Infectious Laryngotracheitis (ILT) - Respiratory Herpes Virus of Poultry
ILT is an acute herpes viral respiratory tract infection of chickens and pheasants that may result in severe production losses. Losses occur due to excessive mortality, decreased growth rates and decreased egg production. Disease may affect 5 to 80% of an exposed flock, taking 2 to 4 weeks to go through an entire flock. Infected birds usually die but can recover within 7 to 10 days. Mortality can climb as high as 20% in an infected flock.
Signs of infection appear 6 to 12 days after infection and are characterised by mild to severe clinical reactions. Signs include:
* conjunctivitis, watery eyes and swollen orbital sinuses.
* coughing, sneezing, extended neck, laboured, breathing, wheezing and head shaking.
* bloody exudate on the walls of cages or pens from severe cases.
Infection is usually spread by aerosol. The route of infection is through the upper respiratory tract, where the virus replicates in the trachea and the larynx. Other portals of entry include contact of the virus with the eyes and ingestion of the virus. Mechanical transmission can occur via contaminated equipment, clothing, boots, dead stock and litter.
Control focuses on management practices, emphasising strict biosecurity. Due to vaccination potential to cause disease, veterinary supervision is strongly recommended when the decision is made to go this route. Since both natural infection and vaccination have been shown to produce "carrier" birds, it is extremely important that susceptible chicken flocks are not exposed to vaccinated or previously infected chickens. Mixing of birds should only be done when a complete history of the birds is available, and it is absolutely certain that a potential ILT "carrier" is not present. Sanitation procedures, which include disinfection of equipment, boots and clothing and proper disposal of litter and carcasses, are essential components of ILT control.
It should be emphasised that it is always recommended that producers work with their poultry veterinarian for diagnosis and to develop treatment and prevention/vaccination strategies.
Submission of samples to the Animal Health Laboratory should be representative of the problem on the farm or backyard flock. Your history sheet, submitted with the birds, should include: the type of operation, the number of birds at risk, the number of birds affected and the vaccination history. Submit tissues from separate birds in tightly sealed and labelled Whirl-Pak bags for rapid distribution to the designated laboratory sections. For histology, use formalin fixed sections of trachea, larynx and bronchioles. For isolation of ILT virus, trachea and lung are required.
By Scott Gillingham - Veterinary Scientist/OMAFRA
Ministry of Agiculture, Food and Rural Affairs
Dear Sir,
A student Mr. Syedkaleemuhassan raised a question that, could the vaccinated birds act as a carrier or/not, and if do so should we not use the vaccination strategy or can.
With regarding on this I would say that while preparing the vaccine some ingredients such as virus/bacteria that would be the source of antigen, adjuvant to enhance the immunity and to produce a depo at the site of vaccination, etc. are being added. This produced vaccines may be killed/live or attenuated, accordingly they are processed and become marketed for livestock purposes. While processing vaccination the virulent factors that could cause disease and so to produce death is inactivated/killed by any means that defines only the antigenic nature of the organism would be retained by eliminating all other determinants that are responsible to produce disease. In this case, if the vaccine is not prepared upto the level of standard or inactivation or attenuation is not done accurately. the vaccine may carry the disease producting property and so, there is no doubt that vaccinated birds would act as a carrier and it is implied. Moreover, the virus/bacteria should not have any mutating property in itself and this wouldl also can modify the antigenic property and may cause the disease.
Dr. Sathiyabama Kannan
United States
