Intervention strategies for laryngotracheitis: impact of extended downtime and enhanced biosecurity auditing.

An outbreak of vaccinal infectious laryngotracheitis (LT) began in 2005 involving 57 ranches of two broiler companies in California. Standard biosecurity, and cleaning and disinfection programs along with vaccination, did not stop the outbreak. Due to the close proximity and number of birds in the same geographic area, the decision was made by both companies to attempt a joint regional and zonal depopulation strategy. The strategy involved extended downtime between flock placements on ranches located within close proximity to one another. This extended downtime on each ranch ranged from 30 to 91 days. An extensive biosecurity audit, with more than 70 items, was implemented. Briefly, this included heating all houses to 37 C for 100 hr, removing the litter, cleaning and disinfecting everything on the ranches, then again heating the houses to 37 C for 100 hr. Used litter was spread on crops away from poultry, or was sent to a litter processor for pasteurization. Extensive surveillance for LT at 28, 35, and 42 days of age was performed on the initial flocks, which had been placed immediately after the extended downtime. Since completion of this plan in early 2008, LT was diagnosed on only two of the previously 57 affected ranches. Those two ranches, and those within close proximity, went through the extended downtime program and biosecurity audit a second time. Currently, both companies are free of LT. This program lends credence to the importance of cooperation between companies to consider all the ranches within close proximity as the population at risk. In the control of LT in broilers, the program also highlights the necessity for extended downtime and enhanced biosecurity auditing of all flocks.