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Infectious laryngotracheitis (ILT), a highly infectious, acute viral disease, is proving a significant challenge for producers right across the broiler belt.

Work over the last few years has shown that the use of both modified-live virus (MLV) and recombinant vaccines is a viable part of strategies to tackle the disease. But peaks in ILT prevalence have been known to lead to vaccine shortages due to the intermittent nature of the condition, with manufacturers facing issues in planning production to meet demand.

With continued wild-type challenges in the field, those in the industry are faced with a choice of two vaccination options with proven results — with different priorities affecting the final decision made.

Providing immunity when an outbreak rages

Although ILT has not proven as much of a problem for Wayne Farms as for others recently, it was a “top-five disease” for the company only a few years ago, explained Mark Burleson, DVM, its director of veterinary services.

With production of a large number of older birds in an area where the disease has historically been prevalent, chicken-embryo-origin (CEO) MLV vaccines have generally — but not exclusively — been employed.

“We’ve used it primarily to provide immunity to otherwise at-risk, naïve birds where an ILT outbreak is starting or ongoing. In the past, when we’ve hesitated to use CEO vaccine and relied on recombinant vaccines alone, those birds would typically break with ILT and become a source of further viral spread,” he said.

“I use the analogy that using CEO is the best way to put out a fire that’s already raging. Other vaccination methods alone, in my experience, have a harder time doing that.”

Their vaccination approach has typically resulted in immunity developed 2 weeks post-vaccination, as assessed by virus-neutralizing antibodies, and measurable bird performance is rarely affected.

“We are typically vaccinating chickens that will be processed at 8 to 9 weeks, so the bird performance comment may not be shared by those processing younger chickens,” he stressed.

Live vaccine comes with manageable risks

Burleson notes that MLV vaccines do pose a risk of further viral spread, making proper handling especially important.

“To maximize immunity and reduce impacts on bird performance, one has to specifically focus on dosage, route and uniformity of vaccine administration,” he said.

Wayne Farms has successfully used both types of vaccine as part of its overall strategy, with CEO vaccine given to at-risk farms and a recombinant to the rest.

“If CEO vaccine is treated as the live ILT virus in terms of administration, vaccination zones, biosecurity, etc., it can co-exist with recombinant vaccines,” he added.

“Ultimately, ILT vaccine selection boils down to risk. When risk drops to a manageable level, I think it’s responsible to transition away from CEO vaccine. The longer the live virus stays in the environment, the greater risk there is to infect a naïve flock of chickens.

“It’s important to understand that during the transition off a CEO vaccine, any farm that received the live vaccine must be treated as an ‘infected’ farm until the vaccinated flock is processed. This includes the litter the flock was raised on as well.”