Spatial and temporal variation in infectious laryngotracheitis viral genome in broiler flock dust post vaccination

Infectious laryngotracheitis (ILT) is an economically important disease of chickens that is endemic in several important poultry production regions of Australia. Outbreaks commonly occur in meat chicken flocks and mass vaccination, usually in water, is used to control the disease and limit its spread during outbreaks. Vaccination with live virus via water and nipple drinkers requires stringent adherence to protocols to ensure success. Evaluation of vaccination success is not performed due to a lack of practical and economic methodologies. ILT vaccine virus has been shown to be detectable in dust following vaccination in experimental studies and offers a potential method of assessing vaccination success. The pattern of vaccinal infectious laryngotracheitis virus (vILTV) detection in commercial poultry dust following vaccination has not been defined in commercial flocks to date and this is the purpose of this study. We report the longitudinal profile of vILTV genome copies (GC) in dust following vaccination of 8 flocks/sheds of commercial meat chickens on four farms. vIL TV GC could be detected in poultry dust after vaccination using quantitative real-time polymerase chain reaction ( qPCR). There was considerable variation between flocks in the pattern observed and this variation was associated with vaccination success measured in individual birds. There was no significant effect of sampling location within sheds on vIL TV GC (P = 0.90). Results suggest that measurement of vIL TV GC in a single pooled sample at days post vaccination 7 or 8 may enable discrimination between vaccination success and failure and provide practical means of monitoring vaccination.