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ILT is a highly contagious herpes virus infection of chickens, pheasants and peafowls; characterized by severe respiratory distress and bloody tracheal exudates. Other clinical signs include coughing, sneezing, head shaking to dislodge exudates, extension of the neck and open mouth breathing. Inhalation produces a wheezing sound, and severe respiratory distress worsens into asphyxiation from which many die. The incubation period is from 2 to 12 days, and the course of the disease is 7 to 14 days.
The ILT virus survives for long periods in expectorated tracheal clots and in dead birds. The virus remains viable when frozen in organic material, but is easily destroyed by disinfectants or direct sunlight. Virulence varies with the strain. Chickens 14 weeks and older are more susceptible than younger ones, but certain strains of the virus are able to adapt to a younger host, and is sometimes referred to as a hot broiler ILT virus.
Transmission is via direct bird-to-bird contact or contact with infected tissues, dead birds, and contaminated buildings. Because ILT is caused by a herpes virus, exposed birds can harbor the virus in nervous tissue and be clinically normal until a stressful event causes the virus to recrudesce. Recovered chickens remain carriers for as long as 24 months. The probable primary culprit in the spread of the virus is through the purchase of carrier or sick birds. ILT appears to be more of a problem in backyard poultry flocks. Also, the virus may be harbored in specialty poultry, e.g. exhibition birds, hackle strains, and game-fowl.
ILT Summary of the 2008 Season
The disease continues to be a threat to the Alberta poultry industry and has been diagnosed in three backyard flocks to date this year (around 1600 exposed birds). In two cases, the virus appeared to have been spread through birds traded at a livestock auction whereas in the third case, the virus was apparently introduced with purchase of laying birds from a neighbouring flock. In all three cases, the resident susceptible birds in the flock who were from commercial strains of broilers and layers developed the disease shortly after the introduction of infected but clinically healthy birds from backyard poultry flocks. Mortality was in the range of 30 to 40%.
To prevent recovered birds from becoming carriers of the ILT virus, the producers chose to voluntarily depopulate. All three flocks were destroyed and the carcasses were burnt on farm in order to eradicate ILT virus from the farm and to prevent further spread of the disease.
The Important Role of Private Practitioners
During the three ILT outbreaks this season, veterinarians not only recognized the clinical signs, and provided presumptive diagnoses, but they also harvested the targeted organ (trachea) for testing by the Food Safety Division. They reported the suspect flocks to the Office of the Chief Provincial Veterinarian (OCPV), and provided biosecurity recommendations to the producers to contain the threat until confirmation of the diagnosis. The immediate recognition of this disease was crucial (even in the suspect stage) for a rapid response, which alerted producers, enhanced biosecurity measures and reduced the risk of virus spread to other poultry flocks. A team from OCPV visited each site to observe and record clinical signs and mortalities, collect more samples, assess current biosecurity measures and conduct preliminary trace back.
Education of the producer on the virulence of the disease and the potential risk to other poultry was an essential part of this visit. Within four days of the initial report to the OCPV, the affected flocks were destroyed and properly disposed. Detailed trace back investigation to determine the source of the virus was conducted by investigators from Regulatory Services Division of ARD. Follow-up advice included recommendations for clean-up and disinfection of the premises, how to prevent introduction of the disease and other related biosecurity measures.
Private Veterinary Clinics are Essential Partners
Because of their front line role as the eyes and ears across the province, private veterinary clinics provide a significant advantage in the prevention and control of ILT. If ILT is suspected, it must be reported to the Office of the Chief Provincial Veterinarian. For further information, please see: “Infectious Laryngotracheitis (ILT) in Poultry”; Agri-Facts; Agdex 663-36, June 2008.
Narine Singh, Food Safety Division, Edmonton, AB, Dr. Hernan Ortegon and Dr. Gerald Hauer, Office of the Chief Provincial Veterinarian (OCPV), Edmonton, AB |
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