease, again usually a milder form but posing a risk to susceptible birds in close contact.DiagnosisThe clinical signs of bloody tracheal discharges or diphtheritic membranes on the epiglottis, conjunctivitis and the high pitched wheezy cough are usually diagnostic but the milder forms need laboratory testing to make sure.Differential DiagnosisVitamin A DeficiencyFowl PoxTrichomoniasisNewcastle DiseaseAvian InfluenzaInfectious Coryza (Avibacterium paragallinarum)Infectious BronchitisTreatmentThere is no treatment but vaccinating early in an outbreak can slow the spread and reduce the clinical effects in the rest of the flock.PreventionVaccinating birds, first with a mild vaccine strain then about four to six weeks later with a more virulent vaccine strain produces an immunity that lasts at least a year. Moulted flocks should be done again at the end of the moult.There should also be proper biosecurity on commercial farms, i.e. strict quarantine with control of people and materials entering the farm and particularly the poultry sheds.Author: Dr Kim Critchley, Poultry Health, PIRSAFOR FURTHER INFORMATION: Contact your local veterinary practitioner.IF YOU HAVE SIGNS OF UNUSUAL OR SERIOUS ANIMAL DISEASE*, phone Biosecurity SA Animal Health at Glenside on 82077900, contact your local PIRSA Animal Health officer, call your local veterinary practitionerOR RING THE DISEASE WATCH HOTLINE: 1800 675 888.*Signs such as mass mortality events, sudden onset of multiple ill birds, rapid spread of a problem or a noticeably unusual illness in birds. ................
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